PROJECT EOS March 15, 2020

EARTHS IN OTHER SOLAR SYSTEMS

Recent Publications

ACCESS: A Visual toNear-infrared Spectrum of the Hot Jupiter WASP-43b with Evidence of H2O, but No Evidence of Na or K ………………………………. Identifying Exo-Earth Candidates in Direct Imaging Data through PROJECT EOS Bayesian Classification ………………………………. Nautilus: A Very Large-Aperture, Ultralight Space Telescope for Exoplanet Exploration, Time- domain Astrophysics, and Faint Objects ………………………………. EPOS: Exoplanet Population Earths in Other Solar Systems is part of NASA’s Nexus for Observation Simulator Exoplanetary System Science program, which carries out ……………………………….. coordinated research toward to the goal of searching for and ACCESS: the Arizona-CfA- determining the frequency of habitable extrasolar planets with Catolica-Carnegie Exoplanet atmospheric biosignatures in the Solar neighborhood. Spectroscopy Survey Our interdisciplinary EOS team includes astrophysicists, ……………………………….. Exoplanet Population Synthesis in planetary scientists, cosmochemists, material scientists, the Era of Large Exoplanets chemists and physicists. Surveys The Principal Investigator of EOS is Daniel Apai (University of ……………………………….. Arizona). The project’s lead institutions are The University of The Sun-like Stars Opportunity ……………………………….. Arizona‘s Steward Observatory and Lunar and Planetary Life Beyond the Solar System: Laboratory. Remotely Detectable The EOS Institutional Consortium consists of the Steward Biosignatures Observatory and the Lunar and Planetary Laboratory of the ……………………………….. Planet formation and migration University of Arizona, the National Optical Astronomy near the silicate sublimation front Observatory, the Department of Geophysical Sciences at the in protoplanetary disks University of Chicago, the Planetary Science Institute, and the ……………………………….. Catholic University of Chile. Search for L5 Earth Trojans with For a complete list of publications, please visit the DECam EOS Library on the SAO/NASA Astrophysics Data System. eos-nexus.org 1 PROJECT EOS March 15, 2020

EARTHS IN OTHER SOLAR SYSTEMS

Recent Publications (cont.)

Characterization and Properties of Earth-like Origins Seminar Planets ………………………………. The Origins Seminar series brings together ISM, star Cloud Atlas: High-precision and planet formation people, exoplanets experts, HST/WFC3/IR Time-Resolved planetary scientists and astrobiologists. Topics range Observations of Directly- from molecular clouds through star and planet Imaged Exoplanet formation to exoplanets detection and HD106906b characterization and astrobiology. ………………………………. The ACCESS Exoplanet The seminar series is organized by Serena Kim (SO), Transmission Spectroscopy Sebastiaan Krijt (SO) and Kamber Schwarz (LPL) from Survey Steward Observatory/Dept. of Astronomy and Dept. ………………………………. of Planetary Sciences (LPL) at the University of Arizona. Nautilus: A Biosignature The Origins Seminar series is partly supported by the Survey in a Thousand Exo- Earths in Other Solar Systems NExSS team. Earths During the summer, talks take place 11:00am – ……………………………….. 12:00pm (PT) on Mondays. To receive weekly updates The role of planetesimals and advertisements for talks, please subscribe to the and gas in the orbital mailing list. If you are interested in presenting your assembly of work during one of the open slots, feel free to contact close-in exoplanets the organizers. ……………………………….. During the Spring and Summer 2020 the Origins Hints on the origins of seminar meets via zoom due to the Covid-19 particle traps in Pandemic. We may continue to meet via zoom in the protoplanetary disks given Fall 2020, depending on the status of the Pandemic by the Mdust−M⋆ relation and guidelines by the department and the University. ……………………………….. The zoom information is sent via email. The evolution of dust-disk sizes from a homogeneous analysis of 1-10 Myr-old stars

eos-nexus.org 2 PROJECT EOS March 15, 2020

ACCESS: A Visual to Near-infrared Spectrum of the Hot Jupiter

WASP-43b with Evidence of H2O, but No Evidence of Na or K

Weaver, Ian C.; López-Morales, Mercedes; Espinoza Néstor; Rackham, Benjamin V.; Osip, David J.; Apai, Dániel; Jordán Andrés; Bixel, Alex; Lewis, Nikole K.; Alam Munazza K.; Kirk, James; McGruder, Chima; Rodler Florian; Fienco, Jennifer

