Full Program, Posters, and Meeting Planner
Schedule:
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SUNDAY
6:00 PM — Opening Reception (Harp’s Corner at the Harpa Center)
MONDAY
8:30 AM — New Discoveries [Chair: Fred Rasio]
George Ricker (MIT) – Review of TESS’s First Year Survey and Future Plans
Successfully launched in April 2018, NASA’s Transiting Exoplanet Survey Satellite (TESS) is well on its way to discovering thousands of exoplanets in orbit around the brightest stars in the sky. During its initial two-year survey mission, TESS will monitor more than 200,000 bright stars in the solar neighborhood at a two minute cadence for drops in brightness caused by planetary transits. This first-ever spaceborne all-sky transit survey is identifying planets ranging in size from Earth-sized to gas giants, orbiting a wide variety of host stars, from cool M dwarfs to hot O/B giants.TESS stars are typically 30–100 times brighter than those surveyed by the Kepler satellite; thus, TESS planets are proving far easier to characterize with follow-up observations than those from prior missions. Such TESS followup observations are enabling measurements of the masses, sizes, densities, orbits, and atmospheres of a large cohort of small planets, including a sample of habitable zone rocky worlds.An additional data product from the TESS mission is its full frame images (FFIs), which are collected at a cadence of 30 minutes. These FFIs provide precise photometric information for every object within the 2300 square degree instantaneous field of view of the TESS cameras. In total, nearly 100 million objects brighter than magnitude I = +16 will be precisely photometered during the two-year prime mission.The initial TESS all-sky survey is well underway, covering 13 observation sectors in the Southern Ecliptic Hemisphere during Year 1, and 13 observation sectors in the Northern Ecliptic Hemisphere during Year 2. A concurrent, year-long deep survey by TESS of regions surrounding the North and South Ecliptic Poles will provide prime exoplanet targets for characterization with the James Webb Space Telescope (JWST), as well as other large ground-based and space- based telescopes coming online in the next two decades. The status of the TESS mission as it completes its first year of survey operations in July 2019 will be reviewed. The opportunities enabled by TESS’s unique lunar-resonant orbit for an extended mission lasting more than a decade will also be presented.
Eric Nielsen (Stanford) – The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics from 10-100 AU
The Gemini Planet Imager Exoplanet Survey (GPIES) has observed 521 young, nearby stars, making it one of the largest, deepest direct imaging surveys for giant planets ever conducted. With detections of six planets and four brown dwarfs, including the new discoveries of 51 Eridani b and HR 2562 B, GPIES also has a significantly higher planet detection rate than any published imaging survey. Our analysis of the uniform sample of the first 300 stars reveals new properties of giant planets (>2 MJup) from 3-100 AU. We find at >3 sigma confidence that these planets are more common around high-mass stars (> 1.5 solar masses) than lower-mass stars. We also present evidence that giant planets and brown dwarfs obey different mass functions and semi-major axis distributions. Our direct imaging data imply that the giant planet occurrence rate declines with semi-major axis beyond 10 AU, a trend opposite to that found by radial velocity surveys inside of 10 AU; taken together, the giant planet occurrence rate appears to peak at 3-10 AU. All of these trends point to wide-separation giant planets forming by core/pebble accretion, and brown dwarfs forming by gravitational instability. If our power-law model that fits giant planets around high-mass stars is also applicable to solar-type stars, and these power-laws remain valid down to the mass of Jupiter and inward to 5 AU, then the occurrence rate for giant planets more massive than Jupiter within 100 AU could be less than 40%. Looking beyond these results, we present our early analysis of the full GPIES sample, whether these trends persist over all 521 observed stars, and implications for future observations from Gemini-North with an upgraded GPI.
David Charbonneau (Harvard) – Three Red Suns in the Sky of the Nearest Exoplanet Transiting an M Dwarf
The only terrestrial exoplanets whose atmospheres will be spectroscopically accessible in the near future will be those that orbit nearby mid-to-late M dwarfs. We present the discovery from TESS data of LTT-1445Ab, a terrestrial planet transiting an M dwarf only 6.9 parsecs away, making it the closest known transiting planet with a small-star primary. Remarkably, the host stellar system is composed of three mid-to-late M dwarfs in a hierarchical configuration, which are blended in a single TESS pixel. We use follow-up observations from MEarth and the centroid offset from the TESS data to determine that the planet transits the primary star in the system. The planet has a radius 1.35 times that of Earth, an orbital period of 5.36 days, and an equilibrium temperature of 428 K, and the mass should be readily measurable with radial velocity observations in the coming months. The system is particularly favorable for ground-based observations to advance the study of the atmospheres of terrestrial exoplanets: Such observations are typically performed using multi-object spectrographs on large telescopes, but previous studies have been limited by the need to use blue field stars to calibrate telluric variations, which have provided a poor color match to the red target stars. Here, the companion stars provides an ideal telluric calibrator, namely one of nearly equal brightness and similar spectral type located only 7 arcseconds from the target. This work is supported by grants from the National Science Foundation and the John Templeton Foundation.
Anne-Marie Lagrange (Grenoble) – Evidence for an Additional Planet in the Beta Pic System
With its well resolved debris disk of dust, its evaporating exocomets, and an imaged giant planet orbiting at about 9 au, the young (~23 Myr) β Pictoris system is a unique proxy for detailed studies of planet formation and early evolution processes as well as planet-disk interactions. We have studied 10 years of ESO/HARPS high resolution spectroscopic data on the star. After removing the δ Scuti pulsations, a ~1200 days periodic signal is observed. Within our current knowledge, we can only attribute this signal to a second massive planet orbiting at ~2.7 au from the star (Lagrange et al, 2019, Nat. Astron., under minor revisions). To our knowledge, this is the first system hosting a planet detected in imaging and one detected with indirect technics. I will present the evidence for this additional planet, and analyse the impact of this result on previous results, including previous analysis of GAIA astrometric data, the system dynamical stability, the exocomets activity.
Laura Kreidberg (Harvard) – Absence of a Thick Atmosphere on a Terrestrial Exoplanet
I will present a thermal phase curve measurement for a terrestrial exoplanet recently detected by the TESS mission. The planet is in a short period orbit around a nearby M-dwarf star. The phase curve is the first such measurement for a planet smaller than 1.6 Earth radii, the size below which the existence of an atmosphere is unknown a priori. The amplitude of the phase variation puts strong constraints on the planet’s atmospheric properties, which I will discuss.
Calen Henderson (Caltech/IPAC-NExScI) – Recent Microlensing Results: Individual Systems and Demographic Frontiers
Over the past several years, the field of gravitational microlensing has made myriad advancements with regard to characterizing individual planetary systems, exploring relatively unknown demographic regimes, and developing tools and resources for community use. Here I will highlight a handful of results that lead to precise planet masses for microlensing planets, including (A) measuring the microlens parallax effect (e.g., Street+ 2016); (B) using high-resolution photometry to constrain the flux of the lens (e.g., Bhattacharya+ 2018); (C) complementing microlensing photometry with astrometric and spectroscopic data (Han+ 2019); and (D) deriving the Einstein radius through interferometry (Dong+ 2019). I will also discuss recent demographic studies, including (i) constraining the frequency of free-floating planets (e.g., Mróz+ 2017, 2018; Poleski+ 2014); (ii) determining the Galactic distribution of exoplanets via a multi-year Spitzer program (cf. Yee+ 2015); and (iii) understanding and contextualizing the planet-star mass-ratio distribution (Suzuki+ 2016, 2018; Pascucci+ 2018). Finally, I will conclude by describing the public tools and data provided, in particular by the WFIRST Microlensing Science Investigation Team, to allow for the larger exoplanet community to get involved with immediate science and also help prepare for the WFIRST microlensing survey.
10 AM — Coffee Break
10:30 AM — Direct Imaging [Chair: Anne-Marie Lagrange]
Michael Meyer (U Michigan) – Frequency of Massive Wide-orbit Planets vs. Stellar Mass: SPHERE SHINES on the ESO VLT
We describe the SpHere INfrared Exoplanet (SHINE) survey, a key part of the SPHERE GTO Program on the ESO VLT, and present new statistical analyses of the frequency of gas giant planet occurrence as a function of host star mass. Constraining the frequency of the most massive planets, as well as the lowest mass brown dwarf companions, at wide orbital separations vs. host star mass, enables us to discern the mean outcomes of planet formation, thus defining what is extreme in the context of planetary architectures. In addition, our data provides a strong test of predictive theories of star and planet formation. This high contrast imaging survey has discovered and characterized dozens of very low mass companions (1-76 MJUPITER), on wide orbits (10-1000 AU) around a range of host star masses (0.3-3 MSUN). Three papers in preparation (Desidera et al.; Langlois et al.; Vigan et al.) describe the survey sample and strategy, data reduction and analysis techniques, and the first statistical results. Our survey, constraining the frequency of gas giants 1-10 MJUPITER, as well as brown dwarf companions, from 10-100 AU, suggests: 1) the frequency of gas giants around FGK (and other) stars peaks between 1-10 AU; 2) the gas giant planet mass function appears to be a universal power-law relative to host star mass, explaining the trend of gas giant detection rate of with star mass; 3) the brown dwarf companion mass function is consistent with extrapolation from a universal stellar companion mass ratio distribution down to the minimum mass for fragmentation; and 4) some, but not all, relevant predictions made by D.N.C. Lin are thankfully inconsistent with these data.
Brendan Bowler (UT Austin) – Population-Level Eccentricity Distributions of Imaged Exoplanets and Brown Dwarf Companions
The dominant formation channel of long-period directly imaged exoplanets and brown dwarf companions has been challenging to unambiguously constrain with observations because of their low occurrence rates, limited composition measurements, and degeneracies among theoretical predictions. Eccentricities offer a robust tool to assess the origin of these populations because they directly trace the dynamical imprint after formation and any subsequent orbital evolution. In this talk I will discuss new results on the underlying eccentricity distributions of directly imaged exoplanets and brown dwarf companions. We have carried out homogeneous orbit fits based on new high-contrast imaging observations together with a compilation of astrometry from the literature to assess the individual and population-level eccentricity distributions of over two dozen long-period giant planets and brown dwarfs between 5-100 AU using hierarchical Bayesian modeling. Each companion traces out a small orbit arc which typically results in a broad constraint on its individual eccentricity, but together as an ensemble these systems provide valuable insight into their collective underlying orbital patterns. The population-level eccentricity distributions for the subset of giant planets (2-15 Mjup) and brown dwarf companions (15-75 Mjup) are significantly different and provide compelling dynamical evidence for distinct formation pathways. As a population, long-period planets preferentially have low eccentricities, suggesting formation within a disk. The brown dwarf subsample is dynamically hotter with a broad peak at high eccentricities, which is qualitatively similar to binary stars. Larger samples and continued astrometric orbit monitoring will help establish whether these eccentricity distributions correlate with other parameters such as stellar host mass, multiplicity, and system age.
Cecilia Lazzoni (INAF – Padova) – Two Giant Exomoons Around Two Low-mass Brown Dwarf Companions Detected with SPHERE
It is still unclear if brown dwarfs companion detected with the direct imaging technique were formed as stars or planets. The analysis of their multiplicity can provide clues on their formation mechanism. In this context, we analyzed the residuals around brown dwarf companions observed with SPHERE during the SHINE/GTO with the technique of negative fake planets to look for features around them. We found an extended source around one of the brown dwarf in the sample that would suggest the presence of a disk and two candidate companions, massive gaseous exomoon-like objects, bound to other two brown dwarfs. These latter would represent the first triple systems ever discovered with two substellar companions, one in the planetary regime and the second just above the deuterium burning limit.
Kate Follette (Amherst) – Accreting Protoplanets from the 2013-2018 MagAO Giant Accreting Protoplanet Survey (GAPlanetS)
The Magellan Giant Accreting Protoplanet Survey (GAPlanetS) is the most sensitive high-contrast imaging survey for actively forming planets to date. Conducted over 5 years (2013-2018) and with over 75 hours of open shutter time on 15 of the brightest transitional disks, the GAPlanetS survey pioneered the H-alpha differential imaging technique. With three accreting companions (two protoplanets and one low mass stellar companion) successfully detected within the relatively small sample, the GAPlanetS survey demonstrates the bright future of protoplanet direct imaging. I will present aggregate statistics and results of the full survey, including reprocessings under a unified and robust framework of the three previously-published GAPlanetS detections (HD 142527B, PDS 70b, LkCa 15b), as well as important limits on the presence of accreting planets in gapped disk systems such as TW Hya. I will discuss lessons learned about hardware and software techniques for starlight suppression in these morphologically complex transitional disk systems, where disk material and planets coexist and can be confused. I will end by discussing the next generation of ground and space based protoplanet imaging technologies and instruments, including MagAOX and WFIRST.
Valentin Christiaens (Monash) – PDS 70 b: Evidence for a Circumplanetary Disc Around the First Directly Imaged Protoplanet
The observed properties of the major moons of Jupiter — and of other gas giants — have suggested that they formed within a circumplanetary disc. This prediction has been supported by theoretical calculations and numerical simulations of increasing complexity over the past few decades. Despite intensive search, circumplanetary discs had until now eluded detection. In this talk, I will present the first observational evidence for a circumplanetary disc, around recently imaged protoplanet PDS 70 b. Our detection is based on a new near-IR spectrum acquired with VLT/SINFONI. We tested several hypotheses (atmospheric emission alone, variable extinction, combination of atmospheric and circumplanetary disc emission) to explain the spectrum and show that models considering atmospheric emission alone consistently underpredict the longward portion of the spectrum. Our best fit is obtained with a combined atmospheric and circumplanetary disc model, with emission from the circumplanetary disc accounting for the apparent excess IR emission.
Matt Holman (Harvard-Smithsonian CfA) – A Pan-STARRS and TESS Search for Distant Planets
Several lines of evidence, both theoretical and observational, indicate that additional planets in the outer solar system remain to be discovered. We recently developed a novel technique to search for solar system bodies (Holman et al. 2018). This method is particularly well-suited to very slow-moving objects, even those for which the motion within a day might be to small to detect. We present the results of our use of this method to search for distant planets and minor planets in existing Pan-STARRS and TESS data.Perhaps even more important than the search itself is a detailed, quantitative analysis of the survey’s detection limits and biases. This information is essential for the rigorous interpretation of these survey results. Such simulators have been developed for CFEPS/OSSOS, NEOWISE, and other surveys, leading to detailed results on the small body populations throughout the solar system. We have developed a high-fidelity survey simulator for Pan-STARRS and have extended it to TESS. This simulator takes positions, magnitudes, and rates of motion calculated from a solar system model (Grav et al 2011) at the times and locations of individual exposures. It then inserts synthetic detections into the resulting exposure source catalogs, accounting for the details of the camera, photometric zero point, and other essential details. The source catalogs, including synthetic detections, are then run through our full search pipeline. This approach allows a clear, quantitative statement about the prevalence of distant planets, as seen by Pan- STARRS and TESS.
Sasha Hinkley (Exeter) – Studying the Interior Structure of an Extremely Eccentric Hot Jupiter via Deep VLT Imaging
I will describe how our group at Exeter has used the VLT-SPHERE instrument to place constraints on the internal structure of HD 20782b, a Hot Jupiter with the most extreme eccentricity known to date (e~0.96). In the dynamically-driven migration scenario (e.g. Kozai-Lidov cycles combined with tidal dissipation), a Jupiter mass planet is dynamically excited to a high eccentricity by a third body, and its orbit subsequently shrinks and circularizes through tidal dissipation. Our deep observations of the HD 20782 system rule out any additional (third) companions with masses in the range 20-60 Jupiter masses at orbital separations ~10-60 AU that might be responsible for exciting the extreme eccentricity of the inner planet. Our lack of detections of any additional companions in the system indicates that the eccentricity of the planet was gained early on and has persisted until the present. The apparent failure of the tidal dissipation mechanism in this system means that we can place strong constraints on the tidal quality factor “Q” of HD 20782b. Specifically, our models of planetary tidal evolution suggest a remarkably high value for the planet’s tidal Q factor of 107 – 108: two to three orders of magnitude higher than that measured for other extrasolar planets, as well as members of our own solar system. Our result suggests a possible structural difference between HD 20782b and other giant planets inside and outside our solar system. If time allows, I will discuss how our approved 52-hour JWST Early Release Science Program will pave the way for future observations of additional systems with extremely eccentric planets starting in 2021. JWST will illuminate the interior structures of many more eccentric Jovian mass planets going forward, or possibly even image the extremely eccentric planets themselves.
Lunch Break
2:00 PM — Radial Velocities [Chair: Didier Queloz]
Xavier Dumusque (Geneva) – HARPS and HARPS-N Solar Telescopes: The Key to Extremely Precise Radial-velocity Measurements
Detecting and measuring the masses of planets in the presence of stellar signals is the main challenge we are facing when using the radial-velocity (RV) technique. Even in the TESS era where planetary periods are known, obtaining a precise mass, which is critical to constrain further planetary composition and thus planetary formation, is challenging.
Critical to a better understanding of RV variations induced by stellar signals and finding correction techniques is RV data with a sampling sufficient to probe timescales ranging from minutes to years. To address this challenge, our team built two solar telescopes that feed sunlight into HARPS-N and HARPS, which allows us to obtain Sun-as-a-star RVs at a sub-m/s precision. In this talk, I will present the data that obtained during the last 4 years with HARPS-N and nearly a year with HARPS. I will show how the two datasets match at a level of 40 cm/s within a day, which allows to characterize p-modes, granulation signal, and stellar activity on the rotation timescale of the Sun, which we know are the main limitations to precise RVs. With these data, we start to improve our understanding of how stellar signals affect RVs: – CCF-line shape variability correlates with RVs with a significant time-delay that prevents using shape variations directly as a proxy for stellar activity. – RV correlates strongly with total magnetic field strength, which makes sense as magnetic regions are at the origin of most stellar signal. – With the extreme SNR that we reach on the Sun, we see that when analyzing the RV of individual spectral lines, some are much more sensitive to stellar activity than others, due to differing formation height in the stellar photosphere.All these new insights into stellar signals give us the key to develop the techniques capable of mitigating their impact down to a level that will allow the detection and characterization of Earth-twins using the RV technique.
Stefan Dreizler (U Goettingen) – Rocky Planets from the CARMENES Survey
CARMENES, operated since 2016, is a high-resolution visible-near-IR spectrograph dedicated to search for such low- mass planets around low-mass stars and already doubled the number of known planets with host stars below 0.2 M Sun. Not surprisingly, also this stellar parameter range has its surprises in terms of planetary system architectures. We will give an overview of exoplanet detections (published and unpublished) from the CARMENES survey and then concentrate on the low-mass planets, including the very recent detection of two Earth-mass planets around Teegarden’s star highlighting the capability of CARMENES. The planetary system is special since Teegarden’s star is only one out of three planet host stars with an effective temperature below 3000K. Its two planets are within the optimistic and conservative habitable zone, respectively. Notably, the Earth, as well as other Solar System planets are currently or in near future in the transit visibility zone see from Teegarden’s star.
Mario Damasso (INAF – Torino) – A Low-mass Planet Candidate Orbiting Proxima Centauri at a Distance of 1.5 AU
By analyzing ~17 years of radial velocity data of Proxima Cen collected with the UVES and HARPS spectrographs, we detected a signal of period P~5 years that could be explained by the presence of a second planet, Proxima c, with minimum mass m sin i~6. Earth masses. Together with the low-mass temperate planet Proxima b, this candidate planet would make Proxima the closest multi-planet system to the Sun. We will present the properties of the new RV signal and investigate the likelihood that it is related to a magnetic activity cycle of the star. We will discuss how the existence of Proxima c can be confirmed, and its true mass determined with high accuracy, by combining Gaia astrometry and radial velocities. Proxima c would be a prime target for follow-up and characterization measurements, especially with next generation direct imaging instrumentation due to the large maximum angular separation of ∼1 arcsecond from the parent star. Since the orbit would be beyond the original location of the snowline, Proxima c would challenge the models of the formation of super-Earths. Presently, this study is under review by Science Advances.
Caroline Piaulet (Montreal) – New Insights into the Keystone WASP-107 System
With the radius of Jupiter, the near-Neptune-mass planet WASP-107 presents a major challenge to planet formation theories. Meanwhile, the system’s brightness and planet’s low surface gravity makes it a keystone target for spectroscopic characterization, especially in the poorly-probed low-temperature ($T_{eq}<800$K) regime. In this talk, we will present the main results of an extensive follow-up program of WASP-107b using over 2 years of Keck/HIRES radial velocities as well as $>$60 hours of Spitzer observations. The radial velocity data reveal an even lower planetary mass than previously thought. The inferred 1.8 Neptune mass indicates an extraordinarily high H/He mass fraction of 80\% accreted by a core of only $7\pm3$ Earth masses. The resulting lower surface gravity means that all the transmission spectroscopy for this planet has to be reinterpreted. With Spitzer, we furthermore detect the thermal emission of this 720K exoplanet at 3.6$\mu$m, indicating substantial eccentricity ($e = 0.129^{+0.028}_{-0.011}$) and making it the best target for eclipse observations with JWST in this temperature regime. A puzzling brightness temperature contrast between the 3.6 and 4.5$\mu$m bandpasses presents direct evidence for disequilibrium chemistry, and makes WASP-107b a keystone target to unveil the underlying mechanisms of quenching and atmospheric dynamics. We show that the non-zero eccentricity of WASP- 107b could result from the presence a second planet in the WASP-107 system on a highly eccentric ($e = 0.56^{+0.11}_{-0.14}$) and wide ($\sim$2000d) orbit, which we also detect in the radial velocity data. Overall, the joint constraints from the secondary eclipse and RV observations shed unprecedented light on the rich dynamics history of this peculiar planetary system offering an intriguing possibility for the origin of close-in exo-Neptunes like WASP-107b.
Sarah Blunt (Caltech) – Radial Velocity Discovery of an Eccentric Jovian World Orbiting at 18 AU
We announce the discovery of the longest-period planet with a well-constrained orbit discovered with radial velocities (RVs). HR 5183 b, with P=75$\pm$30 yr, e=0.84$\pm$0.04, and M$\sin{i}$=3.23$\pm$0.14 M$_J$, was detected independently in more than two decades of data from Keck/HIRES and McDonald/Tull. The highly eccentric orbit takes the planet from within the orbit of Jupiter to beyond the orbit of Neptune over one period. Because of this high eccentricity, orbital information density is strongly peaked around periastron, which occurred in January 2018. By observing this periastron passage event with high cadence, we were able to place tight constraints on the orbital parameters without witnessing an entire orbital period.In terms of semimajor axis and mass, HR 5183 b is most similar to a typical directly imaged planet, but its advanced age, extreme eccentricity, and solar-type primary star differentiate it from this population. This discovery probes a previously unexplored population of exoplanets, highlighting the value of long-baseline RV surveys and raising interesting questions about the long-term evolution of planetary systems with massive planets.
René Doyon (Montreal) – First Results from the SPIRou Legacy Survey
SPIRou is the infrared high-resolution echelle spectropolarimeter currently in operation on the Canada- France-Hawaii telescope, an instrument specifically designed and optimized to achieve precision radial velocity at infrared wavelengths. SPIRou features a unique polarimetric capability, high resolving power (70 000) and a very broad simultaneous wavelength coverage between 0.98 to 2.5 microns. SPIRou has two main science goals: detect small planets around nearby low-mass stars and explore the impact of magnetic field of star/planet formation. SPIRou has been allocated a 300-night Legacy Survey over a period of 4 years that was initiated in February with the following main science objectives: 1) search for small planets around low-mass stars, 2) provide mass measurements for new transiting planets from TESS and other transit surveys and 3) observe a large sample of pre-main sequence stars to detect and characterize hot Jupiters at early evolutionary stages and to investigate planet formation and planet/disc interactions. Thanks to its wide wavelength range, SPIRou is also a very powerful capability for atmospheric characterization of transiting exoplanets. This talk will present an overview of the instrument and its on-sky performance along with a highlight of the first science results obtained so far as part of the Legacy Survey.
3:30 PM — Coffee Break
4:00 PM — Transits [Chair: David Charbonneau]
Adina Feinstein (U Chicago) – Expectations vs. Reality: The Exoplanet Yield in the TESS Full-Frame Images
During its two year prime mission, the Transiting Exoplanet Survey Satellite (TESS) will perform a time-series photometric survey for 80% of the sky, observing 26 24×96 degree sectors of the sky each for 27 days. The primary objective of TESS is to find transiting planet candidates around 200,000 pre-selected stars for which fixed aperture photometry is recovered every two minutes. However, TESS is also recording and delivering Full-Frame Images (FFIs) of each detector at a thirty minute cadence. Using the eleanor pipeline, which creates light curves for all stars in the FFIs, we have begun a uniform transit search for targets in multiple sectors. In this talk, I will highlight several of the current findings within the FFI data. I will discuss our reduction and vetting processes, specifically highlighting the most common false positives found within the data, how we identify them, and how we remove them from the final data set. As TESS has already proven a successful mission and has been awarded an extended mission, we will continue to search the FFIs for new planet candidates to further our understanding of the exoplanet population, especially those of longer periods, and its implications for finding new planets in this data set.
Peter Plavchan (George Mason U) – Newly Formed Planets within the Debris Disk of a Pre-main-sequence Star
We report a two-planet system orbiting a young star with a debris disk, one inner planet discovered using data from NASA’s TESS mission and a second planet with multi-wavelength radial velocities. The two newly identified planets in this system can be used to investigate disk-planet interactions and inform the planet formation and migration process.
Andrew Vanderburg (UT Austin) – New Discoveries and Progress Towards Planet Occurrence Rates in Kepler, K2, and TESS
Deep learning, a cutting edge machine learning technique, is leading to remarkable advancements in fields ranging from biomedical imaging to linguistics. Our team is leveraging this technology to discover new exoplanets and characterize their populations. We have built and tested neural networks to classify and vet transiting planet candidates from Kepler, K2, and TESS and identified new exoplanets from large sets of unclassified signals. Our discoveries include two super-Earths from the K2 mission, a new planet in a five-planet resonant chain around Kepler 80 and an eighth planet around Kepler 90, making this the most extreme solar system known in number of planets. I will give an overview of deep learning, describe our newly discovered planets, and discuss the path forward to using these deep learning classification tools to measure planet occurrence rates in Kepler, K2, and TESS.
Diana Dragomir (U New Mexico) – The HD 21749 System: A Temperate Sub-Neptune, an Earth-sized planet, and Who Knows What Else
Our understanding of multi-planet systems has been dominated by Kepler discoveries, our understanding of multis is nowhere near complete. With TESS we have the opportunity to fill in missing pieces, like precise masses and orbital eccentricities of planets in multis, and to search for non-transiting planets with radial velocity measurements. I will present the recent discovery of HD 21749 (jointly enabled by TESS and existing ground-based observations), a multi-planet system with an intriguing architecture. It includes an unusually dense (7 g/cm^3) sub-Neptune in a mildly eccentric 35.6-day orbit, and a 0.9 Earth radius planet with a period of 7.8 days, around a K dwarf star located 16 pc away from the Sun. A similar architecture (in terms of periods, and non-zero eccentricity of the outer planet) has surfaced in four other systems known to host small/low-mass planets. The host stars of HIP 57274, HIP 7924 and HIP 69830 are also K dwarfs, but these systems are not known to transit so only lower limits are available on their masses, and no radius measurement. The periods of the two known low-mass planets in the K2-18 system (9 and 33 days) are very similar to those of HD 21749 b and c, but while K2-18b has a radius and a mass measurement, planet c does not transit and only has a lower mass limit. Moreover, the host star is a M dwarf, and thus planet formation probably differed between those two systems. With prospects for a mass measurement of planet c in the near future, HD 21749 is poised to become the best characterized system with this emerging architecture. We have continued monitoring this system with Magellan-PFS radial velocities, leading to improved constraints on the orbital eccentricity of planet b, and on the presence and properties of additional planets in the system. I will also show results from a dynamical analysis of the system, which provide an independent constraint on the mass of planet c and on islands of stability where other planets could orbit. Lastly, I will explore a few exciting follow-up avenues within reach, including prospects for atmospheric characterization and orbital obliquity measurements.
Antonija Oklopcic (Harvard) – Detecting Magnetic Fields in Exoplanets with Spectropolarimetry in the Helium Line at 1083 nm
Most planets in the solar system have or previously had a global magnetic field, yet not much is known about magnetic fields in exoplanets. Information about the presence of a magnetic field and its strength could give us valuable insights into the interior structure and thermal evolution of an exoplanet. Furthermore, a global magnetic field on an exoplanet could have important consequences for the extent, composition, and evolution of its atmosphere, by controlling atmospheric escape and its interaction with the stellar wind. In this talk, I will present a new method for detecting magnetic fields in the atmospheres of close-in exoplanets, based on spectropolarimetric transit observations at the wavelength of the helium line at 1083 nm. Strong absorption signatures (transit depths on the order of a few percent) in the 1083 nm line have recently been observed for several close-in exoplanets. Most of the work so far has been focused on measuring and interpreting the effects of extended or escaping planetary atmospheres on the radiation intensity at 1083 nm; however, a wealth of information can be stored in radiation polarization as well. I will describe how linear and circular polarization signals in the helium 1083 nm line arise in the presence of an external magnetic field due to atomic level polarization induced by anisotropic stellar radiation, and the combined action of the Zeeman and Hanle effects. This phenomenon has been well established in solar physics as a means to probe the magnetic field properties of the solar chromosphere and corona, and I will demonstrate how the diagnostic power of this method can be extended to the field of exoplanets. Assuming exoplanetary magnetic fields with strengths comparable to the magnetic fields observed in the solar system planets, polarization signals in the helium 1083 nm line should be detectable with modern high-resolution spectropolarimeters operating at these wavelengths.
Ji Wang (Ohio State) – The Most Metal-Poor Planets Around the Oldest Stars in Milky Way
The Gaia-TESS synergy opens up a new window to peer through planet formation in the galactic context. We can finally answer the following question: when and how did the first planet form? By selecting ~27,000 halo stars, the oldest stellar population in the Milky Way, via their galactic kinematics provided by Gaia, we conduct the most conprehensive study on chemical abundance of halo stars using SDSS/APOGEE spectra, and the search for the most metal-poor planets using TESS data. The study leads to discoveries of a few planet candidates through TESS sector 9 and the characterization of their stellar enviroment. We will report the exciting discoveries, the follow- up observations for planet confirmation and validation, and the implications on planet formation in extremely metal- poor enviroment in the infant universe.
James Jenkins (U Chile) – TESS Discovery of the First Ultra Hot Neptune, LTT9779b
In this talk I will discuss the discovery of a super Neptune orbiting the bright and metal-rich star, LTT9779. The planet was first detected as a candidate in data from Sector 2 of the Transiting Exoplanet Survey Satellite (TESS), and subsequent ground-based photometric and spectroscopic follow-up confirmed its reality and constrained its mass. With an orbital period of only 19 hours, this world is the first Neptune-like ultra short period planet, and with an equilibrium temperature greater than 2000 K, it can be classed as the first Ultra Hot Neptune. I will discuss the detection and confirmation of this new planet, possible origins, and highlight the unique opportunities it presents for atmospheric characterisation and further follow-up. Finally, I will briefly discuss additional small planet candidates from TESS that we are actively following up in Chile, both to confirm them as bonafide planets and also to constrain their radii, masses, and bulk densities.
TUESDAY
8:30 AM — Dynamical Evolution [Chair: Eric Ford]
Dong Lai (Cornell) – Low-Eccentricity Formation of Ultra-Short Period Planets in Multi-Planet Systems
Recent studies suggest that ultra-short period planets (USPs), Earth-sized planets with subday periods, constitute a statistically distinct sub sample of Kepler planets: USPs have smaller radii (1-4 Earth radii) and larger mutual inclinations with neighboring planets than nominal Kepler planets, and their period distribution is steeper than longer-period planets. We study a “low-eccentricity” migration scenario for the formation of USPs, in which a low-mass planet with initial period of a few days maintains a small but finite eccentricity due to secular forcings from exterior companion planets, and experiences orbital decay due to tidal dissipation. USP formation in this scenario requires that the initial multi-planet system have modest eccentricities (~0.1) or angular momentum deficit. During the orbital decay of the inner-most planet, the system can encounter
several apsidal and nodal precession resonances that significantly enhance eccentricity excitation and increase the mutual inclination between the inner planets. We develop an approximate method based on eccentricity and inclination eigenmodes to efficiently evolve a large number of multi-planet systems over Gyr timescales in the presence of rapid (as short as 100 years) secular planet-planet interactions and
other short-range forces. Through a population synthesis calculation, we demonstrate that the “low-e migration” mechanism can naturally produce USPs from the large population of Kepler multis under a variety of conditions, with little fine tuning of parameters. This mechanism favors smaller inner planets with more massive and eccentric companion planets, and the resulting USPs have properties that are consistent with observations.
Rosemary Mardling (Monash) – Relaxation of Resonant Two-planet Systems and their TTVs
Many two-planet systems reside near or inside first-order resonances, while many multi-planet systems form resonant chains. These are normally the product of planet-disk interactions during the time of formation, with eccentricity damping and migration resulting in a relaxed system with fewer degrees of freedom than for an arbitrary two-planet system. Are most multi-planet systems in this state? Even if they reside `far’ from resonance? A simple formulation describing two-planet systems will be presented which is valid inside, across and outside resonance. We will show that all such systems are governed by a single two-parameter ordinary integro-differential equation, and that all system information (variation of eccentricities, orbital frequencies, resonance angles, apsidal orientations, transit timing variations or TTVs) can be derived from its solution. An expression for the TTVs can be easily inverted to solve for the planet masses (and other system parameters) when both planets transit; if no valid inversion is possible (given sufficient signal to noise for the TTVs), it is possible to infer the existence of additional non-transiting planets, the signature of which will be imprinted on the signal.
Smadar Naoz (UCLA) – Signatures of Hidden Friends to Multiplanet Systems
Multiplanet systems seem to be abundant in our Galaxy. These systems typically feature tightly packed multiple super-Earths or sub-Neptunes with periods less than a few hundred days. Moreover, these systems seemed to be dynamically calm, with nearly co-planar and circular orbital configurations. In contrast, a significant fraction of single, close in, planets found by Kepler, have larger orbital eccentricities. Is the single planet population a result of the instability episode of the multiplanet population? If so, what triggered the instability? A possible cause for instability is gravitational interactions with a distant companion. Radial velocity surveys found a population of giant planets and companions at far distances from their host star (e.g., Knutson et al. 2014; Bryan et al. 2016). Moreover, distant (few AUs) planetary and stellar companions were identified to orbit some specific tightly packed multiplanet systems (e.g., Uehara et al. 2016, Bryan et al. 2019, Mills et al. 2019). These companions co-exist with their inner multiplanet system and do not trigger dynamical instability. Thus, we ask, what are the allowable orbital configurations that friends for stable multiplanet systems? I this talk I will present an analytical criterion that specifies the possible orbital configuration of a far away companion to a multiplanet system. I will also provide a set of predictions for the possible distant companion’s orbital architecture of existing systems, such as Kepler-56, Kepler-448, Kepler-88, Kepler-109, and Kepler-36. Finally, I will show that a distant companion can affect the planets’ obliquity with respect to their orbital angular momentum. In turn, this has a unique observable signature on the planets’ flux incident at the top of the atmosphere as a function of orbital phase.