The Astronomical Journal, Vol. 159, Number 1

We present a new ground-based visual transmission spectrum of the hot Jupiter WASP-43b, obtained as part of the ACCESS Survey. The spectrum was derived from four transits observed between 2015 and 2018, with combined wavelength coverage between 5300 and 9000 Å and an average photometric precision of 708 ppm in 230 Å bins. We perform an atmospheric retrieval of our transmission spectrum combined with literature Hubble Space Telescope/WFC3 observations to search for the presence of clouds/hazes as well as Na, K, Hα, and H2O planetary absorption and stellar spot contamination over a combined spectral range of 5318–16420 Å. We do not detect a statistically significant presence of Na I or K I alkali lines, or Hα in the atmosphere of WASP-43b. We find that the observed transmission spectrum can be best explained by a combination of heterogeneities on the photosphere of the host star and a clear planetary atmosphere with H2O. This model yields a log evidence of 8.26 ± 0.42 higher than a flat (featureless) spectrum. In particular, the observations marginally favor the presence of large, low- contrast spots over the four ACCESS transit epochs with an average covering fraction and temperature contrast ΔT = 132 K ± 132 K. Within the planet's atmosphere, we recover a log H2O volume mixing ratio of which is consistent with previous H2O abundance determinations for this planet.

Figure 1: Raw integrated white-light-curve flux of WASP-43 (gray) and comparison stars (color) observed with IMACS, centered 1 hr around the predicted midtransit time. We calculated the predicted midtransit times with Swarthmore College’s online transit finding tool (https://astro.swarthmore.edu/transits.cgi). eos-nexus.org 3 PROJECT EOS March 15, 2020

Identifying Exo-Earth Candidates in Direct Imaging Data through Bayesian Classification

Bixel, Alex; Apai, Dániel

The Astronomical Journal, Vol. 159, Number 1

Future space telescopes may be able to directly image between approximately 10 and 100 planets with sizes and orbits consistent with habitable surface conditions ("exo-Earth candidates" or EECs), but observers will face difficulty in distinguishing these from the potentially hundreds of nonhabitable "false positives" which will also be detected. To maximize the efficiency of follow-up observations, a prioritization scheme must be developed to determine which planets are most likely to be EECs. In this paper, we present a Bayesian method for estimating the likelihood that any directly imaged extrasolar planet is a true EEC by interpreting the planet's apparent magnitude and separation in the context of existing exoplanet statistics. As a specific application of this general framework, we use published estimates of the discovery yield of future space- based direct-imaging mission concepts to conduct "mock surveys" in which we compute the likelihood that each detected planet is an EEC. We find that it will be difficult to determine which planets are EECs with >50% confidence using single-band photometry immediately upon their detection. The best way to reduce this ambiguity would be to constrain the orbit of a given planet by revisiting the system multiple times or through a radial velocity precursor survey. Astrometric or radial velocity constraints on the mass of the planet would offer a lesser benefit. Finally, we show that a Bayesian approach to prioritizing targets would improve the follow-up efficiency of a direct imaging survey versus a blind approach using the same data. For example, the prioritized approach could reduce the amount of integration time required for the spectral detection (or rejection) of water absorption in most EECs by a factor of two.

Figure 1: To illustrate the degeneracies which affect the interpretation of direct imaging data, we simulate the detection of a planet orbiting a Solar-type star at 15 pc (center panel), as well as several planets of varying sizes, orbits, and albedos which have a similar projected separation and magnitude (surrounding panels). It is not clear whether this data point represents a true EEC, or one of many potential false positives. The color and size of each circle represents the potential radius of the planet; only green points are approximately Earth-sized (∼0.8–1.6 R⊕). The color of the potential orbit represents its insolation; only green orbits are in the habitable zone. An “x” marks the planet’s closest approach to the observer. eos-nexus.org 4 PROJECT EOS March 15, 2020