Kassandra Anderson (Cornell) – In-Situ Excitation of Warm Jupiter Eccentricities: Implications for Dynamical Histories & Migration
Warm Jupiters (giant planets with orbital periods 10-300 days) are a major topic in exoplanetary dynamics, given their possible links to hot Jupiters, and unresolved puzzles regarding their dynamical histories and migration. Many planets show hints of a violent past, with substantial eccentricities. High-eccentricity tidal migration is a natural mechanism for producing eccentric warm Jupiters, but struggles to reproduce other characteristics of the warm Jupiter population. This talk discusses alternative dynamical mechanisms for raising eccentricities, starting from a low-eccentricity state consistent with either a disk migration origin or in-situ formation. First I discuss eccentricity growth due to secular perturbations from an external giant planet companion, through an apsidal precession resonance (for low-inclination systems), or Lidov-Kozai cycles (for highly-inclined systems). Taking the sample of warm Jupiters with characterized giant planet companions, I evaluate the prospects for secular eccentricity excitation, and find that high mutual inclinations (at least 40-50 degrees) are typically needed to produce observed eccentricities. The results of this work place constraints on possibly unseen external companions to eccentric warm Jupiters. Next I discuss the possibility of producing eccentric warm Jupiters due to in-situ formation of three giant planets, followed by planet-planet scattering. Scattering at sub-AU distances from the host star results in a combination of planet collisions and ejections, producing comparable numbers of one-planet and two-planet systems. Two-planet systems arise exclusively through planet-planet collisions, and tend to have low eccentricities/inclinations and compact configurations. One-planet systems arise through a combination of ejections and collisions, resulting in much higher eccentricities. The observed eccentricity distribution of solitary warm Jupiters is consistent with roughly half of systems having undergone in-situ scattering, and the remaining having experienced a quiescent history.
Renata Frelikh (UC Santa Cruz) – Signatures of a Planet – Planet Impacts Phase in Exoplanetary Systems Hosting Giant Planets
Giant planets are often found on substantially non-circular, close-in orbits. An important clue for their dynamical histories has not yet been explained in theories for the origins of their eccentricities: most planets with high eccentricities (e>0.6) tend to also be planets of higher mass (m>1 MJ). This is surprising: the orbits of the lower-mass planets in a system are typically the most easily excited. Furthermore, these eccentric planets are preferentially found around stars that are metal-rich. We propose that these eccentricities arise in a phase of giant impacts, during which the planets scatter each other and collide, with corresponding mass growth as they merge. We numerically integrate an ensemble of systems with varying total planet mass, allowing for collisional growth, to show that (1) the high- eccentricity giants observed today may have formed preferentially in systems of higher initial total planet mass, and (2) the upper bound on the observed giant planet eccentricity distribution is consistent with planet-planet scattering.
Jacques Laskar (Obs Paris) – AMD-stability of Planetary Systems
Due to the increasing large number of discovered planetary systems, it becomes important to set up some framework for a rapid understanding of the dynamics of the discovered systems, without the need of computer intensive numerical simulations. This has been the goal of our recent work on AMD-stability. In a planetary system, the AMD (Angular Momentum Deficit) is the difference between the planar circular angular momentum and the total angular momentum. This quantity is conserved between collisions in the average system, and decreases during collisions. This leads to the concept of AMD-stability. A planetary system is AMD-stable if the AMD in the system is not sufficient to allow collisions. The advantage of this notion is that it becomes possible to verify very quickly whether a newly discovered planetary system is stable or potentially unstable, without any numerical integration of the equations of motion. These principles have been applied to the 131 multiple planetary systems of the exoplanet.eu database whose orbital elements are sufficiently well determined (Laskar and Petit, 2017a). AMD-stability, based on the secular evolution, addresses to long time stability, in absence of mean motion resonances. On the other hand, criterions for short term stability have been established on the basis of Hill radius (Marchal & Bozis 1982; Gladman 1993; Pu & Wu 2015) or on the overlap of mean motion resonances ( Wisdom 1980; Duncan et al. 1989; Mustill & Wyatt 2012; Deck et al. 2013). Both long and short time scales can be combined owing some modification of the AMD-stability criterion (Petit, Laskar & Boué, 2017b). Finally, Hill stability can be expressed in a very effective and simple way in the AMD framework ( Petit, Laskar, Boué, 2018).
10 AM — Coffee Break
10:30 AM — Ultrashort Periods and Planet-Star Interactions [Chair: Evgenya Shkolnik]
Ray Jayawardhana (Cornell) – Remote Sensing of Extreme Worlds: High-Resolution Spectroscopy of Exoplanet Atmospheres
High-resolution spectroscopy, combined with the Doppler cross-correlation technique, is emerging as a powerful and robust probe of exoplanet atmospheres. Here we will report on our wide-ranging observational program targeting Jovian-mass worlds, sub-Saturns and super-Earths using a suite of frontline instruments in the optical as well as the near-infrared. In particular, we will present new findings and on-going work related to two of the hottest gas giants and a very hot terrestrial planet. With a dayside at ~4000K, KELT-9b is a so-called ultra-hot Jupiter with a temperature akin to those of dwarf stars. Transmission spectra reveal a host of metal lines in its atmosphere. With new Calar Alto/CARMENES observations, we not only confirm strong Halpha in its extended exosphere, but also report robust detections of the resolved CaII triplet for the first time (paper in prep.). We have also observed two transits and portions of six phase curves of WASP-33b (~3000K), with Keck/HIRES and CFHT/ESPaDOnS to obtain transmission and emission spectra at high spectral resolution, to detect molecular signatures of TiO and water vapor (paper in prep.) Finally, we report a sensitive new search for water vapor and TiO in the atmosphere of the nearby very hot super-Earth 55 Cancri e (~2700 K) using a combination of data from Gemini/GRACES, Subaru/HDS and CFHT/ESPaDOnS (paper submitted). Our findings suggest that unless the signal is suppressed significantly by clouds/haze, this planet may well be bone-dry. Moreover, we have recently obtained high-resolution near-infrared spectra of 55 Cnc e from CARMENES at Calar Alto as well as the brand-new SPIRou instrument on the CFHT, and expect to present first results at ESS IV.
Joseph Callingham (ASTRON) – Stellar Systems at Low Radio Frequencies: The Discovery of Radio Exoplanets
For more than thirty years, radio astronomers have searched for auroral emission from exoplanets. With LOFAR we have recently detected strong, highly circularly polarised low-frequency (144 MHz) radio emission associated with a M-dwarf – the expected signpost of such radiation. The star itself is quiescent, with a 130-day rotation period and low X-ray luminosity. In this talk, I will detail how the radio properties of the detection imply that such emission is generated by the presence of an exoplanet in a short period orbit around the star, and our follow-up radial-velocity (RV) observations with Harps-N to confirm the exoplanet’s presence. Our study highlights the powerful new and developing synergy between low-frequency radio astronomy and RV observations, with radio emission providing a strong prior on the presence of a short-period planet. I will conclude the talk detailing how the radio detection of an star-exoplanet interaction provides unique information for exoplanet climate and habitability studies, and the extension of our survey to other stellar systems.
Josh Winn (Princeton) – Observations of Tidal Orbital Decay of Hot Jupiters
Soon after the discovery of 51 Peg b, Rasio et al. (1996) and Lin et al. (1996) realized that tidal interactions between hot Jupiters and their host stars may lead to significant orbital evolution. In particular, the orbits of almost all of the known hot Jupiters should be shrinking due to tidal orbital decay. The timescale for tidal decay is unknown and depends on the mechanism by which tidal oscillations of the star are dissipated as heat, a longstanding source of uncertainty in stellar astrophysics. The best opportunity to detect orbital decay directly is through long-term transit timing. I will present the results of search for orbital decay among the dozen most favorable hot Jupiters, some of which have now been observed for more than a decade. WASP-12 shows a clear decrease in the transit period which seems likely to be caused by either tidal orbital decay or apsidal precession. I will present two new seasons of transit observations, and four new Spitzer observations of eclipses, that help to distinguish between these possibilities. In addition to WASP-12, two other candidates for orbital decay have been identified, but the evidence is not compelling and further observations are needed. I will also discuss the prospects for detecting orbital decay using data from the Transiting Exoplanet Survey Satellite.
Taylor Bell (McGill) – Mass Loss from the Exoplanet WASP-12b Inferred from Spitzer Phase Curves
As an exoplanet orbits its star, the thermal radiation coming from the planet varies roughly sinusoidally, with a peak occurring when the hottest hemisphere of the planet faces the observer. A Spitzer Space Telescope phase curve of the ultra-hot Jupiter WASP-12b from 2010 showed an unexplained anomaly in the data; unlike every other planet observed to date, the infrared signal from WASP-12b showed two maxima per planetary orbit, rather than one (Cowan et al. 2012). Stranger still, this was only seen at a wavelength of 4.5 μm, while the phase curve at 3.6 μm showed only one maximum. At the time, the authors dismissed this finding as being the result of detector systematics. We present new work which robustly confirms the findings of Cowan et al. (2012) through the analysis of new Spitzer phase curves taken in 2013, as well as the reanalysis of their original data. We obtain consistent results at both epochs using three independent analyses. We rule out the possibility of detector systematics, nor can tidal distortion of the planet or star explain these variations. We then show that these observations require the planet to be undergoing mass loss, likely in the form of a gas stream flowing directly from the planet to the star. While mass loss has been predicted for WASP-12b, our inferred flow geometry is unanticipated. We also find strong evidence for atmospheric variability, with the offset in the phase curve maximum at 3.6 μm changing by more than 6σ between the two sets of observations.Our findings provide an independent confirmation of past claims of mass loss from near-ultraviolet transit observations. We also show that our observations provide new constraints on the composition, flow geometry, and temperature of the gas stripped from the planet. For example, the wavelength dependence of the gas emission may suggest that the gas is rich in CO. Finally, many of the past findings regarding the atmosphere of WASP-12b, one of the best-studied exoplanets, will need to be reconsidered in light of the contamination from the escaping gas.
Sarah Millholland (Yale) – Tidally-Induced Radius Inflation of Sub-Neptunes
Recent work suggests that many short-period super-Earth and sub-Neptune planets may have significant spin axis tilts (“obliquities”). When planets are locked in high-obliquity states, the tidal dissipation rate increases by several orders of magnitude. This intensified heat deposition within the planets’ interiors should generate significant structural consequences, including atmospheric inflation leading to larger transit radii. Using up-to-date radius estimates from Gaia Data Release 2 and the California-Kepler Survey, we show evidence for larger average radii of planets wide of first-order mean-motion resonances, a population of planets with theorized frequent occurrence of high obliquities. We investigate whether this radius trend could be a signature of obliquity tides. Using an adaptation of the Modules for Experiments in Stellar Astrophysics (MESA) stellar evolution toolkit, we model the evolution of the H/He envelopes of sub-Neptune-mass planets in response to additional internal heat from obliquity tides. The degree of radius inflation predicted by the models is indeed consistent with the observations, suggesting that these planets have likely been inflated. We present several case studies that are particularly strong candidates for having undergone this process. Broadly speaking, we find that tidal dissipation can affect a sub-Neptune’s radius to first order, yet it has not been included in previous interior structure models. This must be accounted for if the valley in the super-Earth/sub-Neptune radius distribution is to be fully understood.
Ben Montet (U Chicago) – The Life Expectancy of Hot Jupiters
Short period giant planets are theorized to spiral into their host stars on relatively short timescales, with the exact rate of inspiral dependent on the strength of tidal forces on main sequence stars. Thus, by measuring the occurrence rate of hot Jupiters as a function of time, one can effectively measure the strength of stellar tidal dissipation. For this, one must measure the ages of stars. I will discuss two avenues through which we can accomplish this for planet hosts. The first is an analysis of the NGC 6791 cluster, an old (8 Gyr), metal-rich ([Fe/H] ~ +0.3) cluster observed throughout the Kepler mission. While this cluster is too crowded for planet searches through traditional pipelines, we (have) developed a PSF modeling scheme to search for and find transiting planets in and toward this cluster. I will present the results from this search and the implications for the destruction of hot Jupiters in time.We can also understand the ages of planet hosts when they are associated with other, well-characterizable stars. Gaia is now providing us with data on widely separated, co-moving systems across the sky, including in the Kepler and K2 fields. With two stars, we can use isochronal or gyrochronological information on the non-planet hosting star in the system to understand the system age, without worrying about potential tidal spin-up from the existing hot Jupiter. I will present how this method is helping us understand the ages of field stars, the rate of tidal spin-up by hot Jupiters on their host stars, and the long-term evolution of these planetary systems. I will also examine how data from Kepler and K2 can be useful for understanding the prevalence of lithium-rich red giants across the sky, potentially answering a longstanding question in stellar physics.
Carole Haswell (Open U) – Key Planets for Exogeology in the 2020s: Discoveries from the Dispersed Matter Planet Project
HST revealed a complete lack of chromospheric emission from extreme hot Jupiter (hJ) host star WASP-12. We since found ~40% of hJ hosts have anomalously low chromospheric emission in Ca II H&K. We attribute this to absorption in diffuse circumstellar gas, originiating from the highly irradiated planets. Archival spectra of thousands of bright, nearby stars revealed a few main sequence field stars with similar deficits in the Ca II H&K line cores. These stars were not known planet hosts; we hypothesized they harboured, close-in, mass-losing, low mass, small planets. The Dispersed Matter Planet Project (DMPP) targets them, making high precision, high cadence RV measurements to find ~Earth-mass planets in short period (<~6 d) orbits. We have found planets wherever we have more than 60 RV measurements. We will present results from our first three planetary system discoveries, statistical assessment of our underlying hypotheses, and sketch the implications of our findings.
Lunch Break
2:00 PM — Stellar Spins and Obliquities [Chair: Josh Winn]
Simon Albrecht (Aarhus U) – New Developments on the Obliqueness of Exoplanet Systems
The angle between the rotation axis of a star and its orbital angular momentum – its obliquity – conveys information about the formation and evolution of the star and its planetary system. Here I report on new trends and results we have recently obtained and their possible interpretations. Our results give new indications about which mechanisms are responsible for generating large obliquities in some systems, and whether tidal alignment is an important factor in shaping obliquity distributions. (1) We have found that high eccentricities and high obliquities are linked, suggesting that close-in giant planets can be separated into dynamically cool and dynamically hot populations, in line with other recent results. (2) Observations of protopanetary disks as well as some models suggest that protoplanetary disks need not be well-alighed with the stellar equator. However, out of the ten obliquity measurements in multi transiting systems (tracing the disk plane) only one has coplanar planets on an oblique orbit. And even in this exceptional system, Kepler-56, the large tilt may be caused by a fourth body, not primordial misalignment. We have also tentatively identified a multi-transiting system in which the planets appear to travel on retrograde orbits. Additional transit observations are scheduled for June and should clarify the situation. (3) Tidal alignment has been invoked to explain the observed dependence of the obliquity distribution on the host star’s effective temperature, the planet-star mass ratio, and the orbital separation. However, theoretical and observational counterarguments exist. We report on two new trends that suggest tides are indeed important: (i) Stars with retrograde planets have a lower projected stellar rotation speed than prograde stars. (ii) Effective temperature is a better predictor of high obliquity than stellar mass. We show that the current sample of 140 systems with reliable obliquity measurements is generally consistent with a picture of tidal alignment.
Marshall Johnson (Ohio State) – The Spin-Orbit Misalignment Distributions of Hot Jupiters
Many hot Jupiters have orbits that are highly misaligned with respect to the stellar rotation; most misaligned planets orbit stars above the Kraft break, which is generally though to be the result of less efficient tidal damping in hotter stars. Many mechanisms have been proposed to generate misaligned orbits, but previous observational constraints have been unable to definitively distinguish among these mechanisms. We present initial results from an extensive program to address this problem using statistical analyses of the spin-orbit misalignments of hot Jupiters around A and early F stars, and correlations with other parameters of the systems.We demonstrate that there is not a sharp break in the spin-orbit misalignment distribution at the Kraft break as typically assumed, but rather a more gradual transition; a significant population of well-aligned planets exists up to at least Teff~6600 K, and early F stars’ planets require a two-population model. Less massive and longer-period planets tend to have more misaligned orbits, consistent with expectations from tidal damping, suggesting that the tidal damping of obliquities around these stars may be stronger than previously assumed. There is no correlation between metallicity and misalignment, contrary to expectations from planet-planet scattering. We present results from new Keck NIRC2 non-redundant aperture masking interferometry observations, coupled with archival high-resolution imaging and Gaia DR2 astrometry, to perform a comprehensive survey for stellar companions to these stars from a few to tens of thousands of AU. Such companions could drive migration and misalignments via the Kozai-Lidov mechanism. We tentatively find that hot Jupiters with stellar companions have more misaligned orbits than those that do not, contrary to previous results.We are also leveraging Gaia DR2 parallaxes and TESS light curves to measure these stars’ densities and radii and thus infer their ages and the orbital eccentricities. We demonstrate that we are typically able to measure their ages to a precision of 500 Myr, much better than is typically possible for field stars. We present initial results from this work.
Cristobal Petrovich (CITA) – Tilting Short-period Planetary Systems in Photo-evaporating Disks
The current sample of nearly a dozen Neptune-mass planets with stellar obliquity measurements reveals a surprising population that move on nearly polar orbits (4 planets with obliquities of ~90 degrees, e.g., GJ 436b, HAT-P-11b). The absence of stellar companions and the likely presence of nearby planetary companions in these systems makes the current proposals to drive large obliquities in hot Jupiter systems (e.g., primordial disk misalignments or high-eccentricity migration) inapplicable to these sub-Jovian planets.In this talk, I will show that large stellar obliquities in short-period planetary systems are naturally excited by a distant (>1 AU) Jovian companion embedded in a photo-evaporating disk. This excitation is the result of secular resonances and often leads to polar planetary systems, even if the primordial tilts are small (~5 degrees), revealing that: (i) the disk dispersal phase plays a major role at shaping the architecture of planetary orbits; (ii) large obliquities might be intimately linked to the observed misalignments between inner and outer disks in many transitional disks.Beyond the small sample of sub-Jovian planets with obliquity measurements, we show that our proposed mechanism fits well within the observed trends of obliquities with stellar metallicities and orbital separations found in the Kepler sample. Finally, we provide with predictions from this mechanism that can be immediately tested by ongoing follow-up campaigns with TESS, as well as future Gaia’s astrometric measurements.
Shweta Dalal (IAP) – Nearly Polar Orbit of the Sub-Neptune HD3167 c: Constraints on a Multi-planet System Dynamical History
We present the obliquity measurement, that is, the angle between the normal angle of the orbital plane and the stellar spin axis, of the sub-Neptune planet HD3167 c, which transits a bright nearby K0 star. We study the orbital architecture of this multi-planet system to understand its dynamical history. We also place constraints on the obliquity of planet d based on the geometry of the planetary system and the dynamical study of the system. New observations obtained with HARPS-N at the Telescopio Nazionale Galileo (TNG) were employed for our analysis. The sky-projected obliquity was measured using three different methods: the Rossiter-McLaughlin anomaly, Doppler tomography, and reloaded Rossiter-McLaughlin techniques. We performed the stability analysis of the system and investigated the dynamical interactions between the planets and the star. HD3167 c is found to be nearly polar with sky-projected obliquity, λ = -97 +/- 23 degrees. This misalignment of the orbit of planet c with the spin axis of the host star is detected with 97% confidence. The analysis of the dynamics of this system yields coplanar orbits of planets c and d. It also shows that it is unlikely that the currently observed system can generate this high obliquity for planets c and d by itself. However, the polar orbits of planets c and d could be explained by the presence of an outer companion in the system. Follow-up observations of the system are required to confirm such a long-period companion.
Gudmundur Stefansson (Penn State) – Precision R-M Observations of M-Dwarf Planets in the Near-Infrared with the Habitable-zone Planet Finder
Significant progress has been made in recent years in measuring the sky-projected obliquity distribution of FGK planet hosting systems via precise Rossiter-McLaughlin (RM) effect observations. However, currently only one M-dwarf system, GJ 436 has a published obliquity constraint via the RM effect—which interestingly is observed to be misaligned. With only one published measurement, key questions remain about the dynamical histories of M-dwarf planets. The advent of stabilized extremely precise RV spectrographs in the near-infrared (NIR) is opening the doors to answering these questions, capitalizing on the large RM-effect amplitudes—large compared to their Doppler RV amplitude—produced by transiting exoplanets orbiting around rapidly-rotating M-dwarfs. In this talk, we will discuss recent precision RM effect observations of fully-convective M-dwarfs with the Habitable-zone Planet Finder (HPF), a stabilized NIR spectrograph recently commissioned on the 10m Hobby-Eberly Telescope at McDonald Observatory. We will discuss recent RM effect observations of the fully-convective M-dwarfs K2-25b, and TRAPPIST- 1b, early results of which favor aligned and misaligned orbits, respectively, yielding important insights into the formation history and evolution of these systems.
Marta Bryan (UC Berkeley) – First Constraints on the 3D Angular Momentum Architecture of a Planetary System
Studying 3D architectures of planetary systems presents a unique window into their formation histories. A full description of a system’s geometric orientation requires measuring the stellar spin, planetary spin, and orbital angular momentum vectors. In the past, studies have focused on just one or two of these vectors, namely the orbital plane and the stellar spin axis. For instance, measurements of projected spin-orbit alignment have found a number of hot Jupiter systems that are misaligned, raising the possibility that the misalignments resulted from higheccentricity migration and dynamical interactions between planets. In addition, while discoveries of multi-planet compact coplanar systems indicate smooth disk migration, a handful of these systems exhibit spin-orbit misalignment, suggesting the disk itself was tilted relative to the stellar spin axis. While these partial views of 3D architectures provide an important perspective on planet formation, we can learn even more about system formation histories by characterizing all three angular momentum vectors. Here we present our study characterizing the three angular momentum vectors of the directly imaged single-planet system 2M0122-2439. In this study we measure for the first time projected spins for both star and planet from our NIR high-resolution Keck/NIRSPEC spectra. We combine these with our new stellar photometric rotation period measurement from TESS data and with a previously published planetary rotation period to obtain spin axis inclinations for both objects. We fit multiple astrometry epochs, including two unpublished epochs, to constrain the companion’s orbital inclination. With these pieces needed to measure the three angular momentum vectors, we provide first measurements of the planetary obliquity, stellar obliquity, and relative inclinations between star/planet spin axes, allowing us to place new constraints on this system’s formation history.
3:30 PM — Coffee Break
4:00 PM — Transiting Multi-planet Systems [Chair: Eve Lee]
Trevor David (JPL/Flatiron) – A Family of Newborn Planets Transiting a Young Solar Analog at 20-30 Myr
Compact, multi-planet systems are one of the defining discoveries of the Kepler mission. These planetary systems are ubiquitous in the galaxy yet much about their nature remains a mystery, including whether they formed in situ and what their architectures were when the protoplanetary disk dispersed. Theoretical models suggest that close-in Kepler planets had radii that were roughly 2 to 10 times larger at the time of disk dispersal. With the recent discoveries of exoplanets transiting young stars (<100 Myr), it is now possible to put these models to the test and study close-in planets at a stage when contraction, cooling, and initial atmospheric loss are still underway. To date, only a few exoplanets have been discovered transiting pre-main sequence stars, all of which are currently single-planet systems. I will discuss the recent detection of four transiting planets larger than 5 Earth radii orbiting within ~0.5 AU of a young solar analog aged between 20-30 Myr. The inner planets are larger than Neptune and expected to be actively losing envelope mass through photo-evaporation. The outer planets are both Jupiter-sized and, with separations >0.15 AU, they are expected to be largely shielded from the effects of photo-evaporation. Consequently, the outer planets may be particularly valuable benchmarks, with properties that may more closely reflect the initial conditions of Kepler planets. In a single system, we thus have the opportunity to study proto-Kepler planets across a range of insolation fluxes shortly after the accretion of envelopes and at a time when stellar X-ray emission is near its peak.
Sophie Anderson (MIT) – Higher Compact Multiple Occurrence Around Metal-Poor M-Dwarfs
The planet-metallicity correlation provides a potential link between exoplanet systems as we observe them today and the effects of bulk composition on the planet formation process. Many observers have noted a tendency for Jovian planets to form around stars with higher metallicities. However, there is no consensus on a trend for smaller planets. In this talk I will discuss my recent work investigating the planet-metallicity correlation for rocky planets in single and multi-planet systems around Kepler M-dwarf stars. M-dwarfs are too dim to easily make direct elemental abundance measurements using spectroscopy, so we instead used a combination of parallaxes and photometry to find relative metallicities. We used color-magnitude diagrams to show that compact multiple systems prefer metal-poor M-dwarfs, with 73% of compact multiple systems, compared to 55% of single-planet systems, in orbit around a star more metal poor than the average star in the MK vs. GBP – GRP plane. This trend is broadly consistent with other choices of color and magnitude. Our conclusion is that metallicity plays a role in the architecture of rocky planet systems. Compact multiples either form more readily, or are more likely to survive on Gyr timescales, around metal-poor stars.
Dan Fabrycky (U Chicago) – Unlocking the Interpretation of Transiting Multiplanet Systems using High Impact Parameters
Multiplanet systems in which all the planets transit offer clean individual solutions and precise parameter constraints. In this talk, we discuss new ideas and results regarding planetary systems in which some of the members transit with high impact parameter: they enable even better solutions. Moreover, computing multiplanet statistics with impact parameters results in a clear global view of the population and can infer the existence or absence of non-transiting planets. We discuss one individual system in detail: K2-146. In campaign 5 of K2, one planet was known to transit with large transit timing variations (TTVs). In campaigns 16 and 18 we found its perturber to transit also. The two planets form a 3:2 resonance, and the fast precession of the nodes and periastra caused the outer planet’s impact parameter to decrease from 0.99 to 0.89 in the ~3 years spanned by K2 observations, tripling its observed transit depth. Interpreting the transit shape variations along with TTVs allows us to measure the most precise masses (Mp/MEarth = 5.77±0.18 and 7.50±0.23) for any super-Earth or sub-Neptune (Rp/REarth = 2.04±0.06 and 2.19±0.07, respectively). We further infer that these values support photoevaporation models. Zooming out to the population of transiting planetary systems of high multiplicity, we define statistics for mass partitioning (based on radii), spacing complexity (based on periods), and system flatness (based on impact parameters through durations and stellar densities). For the first time, we find the three to be correlated: if a multiplanet system has similar-sized planets that are laid out regularly in period, then it tends to be extremely flat with mutual inclinations <1 deg. We can turn this argument around and infer more rigorously than before that some systems have non-transiting planets — we identify eight systems of 3 planets with conspicuous gaps, where a 4th planet would complete an evenly-spaced set. Far from a blind application of Titius-Bode’s rule, our inference of additional planets derives from system layouts actually observed in the population.
Matthias He (Penn State) – The Intrinsic Distribution of Planetary Systems: Modeling the Impact of Clustering on Planetary Architectures
The Kepler Mission discovered thousands of exoplanet candidates and hundreds of multi-transiting systems, enabling detailed population studies. We present a forward model for generating populations of exoplanetary systems, modeling the Kepler detection pipeline, comparing simulated planetary systems to those observed by Kepler, and performing statistical inference on planetary system architectures, and not just the distribution of individual planets. We show that models assuming independent planet sizes and orbital periods do not adequately reproduce the observed population and can lead to inaccurate inferences about the intrinsic distributions of multiplicities, period ratios, and mutual inclinations. In contrast, our model allowing for the clustering of planet sizes and periods within each system provides a significantly improved description of the Kepler multi-planet systems, especially in modeling the observed multiplicity and period ratio distributions. Our results are consistent with previous studies finding that the observed multiplicity distribution implies two populations of planetary systems, a majority coming from a low mutual inclination (~1°) population with low eccentricities (~0.01) and a second population of systems with high mutual inclinations (or isolated planets) making up ~40% of all systems. However, we find that a large fraction of stars do not harbor any planets (with Rp>0.5R_Earth and 10d<P<300d). Those that do tend to have many. Our model makes predictions for the distribution of additional non-transiting planets that can inform observing strategies for the follow-up of TESS discoveries and can be tested by the findings of upcoming radial velocity campaigns. We provide large simulated catalogs drawn from our models for testing whether apparent trends in the Kepler catalog could be due to observational biases or are evidence of patterns in the true distribution of planetary systems’ physical properties. We provide a public code for simulating both intrinsic and Kepler-observed catalogs of planetary systems enabling comparisons between planet formation models and observations.
Emily Sandford (Columbia) – Linguistic Modeling of Kepler’s Exoplanets
Planets belonging to the same system are related: formed from the same protoplanetary disk around the same star, and in general, size-ordered, with correlated radii and dynamically organized spacing. As a consequence, the individual planets in a system inform upon each other, and upon their yet-unobserved siblings.Here, we apply the techniques of natural language processing to the problems of (i) classifying planets into maximally informative categories, analogous to parts of speech; and (ii) predicting the next unobserved planet orbiting a star. In the case of text interpretation, we expect a word’s context to inform upon the word itself; for example, the incomplete sentence “The plane landed in ____ yesterday” contains enough information to limit the set of sensible missing words to a relative handful.We treat planetary systems as “sentences” made up of planet “words,” ordered from the star outward. By our analogy, we expect the properties of a planet’s host star and neighboring planets to inform us of the likely properties of the planet itself, and we apply the technique of maximizing mutual information (MMI) to model the relationships between these properties.
Joseph Rodriguez (Harvard-Smithsonian CfA) – Compact Multi-Planet Systems With Planets That are “Way Out of Line”
The Kepler Mission led to the discovery of hundreds of multi-planet systems. Remarkably, these systems tend to have relatively flat architectures (less than a few degrees), much smaller than the misalignments seen in our own Solar system. Recently, however, using observations from the K2 mission, we have discovered a compact six-planet system of sub-Neptunes orbiting a nearby (78 pc) K-star, K2-266. Interestingly, this system contains an ultra-short-period (USP) super Earth that is significantly misaligned (>12 degrees) to the other five planets. More recently, we discovered a system of up to five planets around an early K-star TOI 125 using data from the TESS mission. . Similar to K2-266, TOI-125 has a USP planet candidate, that if confirmed, would be misaligned to the rest of the system by ~17 degrees. To date, these systems are the most exoplanet discovered in one system by K2 and TESS, respectively. As a result of their close proximity to their host stars, the USPs in each system actually transit along our line-of-sight. One explanation for the misalignments is that an additional unseen companion resides in each system. In this scenario, the strength of its dynamical coupling could vary between each of the inner planets, potentially resulting in a difference in the evolution of each planet’s inclination, causing the observed misalignment. We will present the discovery and characterization of each systems, and provide a range of parameters for the unseen companion that could explain the misalignment seen in the K2-266 system. J.E.R. is supported by the Harvard Future Faculty Leaders Postdoctoral fellowship.
7:00 PM — Conference Dinner at Perlan
WEDNESDAY
8:30 AM — Planet Formation [Chair: Doug Lin]
Catherine Olkin (SwRI) – Results from the New Horizons Encounter with 2014 MU69 and What They Tell us about Planetary Formation
On January 1, 2019, NASA’s New Horizons mission flew past the cold classical Kuiper Belt Object, 2014 MU69 [1]. This was the furthest encounter of a solar system object and our first close-up look at a cold classical Kuiper Belt Object (CCKBO). As a CCKBO with a circular, low-inclination orbit, 2014 MU69 likely formed at the same heliocentric distance from the protoplanetary disk about 4.5 billion years ago.From the encounter, we learned that this object is a bilobed object composed of two ellipsoidal components. The two lobes are distinct and show no sign of significant disruption at the margin between them indicating that they formed from a low-velocity merger of the two components. The larger component is lenticular in shape with dimension of ~22 x 20 x 7 km while the smaller component is less flattened (~14 x 10 x 10 km). The two lobes have their long axis aligned which would be consistent with the two ellipsoidal parent bodies being tidally locked before their merger. From the color and compositional data collected on the spacecraft, we find no significant differences in average color and no obvious compositional differences between the two lobes. The low-velocity merger and homogeneity of the lobes are consistent with objects forming in pebble cloud gravitational collapse models. In order for the two objects to merge, the system would have needed to lose angular momentum. Preferred mechanisms for this are either (1) interacting with other small bodies in the vicinity and/or (2) gas drag from the protoplanetary disk. Acknowledgements: We thank the New Horizons mission for supporting this work.
Mickey Rosenthal (UC Santa Cruz) – Why Super-Earths are of a Similar Size: Observational Signatures of a Limiting Pebble Accretion Mass Scale
We propose a novel mass scale at which growth by pebble accretion ceases, which has far reaching ramifications for both modeling and observation of planetary systems. By noting that, at scales of order the nascent planet’s atmosphere, the flow of nebular gas is altered by the presence of the planet, we demonstrate that particles that require impact parameters for accretion smaller than this atmospheric scale are inhibited from accreting. Not only does this process determine the smallest particle sizes that be captured via pebble accretion, but at terrestrial and super-Earth masses this “smallest” particle size is often larger than the maximal sizes present in the disk, naturally shutting off pebble accretion. This mass scale, which we term the “flow isolation mass,” is particularly salient due to the rapid growth timescales via pebble accretion for planets of terrestrial and super-Earth masses. Taken at face value, these rapid rates would predict that few planets end their growth in this mass regime; instead planets either “stall” before this scale, or continue their growth and become gas giants. Flow isolation resolves this problem, allowing close-in planets to naturally finish their growth at super-Earth mass scales. We demonstrate that flow isolation can explain several observed features of the transiting planet population. In particular, recent work indicating that super- Earths in the same system are correlated in size, and that the super-Earth population can be produced by a single characteristic core mass, both point to the existence of a limiting core mass scale. For reasonable fiducial disk parameters, the magnitude of the flow isolation mass and its dependence on stellar mass and semi-major axis agree well with these observations.
Eve Lee (McGill U) – The Boundary between Gas-rich and Gas-poor Planets
Sub-Saturns straddle the boundary between gas-rich Jupiters and gas-poor super-Earths/sub- Neptunes. Their large radii (4–8Rearth) suggest that their gas-to-core mass ratios range ∼0.1–1.0. With their envelopes as massive as their cores, sub-Saturns are just on the verge of runaway gas accretion; they are expected to be significantly less populous than gas giants. Yet, the observed occurrence rates of sub-Saturns and Jupiters are comparable within ∼100 days. We show that in these inner regions of planetary systems, the growth of sub- Saturns/Jupiters is ultimately limited by local and global hydrodynamic flows—runaway accretion terminates and the formation of gas giants is suppressed. Within a finite disk lifetime ∼10 Myrs, massive cores (>10Mearth) can become either gas-poor or gas-rich depending on when they assemble but smaller cores (<10Mearth) can only become gas- poor. This wider range of possible outcomes afforded by more massive cores may explain why metal-rich stars harbor a more diverse set of planets. We also speculate on the origin of the fast rise in the occurrence rate of gas-rich planets towards longer orbital periods.
Jennifer Scora (Toronto) – Forming Rocky Super-Earths with Realistic Collisions
Recent data on rocky super-Earths shows that they have a wider distribution of Fe/Mg ratios, or core to mantle ratios, than the planets in our Solar System. We show that this range is too large to be explained by the Fe/Mg ratios of the stars that host them. Instead, we demonstrate that realistic collisions, which alter the composition of the colliding bodies by preferentially stripping debris from the mantle, can explain much of this spread. Planet formation simulations have only recently begun to treat collisions more realistically in an attempt to replicate the planets in our Solar System. We investigate planet formation more generally by simulating the formation of rocky super-Earths with varying initial conditions using a gravitational N-body code that incorporates realistic collisions. We track the maximum plausible change in composition after each impact. The final planets span a wider range of Fe/Mg ratios than the Solar System planets, but do not completely match the distribution in super-Earth data. The most iron-rich planets are similar in Fe/Mg ratio to Mercury, and the most iron-depleted planets are found at lower masses. This indicates that further work on our understanding of planet formation is required to explain planets at the extremes of this Fe/Mg distribution.