Nautilus: A Very Large-Aperture, Ultralight Space Telescope for Exoplanet Exploration, Time-domain Astrophysics, and Faint Objects

Apai, Dániel; Bixel, Alex; Rackham, Benjamin V.; Schneider, Glenn; Milster, Tom D.; Kim, Dae Wook; Liang, Ronguang; Arenberg, Jonathan; Grunsfeld, John

Astro2020: Decadal Survey on Astronomy and Astrophysics, APC white papers, no. 141

Nautilus is a Probe-class mission concept that will explore the diversity of rocky exoplanets through transit spectroscopy, characterize habitable planets, and search for biosignatures in nearby transiting planets. By providing a larger collecting area than HST and JWST combined, Nautilus will obtain low-resolution spectra simultaneously in the visual (0.5–1 m) and near-infrared (1– 1.7 m). It will observe >1,000 transits of 500 small (Earth- to Neptune-sized) planets discovered by TESS, PLATO, and other surveys. Nautilus will provide the largest and most sensitive library of atmospheric abundances of small exoplanets for decades. With an image quality on par with HST but with 12–15 greater sensitivity – due to its larger collecting area and simpler, higher efficiency instrument – Nautilus will also revolutionize time-domain astrophysics and studies of faint astrophysical sources.

Nautilus achieves its uniquely high sensitivity by utilizing an 8.5m diameter, ultralight, achromatic, multi-order diffractive lens instead of a traditional primary mirror. The Nautilus architecture is simple and designed for robustness and low cost-to-collecting-area ratio. The Nautilus mission concept is expected to greatly reduce fabrication and launch costs, and mission risks compared to the current space telescope paradigm. This paradigm shift will also enable incoherent telescope arrays with collecting area equivalent to that of a 50m telescope [1], but at a very low cost and with a scalable design that distributes risks between many units.

Figure 1: Comparison of the apertures of current (HST) and future (JWST, ARIEL) space telescopes capable of exoplanet transmission spectroscopy to that of Nautilus.

eos-nexus.org 5 PROJECT EOS March 15, 2020

EPOS: Exoplanet Population Observation Simulator Mulders, Gijs D.; Pascucci, Ilaria; Apai, Dániel; Ciesla, Fred J.

The Astronomical Journal, Vol. 156, Number 1

The Kepler survey provides a statistical census of planetary systems out to the habitable zone. Because most planets are non-transiting, orbital architectures are best estimated using simulated observations of ensemble populations. Here, we introduce EPOS, the Exoplanet Population Observation Simulator, to estimate the prevalence and orbital architectures of multi-planet systems based on the latest Kepler data release, DR25. We estimate that at least 42% of Sun-like stars have nearly coplanar planetary systems with seven or more exoplanets. The fraction of stars with at least one planet within 1 au could be as high as 100% depending on assumptions about the distribution of single transiting planets. We estimate an occurrence rate of planets in the habitable zone around Sun-like stars of η ⊕ = 36 ± 14%. The innermost planets in multi-planet systems are clustered around an orbital period of 10 days (0.1 au), reminiscent of the protoplanetary disk inner edge, or which could be explained by a planet trap at that location. Only a small fraction of planetary systems have the innermost planet at long orbital periods, with fewer than ≈8% and ≈3% having no planet interior to the orbit of Mercury and Venus, respectively. These results reinforce the view that the solar system is not a typical planetary system, but an outlier among the distribution of known exoplanetary systems. We predict that at least half of the habitable zone exoplanets are accompanied by (non-transiting) planets at shorter orbital periods, hence knowledge of a close-in exoplanet could be used as a way to optimize the search for Earth-size planets in the Habitable Zone with future direct imaging missions.

Figure 8: Orbital period distribution of the innermost planet in each system. The intrinsic distribution is shown with the red line while the solid blue histograms show the distribution of detections in the simulated survey. The observable distribution is skewed toward shorter orbital periods by detection biases.

eos-nexus.org 6 PROJECT EOS March 15, 2020

ACCESS: the Arizona-CfA-Catolica-Carnegie Exoplanet Spectroscopy Survey McGruder, Chima; Lopez-Morales, Mercedes; Apai, Dániel; Jordán, Andrés; Osip, David; Bixel, Alex; Espinoza, Néstor; Fortney, Jonathan; Kirk, James; Lewis, Nikole; Rackham, Benjamin; Rodler, Florian; Weaver, Ian

American Astronomical Society, Extreme Solar Systems 4, id. 326.22

Transmission spectroscopy provides a powerful tool to study the atmospheric properties of exoplanets. Optical transmission spectra are particularly important, since they provide the spectral baselines for clear, cloudy, and hazy atmospheres needed to correctly interpret infrared transmission spectra observed with HST and the upcoming JWST. For 6 years the Arizona-CfA-Católica-Carnegie Exoplanet Spectroscopy Survey (ACCESS) has been observing and analyzing the atmospheres of over a dozen planets, ranging from hot Jupiters to super-Earths. These observations have been collected with IMACS mounted on the 6.5-m Magellan telescope with a homogeneous setup designed for measurements from 0.4-0.9 microns. The homogeneity of ACCESS's data is extremely important because it allows for minimization of systematic differences between instruments and better optimization of data analysis techniques. This dataset has allowed us to study 1) how stellar heterogeneities can masquerade as atmospheric features and some methods to correct for such effects, 2) optimal detrending algorithms that produce the highest accuracy and precision, 3) observing techniques with ACCESS's telescopes that produce the greatest scientific yield, and more. We give an overview of the status of the survey and summarize the main findings from our published studies. We also describe the expansion of ACCESS to the northern hemisphere with the new BINOSPEC spectrograph on the 6.5-m MMT and our plans to start characterizing the atmospheres of transiting planets discovered by TESS.

eos-nexus.org 7 PROJECT EOS March 15, 2020

Exoplanet Population Synthesis in the Era of Large Exoplanets Surveys Mulders, Gijs Dirk; Mordasini, Christoph; Pascucci, Ilaria; Ciesla, Fred; Emsenhuber, Alexandre; Apai, Dániel

American Astronomical Society, Extreme Solar Systems 4, id. 309.09

The Bern planet population synthesis models (e.g. Mordasini 2018) represent a decade long effort to investigate the integrated effects of the processes at work during planet formation and make predictions for exoplanet populations, planetary system architectures, and planet compositions. Over the last few years new physical mechanisms have been incorporated and adjusted to reflect the lessons learned from Kepler, in particular on atmospheric loss shaping the planet radius distribution and N-body interactions setting the architectures of planetary systems. By comparing the synthetic planet populations to observed exoplanet systems we can constrain planet formation mechanisms to inform predictions of planetary compositions.

This poster shows simulated planet populations from the latest version of the Bern planet population synthesis model. I will make detailed, quantitative comparisons between what the synthetic population would look like compared to exoplanet survey data using the Exoplanet Population Observation Simulator (EPOS), which takes into account the unique observation biases in both transit and radial velocity surveys. While the synthetic populations reproduce many key features seen in the known populations of radial velocity giant planets and systems of close-in super-earths observed with Kepler, we also see key differences in other diagnostics. These differences inform the setup for the Next Generation of Planet Population Synthesis (NGPPS) models.

eos-nexus.org 8 PROJECT EOS March 15, 2020

The Sun-like Stars Opportunity

Arney, Giada; Batalha, Natasha; Britt, Amber V.; Cowan, Nicolas; Domagal-Goldman, Shawn D.; Dressing, Courtney; France, Kevin; Fujii, Yuka; Kopparapu, Ravi; Kane, Stephen; Krissansen-Totton, Joshua; Lincowski, Andrew; Lehmer, Owen; Lopez, Eric; Lustig-Yaeger, Jacob; Meadows, Victoria S.; Olson, Stephanie; Paranteau, M. Niki; Pascucci, Ilaria; Ramirez, Ramses; Reinhard, Christopher; Roberge, Aki; Robinson, Tyler D.; Schwieterman, Edward; Stark, Christoper; Wolf, Eric. T.; Youngblood, Allison

Astro2020: Decadal Survey on Astronomy and Astrophysics, science white papers, no. 91

Observations of exoplanets around Sun-like (i.e. FGK) stars will allow us to place our planet into a larger cosmic context and may offer the best chance of finding habitable, and inhabited, planets. New facilities beyond those currently planned would be required to accomplish these observations. Exoplanet community reports have emphasized the importance of observations of exoplanets in the habitable zones of Sun-like stars for over a decade. This trend continued in the recent Exoplanet Science Strategy report. We endorse the findings and recommendations published in the National Academy reports on Exoplanet Science Strategy and Astrobiology Strategy for the Search for Life in the Universe. This white paper extends and complements the material presented therein.