John Biersteker (MIT) – Atmospheric Mass Loss due to Giant Impacts: The Importance of the Thermal Component for Hydrogen – Helium Envelopes
Systems of super-Earths and mini-Neptunes display striking variety in planetary bulk density and composition. Giant impacts are expected to play a role in the formation of many of these worlds. Previous works, focused on the mechanical shock caused by a giant impact, showed that these impacts can eject large fractions of the planetary envelope, offering a partial explanation for the observed compositional diversity. I will describe the thermal consequences of giant impacts, and show that the atmospheric loss caused by these effects can significantly exceed that caused by mechanical shocks for hydrogen-helium (H/He) envelopes. During a giant impact, part of the impact energy is converted into thermal energy, heating the rocky core and envelope. We find that the ensuing thermal expansion of the envelope can lead to a period of sustained, rapid mass loss through a Parker wind, partly or completely eroding the H/He envelope. The degree of atmospheric loss depends on the planet’s orbital distance from its host star and its initial thermal state, and hence age. Close-in planets and younger planets are more susceptible to impact-triggered atmospheric loss. For planets where the heat capacity of the core is much greater than the envelope’s heat capacity (envelope mass fractions ≤4 percent), the impactor mass required for significant atmospheric removal is Mimp / Mp ∼ μ/μc ∼ 0.1, approximately the ratio of the heat capacities of the envelope and core. Conversely, when the envelope dominates the planet’s heat capacity, complete loss occurs when the impactor mass is comparable to the envelope mass. Because of their stochastic nature, giant impacts may provide a natural explanation for the observed range of super-Earth and mini-Neptune densities.
Caroline Dorn (Zurich) – The Diversity of Super-Earths and a New Super-Earth-class Formed from High-temperature Condensates [Presented by Apurva Oza]
Super-Earths do not follow a simple mass–radius trend, but rather reveal a diversity
of mass–radius relationships that are usually associated with compositional and structural differences. We hypothesise that differences in the temperatures at which rocky material condensed out of the nebula gas can lead to differences in the composition of key rocky species (e.g.,Fe, Mg, Si, Ca, Al, Na) and thus planet bulk density. Such differences in the observed bulk density of planets may occur as a function of radial location and time of planet formation. In this talk we show that the predicted differences are on the cusp of being detectable with current instrumentation. In fact, for HD 219134, the 10 % lower bulk density of planet b compared to planet c could be explained by enhancements in Ca, Al rich minerals. However, we also show that the 11 % uncertainties on the individual bulk densities are not sufficiently accurate to exclude the absence of a density difference as well as differences in volatile layers. Besides HD 219134 b, we demonstrate that 55 Cnc e and WASP-47 e are similar candidates of a new Super-Earth class that have no core and are rich in Ca and Al minerals which are among the first solids that condense from a cooling proto-planetary disc. Planets of this class have densities 10-20% lower than Earth-like compositions and may have very different interior dynamics, outgassing histories and magnetic fields compared to the majority of Super-Earths.
10 AM — Coffee Break
10:30 AM — Poster Viewing Session with Lunch (food served at 11:30 AM in Floi poster area)
Free Afternoon and Evening
THURSDAY
8:30 AM — Atmospheres – I [Chair: Caroline Morley]
Laura Mayorga (Harvard-Smithsonian CfA) – The Galilean Satellites Observed by Cassini: A Testbed for Icy Terrestrial Exoplanets
For terrestrial exoplanets with thin atmospheres or no atmospheres, the surface will dominate to the reflected light signal of the planet. Direct observation of the disk-integrated brightness of bodies in the Solar System, and the variation with illumination angle, wavelength, and planetary longitude, is essential for both planning imaging observations of exoplanets and interpreting the eventual datasets. We will present our analysis of approximately 5,000 Cassini observations of the Galilean satellites through an exoplanet lens and show their longitudinal and illumination variations. The data span a range of wavelengths from 400-950 nm and predominantly phase angles from 0-25 degrees with some constraining observations near 120 degrees. Restricted to observations at the same illumination angle, we show that we can clearly detect the spin period of each of the four moons. We invert these light curves to reconstruct maps of the surfaces and we present comparisons of these maps to direct images. In the case of Io, we detect a clear color variation that can be traced to geologic features with varying quantities of sulfur compounds and silicates across the surface. Despite the similarity in size and density between the moons, surface inhomogeneities result in significant changes in the disk-integrated reflectivity with planetocentric longitude and phase angle. This implies that future exoplanet observations could exploit this effect to deduce surface variations, determine rotation periods, and potentially infer surface composition. Furthermore, the Galilean satellites are all distinctly non-Lambertian with steep phase functions, implying that icy exoplanets will be fainter than expected at quadrature and more demanding to characterize by direct imaging.
Ruth Murray-Clay (UC Santa Cruz) – Prospects for Using H-alpha Transits to Probe Escaping Atmospheres
The recently-observed dearth of super-Earths with radii ~1.8 times that of Earth is a member of a rare class of discoveries: observational confirmation of a clear theoretical prediction. Two separate groups predicted this feature using models of photoevaporative atmospheric loss. Since the discovery of the super-Earth radius gap, these models have been used to constrain properties of this planetary population such as the core mass distribution, with exciting results. As the quantitative results of photoevaporation models become more important (and as photoevaporation is compared to core-powered mass loss, a new competing theory for the source of energy driving escape), improved observational constraints on photoevaporation models are sorely needed. I will present new results showing that, though transits in hydrogen’s H-alpha line have thus far provided limited information about escaping atmospheres, for thoughtfully-chosen planetary samples, this line has exciting potential. Most direct observations of photoevaporation in action have been conducted using transits in hydrogen’s Lyman-alpha line. Because this line’s center is obscured by ISM absorption, these observations primarily provide information about outflowing gas far from the planet, making mass loss rate calculations model dependent. For most planets currently observed to have escaping gas, the fraction of escaping hydrogen in the n=2 state is too small for significant H-alpha absorption. I will present new theoretical calculations showing that for planets experiencing a larger XUV flux, recombination cascades can populate the n=2 state at an observable level. I will comment on these results in the context of A-stars such as Kelt 9, flaring M-stars, and young stars, and attempt to convince conference attendees that additional observational campaigns are warranted in the conveniently accessible from the ground H-alpha line.
Björn Benneke (Montreal) – A Sub-Neptune Exoplanet with a Low-Metallicity Methane-Depleted Atmosphere and Mie-Scattering
The discovery of thousands of exoplanets with masses and radii intermediate between Earth and Neptune was one of the biggest surprises of exoplanet science. These super-Earths and sub-Neptunes likely represent the most common outcome of planet formation. Mass and radius measurements indicate a diversity in bulk composition much wider than for gas giants; however, direct spectroscopic detections of molecular absorption and constraints on the gas mixing ratios have largely remained limited to planets more massive than Neptune. In this talk, we present the main results from an unprecedented HST/Spitzer data set (12 transits and 20 eclipses) of a sub- Neptune exoplanet, whose mass of 12.6 Earth masses places it near the half-way point between previously studied exo-Neptunes (22-23 Earth masses) and exoplanets known to have rocky densities (7 Earth masses). Obtained over many years, our data set provides a robust detection of water absorption (> 5 sigma) and a thermal emission detection from the lowest irradiated planet to date. We reveal a low-metallicity, hydrogen-dominated atmosphere similar to a gas giant, but strongly depleted in methane gas. The low, near-solar metallicity (O/H=0.2-18) sets important constraints on the potential planet formation processes at low masses as well as the subsequent accretion of solids. The low methane abundance indicates that methane is destroyed much more efficiently than previously predicted, suggesting that the CH4/CO transition curve has to be revisited for close-in planets. Finally, we also find a sharp drop in the cloud opacity at 2-3 μm characteristic of Mie scattering, which enables narrow constraints on the cloud particle size and makes the planet a keystone target for mid-IR characterization with JWST.
Maggie Thompson (UC Santa Cruz) – Meteorite Outgassing Experiments to Inform Chemical Abundances of Super-Earth Atmospheres
At present, there is no first-principles understanding of how to connect a terrestrial planet’s bulk composition to its atmospheric properties. Since terrestrial exoplanets likely form their atmospheres through degassing (Elkins-Tanton & Seager 2008), a logical first step to build such a theory for super-Earths is to assay meteorites, the left-over building blocks of planets, by heating them to measure the outgassed volatiles. Our Solar System presents a wide variety of meteorite types, including chondrites which are primitive unaltered rocks believed to be representative of the material that formed the rocky planets. We present the current results of our meteorite outgassing experiments in which we heated a variety of chondritic meteorite samples, at carefully controlled rates to temperatures from 200 to 1200 °C and measured the partial pressures and relative abundances of the outgassed volatile species (e.g., CO2, H2O, CH4, H2, O2, S, Na) as a function of temperature and time. Our experimental set-up consisted of a residual gas analyzer connected to a furnace to heat samples at specified rates. We compare the results of these experiments to Schaefer and Fegley’s prior theoretical chemical equilibrium and kinetics calculations which modeled thermal outgassing for a wide variety of chondrites to predict the composition of terrestrial atmospheres formed via outgassing of specific types of meteorites (Schaefer & Fegley 2007, Schaefer & Fegley 2010). In addition to testing and validating Schaefer and Fegley’s models, the results from our experiments inform the phase space of chemical abundances used in atmospheric models of super-Earth exoplanets.
Wilson Cauley (UC Boulder) – Magnetic Fields of Hot Jupiters Calculated from Star-planet Interactions
Planetary magnetic fields have a critical impact on atmospheric physics, damping winds on hot, shortperiod planets and potentially creating the necessary conditions for habitability on temperate terrestrial worlds by deflecting stellar wind particles. Despite their importance, exoplanet magnetic field detections remain elusive. For the first time, we report the derivation of the magnetic fields of a sample of hot Jupiters using flux-calibrated signals of magnetic star-planet interactions (SPI). We find that the surface magnetic field values for the hot Jupiters in our sample range from 20 G to 120 G, 10 – 50 times larger than the values predicted by pure dynamo theories for planets with rotation periods of 2 to 4 days. Such large field strengths should have severe consequences for velocity flows in the planets’ atmospheres and exhibit peak frequencies of electron-cyclotron emission in the range of facilities such asLOFAR.
Leslie Rogers (U Chicago) – Helium-enhanced Planets at the Edge of the Radius Gap
Primordial hydrogen-helium envelopes surrounding sub-Neptune-sized planets are susceptible to mass loss driven by ionizing radiation from their host star. The effect of mass loss is imprinted on observed exoplanet populations in the form of a “photo-evaporation desert” and a “gap” at 1.6 Earth Radii in the planet radius distribution. To date, models of the mass-loss evolution of exoplanets have assumed that the planetary envelope composition stays constant over time. However, after an initial ~0.1 Gyr phase of rapid hydrodynamic mass loss, sub-Neptunes may experience a subsequent phase of thermal escape modulated by diffusive separation between hydrogen and helium wherein they gradually become enhanced in helium and metals (relative to hydrogen) over billions of years. We predict that planets on the large radius edge of the “radius gap” in planet occurrence rates could be significantly enhanced in helium (or depleted in hydrogen) relative to solar composition. We have performed the first self- consistent calculations of the coupled thermal, mass-loss, and compositional evolution of hydrogen-helium envelopes surrounding sub-Neptune mass planets. Our simulations consistently produce planets with envelope helium mass fractions in excess of Y=0.5 (at planet ages of 5 Gyr) near the upper edge of the radius gap. Our results have important implications for the interpretation of atmospheric transmission and emission spectra of low- density sub-Neptune-size planets, which are prime targets for atmospheric characterization with HST and eventually JWST. Enhancement in helium relative to hydrogen will affect both the scale height and equilibrium chemical abundances in the atmosphere (e.g., CO relative to CH4). To date, most atmospheric retrieval analyses have fixed the ratio of hydrogen and helium to solar abundances; this assumption must now be relaxed. Our prediction further provides a new observational test for the extent to which the radius gap is caused by atmospheric mass loss versus an intrinsically bimodal outcome of planet formation.
10 AM — Coffee Break
10:30 AM — Population Statistics and Mass-Radius Relations [Chair: Diana Valencia]
Benjamin Fulton (Caltech/IPAC) – Frequency of Gaseous Planets Beyond the Ice Line
The occurrence distribution of long-period planets is a key unknown left in our understanding of exoplanetary demographics. The presence of Jupiter and Saturn in our solar system likely facilitated the formation of Earth and the other terrestrial planets, yet we do not have a clear picture of the intrinsic frequency of gas giant planets orbiting beyond ∼5-10 AU in exoplanetary systems. Here we analyze a massive dataset of over 35,000 archival Keck/HIRES and Lick radial velocities collected over the past 30 years for a sample of 785 nearby stars. This groundbreaking study provides direct measurements of the mass, period, and eccentricity distributions of Jupiter and Saturn-mass planets beyond 5 AU and Neptune-mass planets out to the location of the ice line (∼3 AU for sun-like stars). We are finally able to unify, compare and contrast planet population statistics from direct imaging surveys with those of radial velocity and transit surveys. This will have a profound impact on the planning of future direct imaging campaigns, potentially providing them with targets to observe and yield predictions. We examine the period distribution of gas giant planets beyond 10 AU to look for the fall off in the planet occurrence rate required to reconcile the tension between radial velocity studies and direct imaging studies. We measure the mass distribution of Neptune to Jupiter mass planets orbiting beyond 3 AU to look for an enhancement in the frequency of sub-Jovian planets near the ice line as is observed for Jovian and super-Jovian mass planets. We compare the mass-distribution of planets beyond 3 AU to those orbiting inside 1 AU to look for the signatures of planet migration and shepherding of the multitude of small, low-mass planets discovered by Kepler. The results of this study will have profound impact on the planning of future direct imaging campaigns, potentially providing them with targets to observe and yield predictions. By connecting the regimes of exoplanetary demographics explored by all of the various detection techniques we provide a unified view of the end product of planet formation across the entire protoplanetary disk.
Dave Latham (Harvard-Smithsonian CfA) – Masses and Radii of Exoplanets from Kepler, K2, and TESS
The population of planets orbiting solar-type stars is dominated by planets smaller than 4 Earth radii, the size of Neptune. Mass determinations for transiting planets identified by Kepler and K2 have suggested that most planets smaller than about 1.8 Earth radii have bulk densities that are consistent with internal structures and compositions similar to the terrestrial planets in the Solar system. One of the primary goals of the TESS mission is to determine masses and bulk densities for more than 50 planets smaller than 4 Earth radii, to improve our understanding of the transition between rocky planets and those more like Neptune. We will highlight the progress towards meeting that goal.
Didier Queloz (Cambridge) – On the Hunt for Trappist-1 Siblings
The TRAPPIST-South 60cm telescope at La Silla (ESO) is famously known for its detection of the extraordinary TRAPPIST-1 planetary system. A discovery made during the prototype phase of our ultra-cool dwarf transit survey SPECULOOS (Search for Planets EClipsing ULtra-cOOl Stars). This talk will first report on the self-consistence transit occurrence analysis of all observations of 42 bright ultra-cool dwarfs made with TRAPPIST-South during a period ranging from 2011 to 2017. On the basis that, with the exception of the discovery of TRAPPIST-1 planets, we didn’t detect any other significant transiting event, we concluded on a 10% lower limit for the occurrence of planets similar to TRAPPIST-1b in this sample. The outcome is very sensitive to the size and period of the planet considered. A comprehensive statistic will be presented. Finally, performance obtained with our recently commissioned SPECULOOS Southern facility installed at Paranal will be presented. The lower occurrence limit measured with TRAPPIST survey will be compared with early results from 6 months of continue SPECULOOS core survey operations
Malena Rice (Yale) – ‘Oumuamua and DSHARP Point to 10^11 Hidden Planets
The discovery of the first interstellar asteroid, ‘Oumuamua, strongly suggests an enigmatic abundance of free-floating asteroids whose ejection into galactic space is entirely unexplainable by the current population of known exoplanets. Remarkably, it signals the existence of a vast undiscovered population of wide-separation (~5+ AU) planets of Neptune’s size or larger that are capable of directly ejecting debris from their environments. The ALMA Disk Substructures at High Angular Resolution Project (DSHARP) recently returned 20 ultra high-resolution images of protoplanetary disks, illustrating a ubiquity of substructures among the protoplanetary disk population. We present new results demonstrating for the first time that the planets suggested by radial gaps in the DSHARP sample are consistent with the undiscovered exoplanetary population required to produce a significant flux of interstellar objects. There are a number of compelling near-term prospects for detecting the population of planets that we have inferred, with which we conclude.
Lauren Weiss (Hawaii) – Peas in a Pod: Planets in Kepler’s Multiplanet Systems are Similar in Size and Regularly Spaced
As part of the California Kepler Survey, we have established precise planet radii, semimajor axes, incident stellar fluxes, and stellar masses for 909 planets in 355 multi-planet systems discovered by Kepler. In this sample, we find that planets within a single multi-planet system have correlated sizes: each planet is more likely to be the size of its neighbor than a size drawn at random from the distribution of observed planet sizes. In systems with three or more planets, the planets tend to have a regular spacing: the orbital period ratios of adjacent pairs of planets are correlated. Furthermore, the orbital period ratios are smaller in systems with smaller planets, suggesting that the patterns in planet sizes and spacing are linked through formation and/or subsequent orbital dynamics. The regular sizes and spacing of the Kepler planets are among the most common outcomes of planet formation, suggesting that our solar system is not among the majority of planetary system architectures. New theories of planet formation might be required to reproduce the patterns in the Kepler planetary systems.
Wei Zhu (CITA) – Planets Do Not Show Intra-system Uniformity
Recent works claim that planets in the same system should have similar properties (namely, mass and radius) and be regular spaced. These patterns, if true, would have significant implications for theories of planet formation and evolution. In this talk, I will show that this so-called intra-system uniformity can be largely, if not entirely, explained by detection biases. The universal signal-to-noise threshold that is used in Kepler transit detections corresponds to different thresholds in planetary parameters for different stars. I will show that it is this variation in detection threshold that is responsible for the majority of the claimed correlation in planet properties. With a more robust statistical approach, I find that the presence and the size of the smaller planets is independent of the presence and size of their largest sibling, arguing against the so-called “intra-system uniformity.” Theoretical implications of these findings will also be discussed.
Yanqin Wu (Toronto) – Kepler Planets: A Uniform Population
In this talk, I will discuss recent progress regarding the masses of Kepler planets, and how they seem to make up a surprisingly uniform population.
This uniformity is unpredicted, and challenges theories of planet formation. As an aside, Kepler planets appear to have interesting connections to the formation of stellar binaries.