Figure 1: The recommended exoplanet science strategy from the 2008 Report of the ExoPlanet Task Force. Track 1 (M dwarfs) is now in progress. Track 2 (F, G, K dwarfs; i.e. “Sun-like” stars) will require major new technology and facilities for significant progress. Figure credit: Figure 1 from the Report of the ExoPlanet Task Force (Lunine et al., 2008).

eos-nexus.org 9 PROJECT EOS March 15, 2020

Life Beyond the Solar System: Remotely Detectable Biosignatures

Shawn Domagal-Goldman, Nancy Y. Kiang, Niki Parenteau, David C. Catling, Shiladitya DasSarma, Yuka Fujii, Chester E. Harman, Adrian Lenardic, Enric Pallé, Christopher T. Reinhard, Edward W. Schwieterman, Jean Schneider, Harrison B. Smith, Motohide Tamura, Daniel Angerhausen, Giada Arney, Vladimir S. Airapetian, Natalie M.Batalha, Charles S. Cockell, Leroy Cronin, Russell Deitrick, Anthony Del Genio, Theresa Fisher, Dawn M. Gelino, J. Lee Grenfell, Hilairy E. Hartnett, Siddharth Hegde, Yasunori Hori, Betül Kaçar, Joshua Krissansen-Totten, Timothy Lyons, William B. Moore, Norio Narita, Stephanie L. Olson, Heike Rauer, Tyler D. Robinson, Sarah Rugheimer, Nick Siegler, Evgenya L. Shkolnik, Karl R. Stapelfeldt, Sara Walker

Astro2020: Decadal Survey on Astronomy and Astrophysics, science white papers, no. 528

For the first time in human history, we will soon be able to apply the scientific method to the question "Are We Alone?" The rapid advance of exoplanet discovery, planetary systems science, and telescope technology will soon allow scientists to search for life beyond our Solar System through direct observation of extrasolar planets. This endeavor will occur alongside searches for habitable environments and signs of life within our Solar System. While the searches are thematically related and will inform each other, they will require separate observational techniques. The search for life on exoplanets holds potential through the great diversity of worlds to be explored beyond our Solar System. However, there are also unique challenges related to the relatively limited data this search will obtain on any individual world. This white paper reviews the scientific community's ability to use data from future telescopes to search for life on exoplanets. This material summarizes products from the Exoplanet Biosignatures Workshop Without Walls (EBWWW). The EBWWW was constituted by a series of online and in person activities, with participation from the international exoplanet and astrobiology communities, to assess state of the science and future research needs for the remote detection of life on planets outside our Solar System.

eos-nexus.org 10 PROJECT EOS March 15, 2020

Planet formation and migration near the silicate sublimation front in protoplanetary disks Flock, Mario; Turner, Neal J.; Mulders, Gijs D.; Hasegawa, Yasuhiro, Nelson, Richard P.; Bitsch, Bertram