Lunch Break
2:00 PM — Planets in and around Binaries [Chair: Smadar Naoz]
Clémence Fontanive (Edinburgh) – The Role of Stellar Multiplicity in the Formation of Massive Close-In Giant Planets and Brown Dwarfs
Stellar multiplicity is believed to influence planetary formation and migration, although the precise nature and extent of this role remain ambiguous. In this talk, I will present new results from a survey aimed at testing the impact of stellar multiplicity on the formation and/or evolution of the most massive, close-in planetary and substellar companions, which are extremely challenging to explain with current theoretical models. Using direct imaging observations and the Gaia DR2 catalogue, we searched for wide binary companions to stars hosting massive giant planets or brown dwarfs (M > 7 MJup) on orbits shorter than ~1 AU. From a robust statistical analysis, we derived a very high binary fraction of ~80% on separations of 20–10,000 AU for our sample, twice as high as for field stars with a 3-σ significance. These results indicate that stellar companions greatly influence the formation or evolution of these systems. This binary frequency was also found to be larger than for lower-mass planets on similar orbits, suggesting that the effects of binary companions become more important for higher-mass planets. Our survey thus demonstrates that binarity plays a crucial role in the existence of very massive short-period giant planets and brown dwarf desert inhabitants, almost exclusively observed in multiple systems. These new results provide vital information and constraints for both theoretical studies of planet formation, and observational campaigns of exoplanets and brown dwarf companions.
Ian Czekala (UC Berkeley) – The Mutual Inclinations of the Proto-Tatooine Disks
Efforts to learn about the efficiency of circumbinary planet formation from the dozen circumbinary systems discovered by Kepler are hampered by the fact that the occurrence rate is degenerate with the underlying mutual inclination distribution (i.e., the typical misalignment between the binary and planetary orbital planes). In this talk, I will discuss our survey of 20 spatially-resolved circumbinary protoplanetary and debris disks, which includes several spectroscopic binaries (P < 40 days) whose disks we have resolved with ALMA for the first time. Crucially, these tight binaries are the only protoplanetary systems that are comparable in scale to the Kepler circumbinary planet hosts. Using a hierarchical Bayesian model, we infer that the disks around short-period binaries are intrinsically coplanar (< 5° mutual inclination), implying that the occurrence rate of Kepler circumbinary planets is similar to that around single stars (∼10% for planets with radii ∈ [4,10] REarth). In stark contrast, however, the mutual inclinations of slightly wider binary systems (P > months) are much more varied: there are several strongly misaligned disks (> 40°), with even a few circumpolar disks (90°) around highly eccentric (e > 0.7) binaries. We will demonstrate that a combination of tight binary star formation mechanisms and high eccentricity oscillatory effects can explain the extremely strong trends of mutual inclination with binary period and eccentricity.
Bill Welsh (San Diego State) – Circumbinary Planets at the K/T (Kepler-TESS) Boundary
Eight years ago at the ESS II conference, we presented the first Kepler circumbinary planets. Since then, 11 planets in 9 systems have been discovered. In this talk we present the last two unpublished, unambiguous Kepler transiting circumbinary planets: KOI-3152 and KIC 10753734. Both systems have planets with rapidly precessing orbits and significantly spotted stars which has made their characterization difficult. The orbital periods are 28.2 and 19.4 days for the binaries, and 171 and 260 days for the planets, respectively. In both systems three transits were detected, yielding planetary radii of 3.4 and 6.0 Re. Like most of the circumbinary planets, these planets orbit near the binary (in)stability radius. KOI-3152 is a particularly interesting case: its eclipses are extremely grazing (impact parameter > 1) and thus its eclipse depths and widths are extremely sensitive to changes in the orbital inclination. A change in inclination is in fact detected, and can be modeled as the result of precession driven by a ~140 Me planet. But this mass is not consistent with the planet’s 3.4 Re radius – something is wrong. After much scrutiny, we have solved the problem: The increasing eclipse depth is spurious – it is the result of increasing starspot coverage that has led to an incorrect out-of-eclipse flux normalization. This well-understood (though ignored) bias is of course not particular to binary stars. But the change in the bias is pernicious. We will put these two new planets in context and briefly discuss what the ensemble of Kepler transiting circumbinary planets has to offer exoplanet science: the most accurately known masses and radii, challenges to understanding planet formation and migration, revising the definition of the habitable zone, and why circumbinary planets are often more suitable for life than single-star planets. Finally, we close with a mention of how TESS is expected to reveal hundreds of new circumbinary planets via the “one-two punch” discovery technique, and how we are on the cusp of transitioning from detailed characterization of a handful of planets to being able to carry out statistical studies of the circumbinary planet population.
2:45 PM — Planets around White Dwarfs [Chair: Steinn Sigurdsson]
Christopher Manser (Warwick) – A Planetesimal Orbiting within the Debris Disc around a White Dwarf
I will present the first and so far only spectroscopically detected planetesimal around a white dwarf (Manser et al. 2019, Science, 364, 66). The body orbits within a disc of rocky debris on a period of 2.06 hours, making it the closest planetary body to a white dwarf. To withstand the tidal forces this deep in the gravitational field of the white dwarf this planetesimal must have some internal strength and/or a high density, and I discuss the possibility of it being the core of a differentiated planet that has partially disintegrated. During the talk, I will highlight the methods used to make the discovery, how I can apply this newly developed method to several other white dwarf systems, and how these extreme bodies could explain the presence of gaseous debris discs at white dwarfs.
Matthias Schreiber (U Valparaiso) – Gas Giant Planets Evaporated by Hot White Dwarfs
All known exo-planet hosts stars will evolve into white dwarfs. It is well established that many white dwarfs are accreting small planetary bodies, including asteroids and comets, indicating that planetary systems survive, at least in part, the metamorphosis of their host stars. Gravitationally scattering planetesimals towards the white dwarf requires the presence of more massive bodies, yet no planet has so far been detected at a white dwarf. We discovered a moderately hot white dwarf that is accreting from a circumstellar gaseous disc composed of hydrogen, oxygen, and sulphur. The composition of the disc is unlike all previously detected gaseous disks around white dwafs but resembles predictions for deeper atmospheric layers of icy gas giants, with H2O and H2S being major constituents. We therefore suggest that a gas giant orbiting the white dwarf is evaporated by the strong EUV irradiation from the hot white dwarf. While still indirect, this discovery represents the so far clearest evidence for the expected existance of gas giant planets around white dwarfs. We extend on this result by calculating the orbital separation at which gas giant planets will be evaporated by hot white dwarfs. We find that planets such as the gas giant planets in our solar system are expected to be located at such separations from the sun when it completed its metamorphosis into a white dwarf.
Amy Steele (U Maryland) – The Abundances of Metals in Circumstellar Gas around Polluted White Dwarfs
Between 30 – 50% of white dwarfs (WDs) show heavy elements in their atmospheres. This “pollution” likely arises from the accretion of planetesimals that were perturbed by outer planet(s) into the white dwarf’s tidal radius. A small fraction of these WDs show either emission or absorption from circumstellar (CS) gas. For example, high resolution spectroscopic observations of WD1145+017 reveal photospheric and CS absorption lines of elements heavier than helium in multiple transitions. The photospheric abundances have been measured and are similar to the bulk composition of the Earth. The CS component arises from a gas disk produced through the sublimation of a transiting, disintegrating planetesimal. Models (to date) have not yet been able to link the CS species to the total atomic abundance in gas. Here we present self-consistent models of CS gas in orbit around various types of WDs and demonstrate how we determine the abundances of CS lines arising from planetesimals. Additionally, we build a grid of models to place constraints on the gas masses needed for detection of CS gas around various WDs with current observatories. We test the grids using new discoveries and WDs with previously known CS gas, in preparation for constraining the frequency of CS gas around statistical samples of WDs. Knowing the abundances of CS gas around polluted white dwarfs will provide a key to understanding the instantaneous composition of the material accreting onto the photosphere and will allow a direct comparison to the composition of rocky bodies in the Solar System.
3:30 PM — Coffee Break
4:00 PM — Atmospheres – II [Chair: Jayne Birkby]
Vincent Bourrier (U Geneva) – The Most Extreme Case of Atmospheric Escape Detected on the Warm Neptune GJ 3470b with HST
Observations of exoplanets during the transit of their host star allow probing the structure and composition of their atmosphere. The intense stellar energy input into exoplanets orbiting close to their star can lead to a dramatic expansion of their upper atmosphere, and the ‘evaporation’ of large amounts of gas into space. UV observations of hot Jupiters revealed the extended exospheres formed by this escaping gas, and showed that these planets are too massive to lose a substantial fraction of their atmosphere. Lower-mass planets are expected to be much more sensitive to evaporation, which has long been thought to play a role in forming the desert of hot Neptunes (a deficit of Neptune-size exoplanets on very short orbits). I will present the discovery of a giant hydrogen exosphere around GJ3470b, a warm Neptune located at the border of the desert. This is the first UV result of the Panchromatic Comparative Exoplanet Treasury (PanCET) survey, a Hubble program targeting 20 exoplanets across the entire spectrum. Our numerical simulations of the resolved exospheric transit show that GJ3470b is subjected to mass losses comparable to that of hot Jupiters, making it the most extreme case of evaporation observed to date. GJ3470b could already have lost up to 40% of its mass over its 2 Gyr lifetime, bringing direct observational confirmation that evaporation shaped the population of close-in exoplanets. I will compare GJ3470b with other known evaporating planets and discuss the reasons for its dramatic escape. Our results strengthen the interest of observing the upper atmosphere of exoplanets to determine their properties and understand how they depend on their past evolution. This is particularly important for super-Earth and Earth-size planets, whose lower atmosphere could be hidden by clouds. The development of new tracers of atmospheric escape at optical/infrared wavelengths opens thrilling perspectives for the characterization of exoplanets via their upper atmosphere.
Ian Crossfield (MIT) – Infrared Eclipses and Transits of the Best TESS Planets
A key TESS goal is to identify the best exoplanet targets for atmospheric study. We will report on initial results from our large-scale Spitzer program to follow up TESS planets with mid-infrared transits and eclipses. Spitzer’s unparalleled infrared sensitivity and photometric stability are allowing us to refine the properties of these new planets and ensure that their transits and eclipses can be recovered for many years to come — e.g., with HST and JWST. Our program focuses on the smaller (i.e., sub-Jovian) planets for which ground−based observations are impractical and for which JWST spectroscopy will have a high impact. Our most exciting results will include the only secondary eclipse measurements of these sub- Jovian planets until JWST launches. Our program includes eclipse observations of planets from 1–6 Earth radii and equilibrium temperatures from 800-2500 K. In addition, we are producing some of the only thermal phase curves known for such planets. Our program is providing the touchstone sample of TESS planets that will be studied in great detail for many years to come.
Katelyn Allers (Bucknell U) – A Novel Method for Measuring Wind Speeds on Exoplanets and Brown Dwarfs
Within our solar system, we can directly observe the effects of rapid rotation on the atmospheric physics of the giant planets. Zonal winds, a result of rapid rotation and convection, play an important role in the bulk atmospheric flow. This, in turn, can impact atmospheric chemistry, as evidenced by Jupiter’s disequilibrium PH3, which dominates its mid-IR spectrum. Similar to Jupiter and Saturn, recent studies reveal that many brown dwarfs and directly-imaged exoplanets are also fast rotators with evolving atmospheric inhomogeneities. The effects of rotation and convection are starting to be included in efforts to model the atmospheric dynamics of brown dwarfs and exoplanets. The resulting predictions of wind speed, however, remain relatively untested.
We present the first results of a novel new method for measuring wind speeds on exoplanets and brown dwarfs. Utilizing a combination of radio observations and infrared photometric variability, we present the first observational constraints on wind speed for a cool, cloudless brown dwarf. We discuss the implications of our measurement for models of atmospheric circulation. Looking to the future, we discuss the ways in which new observational facilities could extend our method of wind speed measurement to other brown dwarfs and exoplanets.
Enric Palle (Canarias) – Exoplanet Atmospheres at High Spectral Resolution with CARMENES
Transmission spectroscopy using high-resolution spectrographs is quickly becoming a major tool to detect and understand planetary atmospheres, from ultra hot Jupiters to Neptunes-size planets. The CARMENES spectrograph started operations in 2016, and since then we have been using it for the study of planetary atmospheres taking advantage of it simultaneous wavelength coverage from visible to near-infrared (0.5-1.7 micron). This has led to several innovative results, including the first ground-based detections of the He I triplet, allowing the study of exoplanetary tales and scape ratios, or the detection for the first time of the Ca triplet (together with FeII, Na I, and the Balmer series of Hα, Hβ, and Hγ) in the atmosphere of the ultra hot Jupiter (UHJs) MASCARA-2b/KELT20-b. In this talk we will update the several He detections on a sample of about a dozen planets, including various levels of stellar irradiation and planetary masses. I will also discuss CARMENES’s capabilities for the characterization of UHJs atmospheres, where our results are consistent with theoretical models, predicting a rich day-side ionosphere. For the SOC: The CARMENES team as a large sample of exoplanets observed (some published some not yet), which can for the first time provide correlations between stellar irradiation and the detectability of He I triplet and Halpha lines, in some cases both, useful for both observers and modelers. I can review the overall results, currently in preparation for a number of publications. For UHJ atmospheres, we can detect several atmospheric species with both trasnmission spectroscopy and cross-correlation techniques simultanoeuly, again for a sample of hot planets. So I think this talk will nicely summaryze several results in two important hot topics of exoplanet atmospheres.
Nikole Lewis (Cornell) – Unlocking the Hidden Secrets of Hot Jupiter Atmospheres through Near-Ultraviolet Spectroscopy: A Case Study of HAT-P-41b
Near-Ultraviolet (NUV, 200-400 nm) spectra of planets hold rich information about the chemistry and physics at work in their upper atmospheres. In the solar system, NUV spectroscopy has been critical in identifying and measuring the abundances of a variety of hydrocarbon and sulfur-bearing species, produced via photochemical mechanisms, as well as oxygen and ozone. To date, less than 20 exoplanets have been probed in this critical wavelength range, with mixed results, limited by the wavelength coverage and sensitivity of the workhorse instrument for such studies, HST’s STIS G430L and E230M gratings. In HST Cycle 25, our team embarked on a journey to explore the potential of HST’s WFC3/UVIS G280 grism, which offers the highest throughput of all HST’s instruments in the NUV and is up to 25 times more sensitive than its STIS counterparts at 350 nm. The WFC3/UVIS G280 grism does offer one challenge, the presence of overlapping spectral orders similar to those of JWST’s NIRISS instrument, which required us to develop new data reduction and analysis techniques. The first target to be explored with this newly unlocked mode on HST was the hot Jupiter HAT-P-41b, which had been previously observed with HST’s STIS G430L grism. Our high-precision spectrum of HAT-P-41b, which combines information from both the positive and negative spectral orders, has revealed features in the NUV that cannot be explained by standard equilibrium chemical models, the presence of aerosols, or stellar activity. Drawing on solar system and stellar studies, we considered dozens chemical species that are known to absorb strongly at NUV wavelengths. Through detailed atmospheric modeling and retrieval analyses we have uncovered not yet considered chemistry and physics at work in the atmosphere of HAT-P-41b, which is likely present in many exoplanet atmospheres. In this talk I will detail the opportunities that have been opened up with the HST WFC3/UVIS G280 grism in the exploration of exoplanet atmospheres and reveal the once hidden secrets of HAT-P- 41b’s atmosphere.
Caroline Morley (UT Austin) – New Theoretical Models for Cloudy Substellar Atmospheres
Ample evidence suggests that exoplanets of all kinds have clouds, likely made of many different materials from refractory minerals, to silicate dust, to salts, to volatile ices. Clouds are complex to model and challenging to understand from limited observations of exoplanets. Fortunately, planet-mass free-floating objects provide a key venue for understanding cloud formation in substellar atmospheres. These objects have the temperatures of planets but, critically, lack a nearby star, making high signal-to-noise, high precision measurements possible. To understand the physics and chemistry of these atmospheres, we need to compare these high fidelity observed spectra to state-of-the-art models. Recent improvements to the ingredients in substellar atmosphere models include new line lists for various important species (methane, alkali metals, water, etc.), as well as updated chemistry calculations for a range of metallicities and carbon-to-oxygen ratios. Here, we present a new set of substellar atmosphere models for objects warmer than 1000 K including clouds. We show how these models differ from previous cloudy brown dwarf models (Saumon & Marley 2008), and demonstrate how metallicity affects cloudy substellar spectra. We present results comparing these models to field brown dwarfs, free-floating planets, and directly-imaged companions, demonstrating how gravity changes cloud properties and emergent spectra. Finally, we present a new technique for understanding the compositions and mineralogy of clouds in brown dwarfs using mid-infrared spectroscopic time-series measurements with JWST. These models will publicly available and provide a critical tool for the community in the lead-up to the launch of JWST.
Mathias Nowak (Obs. Paris) – Peering into the Formation History of Beta Pic b with Long-baseline Interferometry
Beta Pictoris is arguably the best-known stellar system outside of our own. 30 years of study have revealed a highly structured circumstellar disk with rings, belts, and a giant planet. But very little is known about how it came into being. In particular, the giant planet beta Pictoris b is known to have played a crucial role in the structuring of the system, but its formation history remains elusive, despite some attempts to settle the cold / hot start question. I will present the first interferometric observations of the giant planet Beta Pic b, obtained with GRAVITY, on the combined four 8.2 m telescopes of the VLTI. These observations resulted in the cleanest (S/N > 50), medium resolution (R=500), K-band spectrum of a giant planet ever obtained. I will show that this spectrum, combined with existing low-resolution data, can be used to estimate the planetary C/O ratio, which in turn can be used to trace down the formation history of the planet. In particular, I will present two interpretations of the low C/O ratio obtained, one in the gravitational collpase formation paradigm for planet formation, and one in the core-accretion paradigm.
7:00 PM — Conference Dinner at Perlan
FRIDAY
8:30 AM — Atmospheres – III [Chair: Nick Cowan]
Brittany Miles (UC Santa Cruz) – Non-equilibrium Chemistry of the Coolest Brown Dwarfs: Implications for Directly Imaged Exoplanets
The Y-dwarf spectral class is composed of only ~23 brown dwarfs with effective temperatures below 450 K and atmospheres rich in gaseous methane, ammonia, and water. Y-dwarfs are colder than any current directly imaged exoplanet, offering previews into the atmospheric physics of gas giants that will be discovered and characterized in the future with JWST and SCALES. The coldest brown dwarf WISE 0855 (250 K) showed water absorption and evidence of clouds across its M-band (4.5 – 5.0) spectrum. In addition to this, WISE 0855 is also only ~100 K hotter than Jupiter, yet its lack of phosphine absorption means that it has significantly different atmospheric mixing properties than Jupiter. This difference implies that there could be a large degree of variation in atmospheric physics at extremely cool temperatures. In this work, we expand the sample of cool brown dwarf M-band spectra to cover the temperature range of 250 K – 700 K by taking low resolution Gemini/GNIRS spectra of 4 T/Y-dwarfs (50 hours, WISE 1541, WISE 2056, WISE 0313, UGPS 0722) and placing them in context to previously published spectra (WISE 0855, 2MASS 0415, Gl 570D). With the exception of Gl 570D, cloud-free, solar metallicity brown dwarf models do not accurately fit the spectral slopes of our sample and better fits are achieved when non-equilibrium abundances of carbon monoxide are added into the atmospheric models. Atmospheric mixing can bring up warmer carbon monoxide gas and our sample suggests that mixing becomes stronger at cooler effective temperatures. We discuss why these types of atmospheric analyses are essential for 1) planning and interpreting higher quality JWST Y-dwarf observations and 2) predicting what may be observable on cooler, low-gravity gas giant exoplanets.
Jean-Michel Désert (U Amsterdam) – New signatures of Planet Formation Scenario in Gas Giant Exoplanet Atmospheres [Presented by Lorenzo Pino]
We present a portfolio of observational projects for which we have recently succeeded in measuring the atmospheric composition and metallicities of gas giant exoplanets. We study the atmospheric properties of giant exoplanets over a broad range of masses and equilibrium temperatures, and retrieve their their chemical and dynamical properties. We introduce novel observational techniques and diagnostics to probe exoplanet atmospheres and climates of tidally locked planets; we measure their composition at different longitudes, from their dayside to their nightside, and with multiple spectral resolution. These projects use diverse and complementary approaches to retrieve atomic and molecular abundances and the atmospheric metallicity, including new metallicity tracers (e.g. alkali metals, iron, hydrides). We present the breakthrough results but also the main challenges to overcome while making these measurements. When combined together, our findings on the measurements of atmospheric metallicity allow us to make quantitative comparisons amongst exoplanets, and with the Solar System planets, in order to test predictions from planet formation models. The first results from these projects offer the tantalizing suggestion that some of the trends seen in the Solar System are also seen in extrasolar systems, but others are not. Ultimately, I will present the implication of these new results in the context of exoplanets, and shed light on our understanding of exoplanets’ formation, evolution and architectures.
Jens Hoeijmakers (U Bern) – Heavy and Rare-earth Metals in the Transmission Spectra of Ultra-hot Jupiters
Ultra-hot Jupiters form a new class of exoplanets that tend to orbit hot early type stars in short periods. The first Ultra-hot Jupiter known to exist is KELT-9 b: A massive gas giant heated to a temperature of over 4,000K on the day-side by its 10,000K A-star. The extreme temperature dissociates all but traces of the most strongly bound molecules (CO and H2O) into their constituent atoms. A significant fraction of the atomic gas is thermally ionised. Under these circumstances, line absorption lines by metals and continuum absorption by the hydrogen anion are the dominant sources of opacity. Clouds and aerosols are notably absent, and the timescales of chemical reactions are much shorter than those of mixing and photo-ionisation over most of the atmosphere at the day-side and terminator regions. This means that the interpretation of the transmission spectrum of KELT-9 b should be greatly simplified compared to planets for which aerosols and non-equilibrium chemistry are important. We recently performed a survey of the transmission spectrum of KELT-9 b as observed with the high-resolution HARPS-N spectrograph and discovered multiple heavy metals, including iron, chromium, scandium and yttrium. We find that the absorption lines of neutral iron are almost perfectly predicted by a model of an isothermal atmosphere in hydrostatic and chemical equilibrium, but that all other lines are anomalously strong, indicating strong atmospheric inflation below millibar pressures. We have since started analyses of high-resolution observations of a number of other, cooler hot Jupiters. During my talk I will announce new, strong detections of neutral and ionised metals in these atmospheres. The discovery of multiple metals in multiple planets at high confidence demonstrates that detailed chemical analyses of ultra-hot Jupiter atmospheres are indeed possible, and that the community can move beyond the notion of metallicity, but instead study the chemistry of individual trace metals. In addition, these spectral lines are powerful tools to constrain atmospheric dynamics and structure.
David Ehrenreich (Geneva) – Detection of Planetary Rotation and a Strong East Wind on an Ultra-hot Gas Giant with ESPRESSO at the VLT
The stellar radial velocity anomaly measured during an exoplanet transit (the Rossiter-McLaughlin effect) allows to constrain the orbital architecture of a transiting planetary system and resolve the surface velocity structure of the transited star. Thanks to the exquisite radial velocity precision of the new ESPRESSO high-resolution spectrograph at the Very Large Telescope, we show that the Rossiter-McLaughlin effect of a highly-irradiated gas giant can also be used to diagnostic the existence of a ultra-hot atmosphere. Removing the stellar signature (known as the Doppler shadow) reveals another Doppler signature moving along with the planet, which we attribute to the planetary atmosphere. Since this absorption signal is obtained through the cross-correlation of the spectra with a stellar mask, the exoplanet must contain atomic iron, the main component of stellar cross-correlation masks. The cross-correlation function of the *planet* appears slightly redshifted at the beginning of the transit and becomes strongly blue-shifted as the East (evening) limb enters the stellar disc, indicating a strong asymmetry in the wind velocity between the two limbs. This is seen consistently at two different epochs of observation. We measure the average full-width at half maximum (FWHM) of the planetary signal and obtain the projected rotational velocity of the planet, which we compare to the expected tidally-locked rotation of the close-in exoplanet. ESPRESSO started science operations at the VLT on September 2018 and this is the first scientific result from the consortium that built the instrument. It reveals ESPRESSO, an ESO instrument open to the Community, as an outstanding characterization machine for exoplanetary atmospheres.Contributing Teams: The ESPRESSO GTO Consortium (Portugal: Universities of Porto and Lisbon; Italy: Observatories of Trieste, Turin, Palermo, and Telescopio Nazionale Galileo; Switzerland: Universities of Geneva and Bern; Spain: Institute of Astrophysics of the Canaries, Center of Astrobiology in Madrid; the European Southern Observatory)
Thomas Beatty (Arizona) – The Global Climates, Clouds, and Dynamics of the Hottest Jupiters
The atmospheres of ultra-hot Jupiters (>3000K) exist in an extreme state of day-night disequilibrium, giving us one of the best opportunities to study the dynamic processes in giant planet atmospheres. By using orbital phase curve observations of these planets we can construct a global map of their thermal emission, and watch their atmospheres change as gas moves from day to night and back again. Besides providing us with a better understanding of hot Jupiter atmospheres, this also allows us to study what would otherwise be observationally inaccessible atmospheric processes. Specifically, we can see the formation of clouds near planetary dusk, their destruction shortly after dawn, and use this to constrain the physics of cloud formation and dissolution in both exoplanets and brown dwarfs. We can also use phase curve observations of extremely hot, cloudless, planets to directly trace the underlying dynamics and mixing in these atmospheres. We will illustrate this using new results from our new HST/WFC3 phase curves of KELT-1b and new dual-band Spitzer phase curves of KELT-9b. For KELT-1b, our spectroscopic phase curves of KELT-1b show — for the first time — the broadband and spectroscopic signatures of the formation and break-up of these nightside clouds. Coupled with previous broadband Spitzer phase curve observations, this gives us new insight into the cloud formation timescales and cloud compositions on hot Jupiters. We will also present new 3.6um and 4.5um Spitzer phase curves of KELT-9b, which, at 4600K, is the hottest giant planet known. Unlike all other hot Jupiters, KELT-9b shows a strongly non-sinosoidal phase curve in both Spitzer bands. Also unlike all other hot Jupiters, the extreme temperature of KELT-9b’s atmosphere means that it is completely cloudless, and we will discuss how the phase curve variation we see is driven by atmospheric dynamics. The high temperature also causes molecular hydrogen to dissociate on the dayside, and by using the strong opacity difference between H and H2 in the two IRAC channels, we can use the hydrogen dissociation / recombination reaction as a direct tracer of the atmospheric gas dynamics.
Melodie Kao (Arizona State) – A Window into Planetary Magnetism with Exo-Aurorae
Planetary magnetic fields influence atmospheric evaporation from space weather, yield insights into planet interiors, and are essential for producing aurorae. The most direct way of measuring magnetic fields on exoplanets is by observing exo-aurorae at radio frequencies. Our discovery of the first radio exo-aurora on the ~12.7 MJ brown dwarf SIMP J01365662+0933473 marks the beginning of an era for directly probing magnetism at planetary masses. Low-frequency radio arrays such as the Owens Valley LWA and the Square Kilometre Array will soon be sensitive to exoplanet aurorae, providing a new means of exoplanet detection and characterization. Now is a critical time to prepare for these upcoming searches by harnessing detailed studies of exo-aurorae on observationally accessible exoplanet analogs, planetary-mass brown dwarfs. I will synthesize the state of the art for searches of brown dwarf exo-aurorae, including our new results from a survey of young, planetary-mass objects and the deepest study to date of an 11-12 MJ brown dwarf. I will discuss implications for and highlight opportunities to probe exoplanet magnetism with the next generation of ground- and space-based radio facilities.
10 AM — Coffee Break
10:30 AM — Disks [Chair: Yamila Miguel]
Catherine Espaillat (Boston U) – Protoplanetary Disks and Their Dynamic Host Stars
Protoplanetary disks play a key role not only in understanding planet formation, but also in unlocking the fundamental physics of transport processes given that these are some of the closest astrophysical accretion disks. The young stars hosting these disks are known to be remarkably variable, but it is not clear how the variable high-energy radiation fields of a young star impact the disk and hence planet formation and accretion processes. In order to gain insight to these dynamic systems, multi-epoch and multi-wavelength datasets are necessary. I present the first near-simultaneous multi-epoch X-ray, ultraviolet, optical, infrared, and radio observations of an accreting, young star. These data reveal the first observational evidence of the star-disk-jet connection. The observations show that an increase in the surface density in the inner disk resulted in more mass loading onto the star and therefore a higher accretion rate onto the star, which led to a higher mass-loss rate in the jet. This suggests a linked origin, presumably the stellar magnetic field, which can both channel material onto the star as well as eject it in collimated jets along twisted field lines. This showcases the possibilities for future progress in time-domain studies and emphasizes the importance of coordinated multiwavelength work of these dynamic young systems.
Diana Powell (UC Santa Cruz) – Large Total Masses and Small Amounts of CO Gas in Protoplanetary Disks
The total mass in protoplanetary disks and the C-to-O ratio of solids and gas are critical initial conditions for understanding the speed of planet formation and planetary composition after formation. Several recent studies show that the standard assumptions for both of these quantities are likely incorrect. I will report on our new set of models that reconcile theory with observations of protoplanetary disks and create a new set of initial conditions for planet formation models. This modeling makes use of recent resolved multiwavelength observations of disks in the millimeter to constrain the aerodynamic properties of dust grains, allowing us to infer total disk mass without an assumed dust opacity or tracer-to-H2 ratio. The 7 disks modeled using this method thus far are close to the limit of gravitational stability at certain radii and raise the possibility that all disks are more massive than has been previously appreciated. This qualitative change to the initial conditions of planet formation has sweeping implications. I will present new, unpublished work that combines the microphysics of cloud formation in planetary atmospheres and our new models of protoplanetary disks to show that the observed depletion of CO in TW Hya is consistent with freeze-out processes and that the variable CO depletion observed in disks can be explained by the processes of freeze-out and particle drift. This work both solves an outstanding problem in observations of protoplanetary disks and robustly constrains the C-to-O ratio in gas and solids available for planet formation.
Christophe Pinte (Monash U) – Kinematic Detection of Embedded Protoplanets
We still do not understand how planets form, or why extra-solar planetary systems are so different from our own solar system. Recent observations of protoplanetary discs have revealed rings and gaps, spirals and asymmetries. These features have been interpreted as signatures of newborn protoplanets, but the exact origin is unknown, and remains poorly constrained by direct observation. In this talk, we show how high spatial and spectral resolution ALMA observations can be used to detect embedded planet in their discs. We report the kinematic detections of Jupiter-mass planets in the discs of HD 163296 and HD 97048. For HD 97048, the planet is located in a gas and dust gap. An embedded planet can explain both the disturbed Keplerian flow of the gas, detected in CO lines, and the gap detected in the dust disc at the same radius. While gaps appear to be a common feature in protoplanetary discs, we present a direct correspondence between a planet and a dust gap, indicating that at least some gaps are the result of planet-disc interactions.
Satoshi Mayama (SOKENDAI) – ALMA Reveals a Misaligned Inner Gas Disk inside the Large Cavity of a Transitional Disk
Pairs of azimuthal intensity decrements at near-symmetric locations have been seen in a number of protoplanetary disks. They are most commonly interpreted as the two shadows cast by a highly misaligned inner disk. Direct evidence of such an inner disk, however, remains largely illusive, except in rare cases. In 2012, a pair of such shadows were discovered in scattered-light observations of the near face-on disk around 2MASS J16042165- 2130284, a transitional object with a cavity 60 au in radius. The star itself is a “dipper,” with quasi-periodic dimming events on its light curve, commonly hypothesized as caused by extinctions by transiting dusty structures in the inner disk. Here, we report the detection of a gas disk inside the cavity using Atacama Large Millimeter/submillimeter Array (ALMA) observations with 0.2 [arcsec] angular resolution. A twisted butterfly pattern is found in the moment 1 map of the CO (3–2) emission line toward the center, which is the key signature of a high misalignment between the inner and outer disks. In addition, the counterparts of the shadows are seen in both dust continuum emission and gas emission maps, consistent with these regions being cooler than their surroundings. Our findings strongly support the hypothesized misaligned inner disk origin of the shadows in the J1604-2130 disk. Finally, the inclination of the inner disk would be close to −45[deg] in contrast with 45[deg]; it is possible that its internal asymmetric structures cause the variations on the light curve of the host star.
Thomas Esposito (UC Berkeley) – Polarizing Planetary Systems: New Debris Disks Resolved on Solar System Scales by GPIES
We will present new top-level results from our unprecedented debris disk survey of 100+ stars in near-IR, polarized scattered light with the high-contrast Gemini Planet Imager. This four-year survey is the first of its kind: a uniform probe of young planetary system environments for small dust on Solar System-like scales with polarimetry and high angular resolution. Among the 26 detected disks we will present, seven are scattered-light discoveries, over a dozen are seen in polarized intensity for the first time, and all are resolved on spatial scales of 0.5–7.0 au. On the population level, we constrain the presence of micron-sized grains at stellar separations of 1–20 au for our nearest observed stars and 20–200 au for the farthest: a prime zone for planet formation and migration. We now know the detailed morphologies of these disks, a handful of which either may be disturbed by interaction with low-mass companions or have had perturbing giant planets directly imaged. In one case, an external stellar companion may have truncated the primary star’s disk. We will also link our data to ALMA observations, showing an empirical relationship between the radial locations of small and large disk grains. Going forward in a broader context, our data yield measurements of the disk-scattered light’s polarization fraction, which will be a key factor in determining grain compositions, sizes, and structures that are only weakly constrained otherwise. Thus, GPIES disk data are pushing the bounds of theory and models to explain observations. In summary, we will use our ESS IV oral presentation to share with the exoplanet community the results of the most information-rich survey of scattered-light debris disks ever conducted, one that will inform the design and drive the science goals of advanced instrumentation and facilities that will see first light in the coming decade.
Virginie Faramaz (NASA JPL) – The Debris Disk of HR 8799: Do we Need an Extra Planet?
HR 8799 is so far the only system where multiple planets have been directly imaged. The planetary system is surrounded by an extremely faint debris disk, which detailed observations are now within reach thanks to the sensitivity and resolution power of ALMA. Prior observations of this disk at low (~3) SNR in Band 6 (1.3 mm) led two different teams to derive two different values for the location of the disk inner edge: one result suggests that an additional planet should be present beyond the outermost planet HR 8799 b to carve this inner edge. The other one finds an inner edge location that is, on the contrary, compatible with HR 8799 b carving this inner edge. We present here new high angular resolution observations of this debris disk in Band 7 with ALMA, the most sensitive that were obtained so far, thanks to which we derive an inner edge consistent with the largest value derived from the modeling of the Band 6 emission, and thus confirm that the inner edge of the debris disk would require an additional planet beyond HR 8799 b to have been carved at this distance.
Quentin Kral (Obs Paris) – The Presence of Gas in Debris Discs: What Does It Imply? [Presented by Alexis Brandeker]
Gas is now discovered ubiquitously around main-sequence stars at a stage (>10Myr) where planets have already formed. This gas is always discovered in systems with planetesimal belts (debris disc stage) and is thought to being released from volatile-rich planetesimals when they collide with each other and create the observed dust. I will present the most recent gas detections and new yet unpublished ALMA data showing new detections for the first time around a G-type star (in addition to recent detections around M and F stars), showing that gas release around main sequence stars is not an A-star phenomenon as once thought. I will show what can be learned from all these new gas detections in the main sequence phase for the planetary system as a whole. The main result so far is that, as we are probing gas released from planetesimals, we have a direct access to the volatile content of these exoplanetesimals, which is fundamental as they are the building blocks of planets and may also deliver volatiles when impacting onto Earth-like planets in these systems. I will show how gas evolution models (Kral et al. 2016, 2017, 2019) can help to constrain the composition of these exoplanetesimals. From the gas models, we also derive the viscosity of these gas discs and show that it may be compatible with values given by the magnetorotational instability (MRI, see Kral & Latter 2016), which may allow to test the MRI under new conditions, in low density environments where non-ideal effects (such as the ambipolar diffusion) may be important. Last but not least, our new model is able to explain the most massive gas discs observed (with CO masses greater than 0.01 earth masses) as being of secondary origin as well (Kral et al. 2019), i.e. with gas released from planetesimals rather than being primordial (i.e. a remnant of the protoplanetary disc gas). This has important consequences concerning planetary formation and the fate of protoplanetary discs that can be studied from these gas observations.
Lunch Break
2:00 PM — Habitability and Biosignatures [Chair: Vikki Meadows]
Phil Muirhead (Boston U) – Are Exoplanets Orbiting M Dwarfs Extreme?
M dwarf stars have long spin-down timescales, long activity lifetimes and persistent magnetic activity, all of which have implications for the potential habitability of orbiting planets. I will present results from several research programs investigating M dwarf rotation, activity and evolution. I will discuss a new technique to measure chemical-kinematic ages of main-sequence M dwarf stars. We applied that technique to a variety of nearby M dwarfs, both planet hosts and non-planet hosts, and rapid (young) and slow (old) rotators. We find that relatively slow rotators (P~100 days) do not appear to be alpha enriched, indicating that they are not over 10 Gyrs old. Second, for the rapid rotators, we see clear evidence of Zeeman enhancement of Y-band Ti I lines as a function of Rossby number. While other activity indicators, such as H-alpha and X-ray emission, appear to saturate with low Rossby number, Zeeman enhancement does not, indicating that the saturation mechanism is confined to the chromosphere and corona. Finally, I will present new results on the M dwarf radius problem. Using spectral synthesis methods, we find that large magnetic star spot fractions are primarily responsible for observed discrepancies between model and measured stellar radii in fully convective M dwarf stars. As most M dwarfs appear discrepant, our results suggest the vast majority of M dwarfs have large spot fractions and correspondingly high localization of magnetic fields.
Amber Medina (Harvard) – Flare Statistics and High Resolution Spectroscopy of a Volume Complete Sample of Mid-to-Late M dwarfs within 15 Parsecs
Main-sequence stars with masses less than 30% that of the Sun are fully convective and are the most abundant stars in the galaxy. The question of how fully convective stars generate their magnetic field is of intrinsic interest and also bears upon the habitability of their orbiting planets. These stars currently provide the best opportunities to study planets in the habitable zone, so it is essential we characterize their magnetic activity. We are currently undertaking a multi-epoch high-resolution spectroscopic survey in addition to obtaining (through a TESS GI program) two-minute cadence data of a volume-complete sample of stars with masses between 0.1-0.3 the solar value and within 15 parsecs. The stars in the sample are well-characterized with accurate masses and radii, and photometric rotation periods from the MEarth project. We determined the statistics of flares on all mid-to-late M dwarfs within 15 parsecs observed by TESS to-date. We use our complementary high-resolution spectroscopic measurements of rotational velocities, H-alpha equivalent widths, along with our galactic space motions (calculated from our measured radial velocities) to correlate the ages and activity levels of this population to the flare rates, luminosities, and durations. This work is supported by grants from the John Templeton Foundation, the David and Lucile Packard Foundation, and the US National Science Foundation.
Matthew Hoskin (Warwick) – Volatile- and Water-rich Planetary Material Accreting onto a White Dwarf
We report the discovery of a white dwarf that has an unusually large amount of hydrogen, ~5% by mass, within its helium atmosphere. Such a mixture cannot result from the past evolution of this star alone (Rolland+, 2018). The only plausible explanation is that this white dwarf has recently accreted ~1022g of water – as much as 1% of the Earth’s oceans. Absorption lines of the major mineral-forming elements (O, Mg, Si, Ca, Fe, Ni) and of volatile elements (C, S, P) detected in our VLT and Hubble Space Telescope spectroscopy unambiguously demonstrate that the star is currently accreting planetary debris. Our abundance analysis indicates a comet-like nature of the disrupted planetesimal, carrying the material necessary for seeding terrestrial exo-planets with the building-blocks of life. Small traces of hydrogen are common in helium atmosphere white dwarfs, and are often found alongside pollution by planetary debris, providing clear statistical evidence that water-rich rocky bodies prevale into the final stages of stellar and planetary evolution (Gentile Fusillo+, 2017). This connection is corroborated by this spectacularly polluted white dwarf, which has accreted a sufficient amount of water to change its past and future spectra evolution.
Howard Chen (Northwestern) – M-dwarf Activity Driven 3D Climate and Photochemistry of Inner Habitable Zone Tidally-Locked Planets
Planets residing in circumstellar habitable zones (CHZs) offer our best opportunities to test hypotheses of life’s potential pervasiveness and complexity. Constraining the precise boundaries of habitability and its observational discriminants is thus critical to maximizing our chances at remote life detection for future instruments. Conventionally, calculations of the inner edge of the habitable zone (IHZ) have been performed using both 1D climate models and 3D general circulation models. However, these models lack interactive three-dimensional chemistry and do not resolve the observationally-critical mesosphere and lower thermosphere (MLT). Here we employ a 3D chemistry-climate model (CCM) to simulate the atmospheres of synchronously- rotating planets orbiting at the inner edge of habitable zones of K- and M-dwarf stars (between Teff = 4000 K and 2600 K) with N2-O2-H2O-CO2 atmospheres. With the inclusion of interactive chemistry, we find that simulated runaway and moist greenhouse thresholds are in good agreement with previous GCM studies. However, around quiescent stars, our prognostic hydrogen mixing ratios are orders of magnitude lower than previous diagnostic estimates, suggesting that planets in these systems are less vulnerable to desiccation via water escape. Additionally, we find that around active M-dwarfs, increases in upper atmospheric moisture and photodissociation rates allow hydrogen mixing ratios to approach that of water vapor, leading to elevated water loss efficiency via diffusion-limited escape. Using our CCM results as inputs, translated transmission and emission spectra show that both water vapor and ozone features could be detectable by future missions such as the James Webb Space Telescope.
Lisa Kaltenegger (Cornell) – Dark Water Oceans on Exoplanets Orbiting Cool Stars
Several thousand extrasolar planets orbiting other stars provide a first glimpse into the diversity of other worlds. We show that oceans on worlds orbiting different alien Suns will differ from Earth’s oceans because the penetration depth of light can be very different, altering ocean dynamics significantly. While Sunlight can penetrate up to 250m in a water ocean, light may penetrate as little as 2m for oceans illuminated by cool red stars. Dynamics and photosynthesis in water oceans on exoplanets and exomoons orbiting other Suns can be very different from Earth’s. We introduce a new paradigm for the hydrosphere-atmosphere interaction in planetary models. The idea is fundamental – when you convolute the absorption of water with wavelength with the irradiation exoplanets receive from different host stars it fundamentally changes how deep that light can penetrate water, especially for cool host star planets like the detected, potentially habitable planets around our neighboring stars Proxima-b and the planets in the Trappist-1 system. Our paper shows the huge impact the host star irradiation has on the thermal structure and resulting dynamics on water oceans on extrasolar planets. Additionally, the depth below which there is generally insufficient light for photoactive organisms in oceans on a red star will be much shallower than on Earth. Thus, photosynthetic ocean life, if it exists, will be much closer to the ocean surface, and can be more readily detected on planets and moons orbiting red stars.
Dimitar Sasselov (Harvard) – Prebiotic Planets: Evaluating Planetary Conditions for Origins of Life
We often discuss exoplanet habitability, but rarely focus on the prebiotic planets – the ones with geochemical conditions conducive to the emergence of life. How could prebiotic exoplanets, if we could identify them, help us solve life’s origins? In this talk I will focus on the prebiotic synthesis of the nucleotides, amino acids and lipids needed for life as we know it and the planetary environmental context that makes that synthesis possible. I will argue that, as we still struggle to understand life’s origins on Earth, there are general predictions about the global planetary conditions that are testable with upcoming spectroscopic observations of the atmospheres of rocky exoplanets.
3:30 PM – Coffee Break
4:00 PM — Future Missions [Chair: Tiffany Kataria]
Evgenya Shkolnik (Arizona State) – Expanding our Telescope Toolkit: Exoplanet Science Opportunities with SmallSats
New technologies can disrupt the status quo by challenging the current assumptions and opening up new avenues of research. Small satellites, including CubeSats, have been growing in popularity in many science and technology fields, yet are only now beginning to receive attention as tools for astrophysics research. When deployed as space-based telescopes, SmallSats enable science experiments not possible with existing or planned large space missions. We trade some capabilities such as mirror size for lower cost and shorter build times for more frequent launch opportunities, with two additional and crucial advantages over large, over-subscribed telescopes: SmallSats can monitor sources for weeks or months at time, and at wavelengths not accessible from the ground such as the ultraviolet, far-infrared and low-frequency radio. Achieving high-impact astronomical research with SmallSats is becoming increasingly feasible with advances in technologies such as precision pointing and compact sensitive detectors. SmallSats may also pair well with the large space- and ground-based telescopes providing complementary data to better explain the physical processes observed. There are many possible exoplanet-focused science cases for SmallSats, several of which are already in development and more ideas yet to be proposed. I will share our experiences developing the NASA-funded SPARCS (Star-Planet Activity Research CubeSat) mission as a case study to explore the challenges and opportunities of astrophysics SmallSats.
Christopher Broeg (U Bern) – The CHEOPS Mission: Launch Imminent for ESA’s Next Exoplanet Mission
The CHaracterising ExOPlanet Satellite (CHEOPS) is a mission jointly led by Switzerland and ESA which was selected in October 2012 as the first S-class mission in the ESA Science Programme. CHEOPS will be the first space observatory dedicated to search for transits of exoplanets by means of ultrahigh precision photometry on bright stars already known to host planets. It will have access to more than 2/3 of the sky and provide the unique capability of determining accurate radii for planets of known mass from ground-based spectroscopic surveys. This will allow a first order characterisation of the planets’ internal structure by determination of their mean density, which provides direct insights into their composition. CHEOPS will also provide precise radii for new planets discovered by the next generation of ground- or space-based transits surveys. To reach its goals, CHEOPS is designed to measure photometric signals with a precision of 20 ppm in 6 hours integration time on magnitude 9 stars, and 85 ppm in 3 hour integrations on magnitude 12 stars. The CHEOPS payload is a single telescope of 30 cm clear aperture, which has a single CCD focal plane detector. In Ritchey-Chrétien telescope optical configuration it provides a defocussed image of the target star. The main design drivers are related to the compactness of the optical system and to the capability to reject the stray light. The nominal CHEOPS operational orbit is a polar Sun-Synchronous Orbit (SSO) with an altitude of 700 km and a local time of the ascending node (LTAN) of 6 am; the orbit inclination is about 98° and the orbital period is 100 min. The nominal mission lifetime is 3.5 years, with a possible extension to 5 years. CHEOPS will launch as auxillary passenger on a Soyuz from Kourou. The launch is imminent with the launch window defined by Arianespace from 15 October to 14 November this year. This talk will review the CHEOPS mission, its scientific goals and mission design. We will discuss the expected performances and also present latest analysis of the ground calibration campaign. An overview of the GTO programme will be presented./p>
Andy Skemer (UC Santa Cruz) – Exoplanet Imaging with ELTs and the TMT’s Planetary Systems Imager
The combination of high angular resolution and sensitivity will allow ELTs to image hundreds of exoplanets ranging from gas-giants to super-earths and even a handful of rocky planets. I will review the different types of exoplanets that will be observable with ELTs and also discuss how spectroscopy will enable measurements of molecular abundances, T-P profiles, cloud properties, spin rates, accretion, and weather. Finally I will present an overview of the Planetary Systems Imager, the TMT’s multi-wavelength exoplanet imaging platform.
Göran Pilbratt (ESA/ESTEC) – ARIEL: ESA’s Mission to Study the Nature of Exoplanets
The ~4000 exoplanets currently known display a great diversity of physical parameters, and orbit stars with different properties and planetary system architectures. For most of them we know only either mass or size, or both. However, planetary modelling based on sizes and masses alone suffer from important degeneracies. To independently measure chemical composition is the next challenge. It would enable improved modelling, which will enhance our understanding of what planets are made of, how planets and planetary systems form, and how planets and their atmospheres evolve to what we observe today. The Atmospheric Remote-Sensing Infrared Exoplanet Large-survey (ARIEL) mission has been selected by ESA as M4 in the Cosmic Vision programme for a 2028 launch. ARIEL is dedicated to performing measurements of the chemical composition and dynamics of exoplanet atmospheres for a large population (many hundreds) of known diverse preferentially warm and hot transiting planets, enabling the understanding of the physics and chemistry of these far away worlds. The observations will probe atmospheric chemistry and dynamics, by means of infrared spectroscopy in three bands (covering 1.1-7.8 um) and visible/NIR photometry in three bands (covering 0.5-1.1 um). All six bands are observed simultaneously with an off-axis Cassegrain telescope having a ~1.1 x 0.7 m aperture. Both transit and eclipse/occultation spectroscopy will be employed to obtain transmission and emission spectra. The photometry provides thermal and scattering properties and monitors stellar activity. ARIEL will conduct its observations from a large halo orbit around the Sun-Earth L2 point. ARIEL wants to embrace the general community, by offering open involvement in target selection, and by providing timely public releases of high quality data products at various processing levels throughout the mission. In this presentation I will provide an overview of all aspects of the mission, describe the current ongoing activities in ESA, the ARIEL Consortium, and industry, and the overall schedule.
Eliza Kempton (U Maryland) – Using JWST to Determine Whether M Dwarf Terrestrial Planets Possess Atmospheres
In the era of TESS, we expect to detect legions of planets for which atmospheric characterization will be possible with JWST. Perhaps the most exciting among these planets are the rocky ones, which up until now have not been accessible to atmospheric studies. Yet small rocky planets will still be challenging targets for JWST, so the question arises of how best to use JWST to make tangible progress toward understanding the atmospheres of terrestrial bodies. We posit that JWST is best suited to distinguish between rocky planets that do and do not possess atmospheres by photometrically observing their secondary eclipses. The argument is as follows. The dayside temperature of a tidally locked planet will be reduced by the presence of an atmosphere, either because the atmosphere transports heat to the night side of the planet or because atmospheric scatterers such as clouds will increase the planet’s Bond albedo. There is therefore a maximal secondary eclipse depth that is representative of a hot dayside hemisphere with no atmosphere present. We focus on planets orbiting M stars because they are being discovered in large numbers by current facilities, they are within the observational grasp of JWST, and there is considerable skepticism as to whether these planets can retain atmospheres at all given the high-energy irradiation from their host stars. I will present the results from a multi-institution collaboration investigating the promise and the limits of secondary eclipse photometry as a test for candidate atmospheres on rocky M-dwarf planets. We have developed a suite of general circulation models and radiative-convective atmospheric structure models, and have developed our understanding of rocky planet surface geochemistry, in order to address this topic. We have focused our efforts on three warm transiting super-Earths that will be ideal targets for secondary eclipse investigations with JWST. We find that JWST can distinguish between planets with and without atmospheres in as little as a one eclipse — a time investment that significantly outperforms phase curves and the more traditional transit spectroscopy techniques.
Matthew Penny (Ohio State) – Exploring Exoplanet Demographics Beyond 1 AU with the WFIRST Microlensing Survey
As outlined by the 2010 Decadal Survey, NASA’s next flagship mission WFIRST will conduct wide-field infrared surveys and demonstrate space-based coronagraphy techniques necessary to directly image exoplanets in reflected visible light. We will give an update on the status of the WFIRST mission, focusing on its two major exoplanet goals. Using its wide field instrument (WFI), WFIRST will carry out a large exoplanet microlensing survey toward the Galactic bulge. This survey is designed to statistically explore exoplanet demographics over a wide range of orbital separations (from <~1 AU to infinity [i.e., free-floating planets]), and five orders of magnitude in mass (super-Jupiters down to a few lunar masses). These broad statistics will provide vital, and otherwise unobtainable, observational constraints on the end products of the planet formation process, and on the occurrence rates of low-mass planets in wider orbits than can be probed by radial velocity and transit techniques. Focusing on recent and upcoming results from the WFIRST Microlensing Science Investigation Team, we will describe new estimates of WFIRST’s capabilities to detect bound and free-floating planets, the development of techniques required to measure microlensing planet masses, and the results of a data challenge designed to test planet detection and modelling techniques on WFIRST-like simulated data. For the coronagraph instrument (CGI) we present a few key highlights of CGI’s predicted capabilities for characterizing nearby planetary systems via its technology demonstration of extreme contrast coronagraphic imaging and spectroscopy in visible light. CGI will demonstrate five main areas that aid future direct imaging missions such as LUVOIR and HabEX: exquisite wavefront control through a pair of deformable mirrors, suppression of an on-axis star’s diffraction pattern through occulting masks or shaped pupils, the use of photon counting visible detectors, and post-processing techniques at high contrast in space, and high contrast spectroscopy.
Jennifer Burt (MIT) – Radial Velocity Science in the 2020s: The Future of Ground-based EPRV Surveys
The radial velocity community has delivered a variety of new and exciting instruments around the globe over the past two years. While many of these facilities began operations during the end of the 2010s, their true science impact will not be felt until the 2020s. Extreme precision radial velocity instruments such as ESPRESSO, EXPRES, and Neid will allow for detailed monitoring of our closest stellar neighbors on a scale that has never been seen before. They will obtain mass measurements for many of the smallest transiting planets from missions like TESS, in addition to surveying nearby stars in search of the short period, terrestrial planets that we expect based on the Kepler planet occurrence rates. Meanwhile, near-infrared spectrographs like HPF, SPIRou, and IRD will facilitate searches for planets around the coolest nearby stars, targeting a variety of stellar host that has not previously been surveyed by Doppler facilities. I will discuss the upcoming advancements within these branches of radial velocity science and how they are expected to expand the current boundaries of exoplanet discovery space.