Astronomy & Astrophysics, Volume 630

Context. The increasing number of newly detected exoplanets at short orbital periods raises questions about their formation and migration histories. Planet formation and migration depend heavily on the structure and dynamics of protoplanetary disks. A particular puzzle that requires explanation arises from one of the key results of the Kepler mission, namely the increase in the planetary occurrence rate with orbital period up to 10 days for F, G, K and M stars. Aims: We investigate the conditions for planet formation and migration near the dust sublimation front in protostellar disks around young Sun-like stars. We are especially interested in determining the positions where the drift of pebbles would be stopped, and where the migration of Earth-like planets and super- Earths would be halted. Methods: For this analysis we use iterative 2D radiation hydrostatic disk models which include irradiation by the star, and dust sublimation and deposition depending on the local temperature and vapor pressure. Results: Our results show the temperature and density structure of a gas and dust disk around a young Sun-like star. We perform a parameter study by varying the magnetized turbulence onset temperature, the accretion stress, the dust mass fraction, and the mass accretion rate. Our models feature a gas-only inner disk, a silicate sublimation front and dust rim starting at around 0.08 au, an ionization transition zone with a corresponding density jump, and a pressure maximum which acts as a pebble trap at around 0.12 au. Migration torque maps show Earth- and super-Earth-mass planets halt in our model disks at orbital periods ranging from 10 to 22 days. Conclusions: Such periods are in good agreement with both the inferred location of the innermost planets in multiplanetary systems, and the break in planet occurrence rates from the Kepler sample at 10 days. In particular, models with small grains depleted produce a trap located at a 10-day orbital period, while models with a higher abundance of small grains present a trap at around a 17-day orbital period. The snow line lies at 1.6 au, near where the occurrence rate of the giant planets peaks. We conclude that the dust sublimation zone is crucial for forming close-in planets, especially when considering tightly packed super-Earth systems.

Fig. 8: Relation between the pebble trap distance and the luminosity of the star. The leftmost red cross is from model MREF and the rest are from our previous work (Flock et al. 2016). The blue diamond shows the position of Trappist-1b and assuming the luminosity of a 1 million year old M dwarf with the mass of M = 0:089 M (Baraffe et al. 2002). eos-nexus.org 11 PROJECT EOS March 15, 2020

Search for L5 Earth Trojans with DECam

Markwardt, Larissa; Gerdes, David W.; Malhotra, Renu; Becker, Juliette C.; Hamilton, Stephanie J.; Adams, Fred C.

Monthly Notices of the Royal Astronomical Society, Volume 492, Issue 4

Most of the major planets in the Solar System support populations of co-orbiting bodies, known as Trojans, at their L4 and L5 Lagrange points. In contrast, Earth has only one known co-orbiting companion. This paper presents the results from a search for Earth Trojans using the DECam instrument on the Blanco Telescope at CTIO. This search found no additional Trojans in spite of greater coverage compared to previous surveys of the L5 point. Therefore, the main result of this work is to place the most stringent constraints to date on the population of Earth Trojans. These constraints depend on assumptions regarding the underlying population properties, especially the slope of the magnitude distribution (which in turn depends on the size and albedo distributions of the objects). For standard assumptions, we calculate upper limits to a 90% confidence limit on the L5 population of NET < 1 for magnitude H < 15.5, NET = 60 − 85 for H < 19.7, and NET = 97 for H = 20.4. This latter magnitude limit corresponds to Trojans ∼300 m in size for albedo 0.15. At H=19.7, these upper limits are consistent with previous L4 Earth Trojan constraints and significantly improve L5 constraints.

Figure 1. The area covered by our survey. The star marks the location of the L5 point. The relative density of synthetic ET objects (see Sec. 5.1) is shown in the background in blue. Each rectangle corresponds to a chip in one of the 8 DECam fields. In total, these fields cover 24 sq. deg. near L5.

eos-nexus.org 12 PROJECT EOS March 15, 2020

Characterization and Properties of Earth-like Planets

Apai, Dániel

Origins: From the Protosun to the First Steps of Life. Proceedings of the International Astronomical Union, Volume 345, pp. 194-201

The search for life in the Universe is intertwined with studies of extrasolar planets aimed at identifying and understanding habitable rocky planets, including those similar in size, bulk composition, planetary environment, and evolution to Earth. The past five years have seen dramatic progress in our understanding of the small (1-4 REarth) planet population. Here we briefly review key results on the occurrence rates of small planets, the first evidence for compositional diversity of these worlds, early results on the characterization of their atmospheres, and the progress toward finding and interpreting potentially habitable planets orbiting the closest stars. We also briefly highlight next steps in furthering our understanding of the origins and properties of habitable worlds.

Figure 1. The transit light source (TLS) effect is the contamination of exoplanet transmission spectra. The effective contamination occurs because the light source of the transmission spectroscopy (transit light chord) has a spectra different from the disk-integrated spectrum of the star (directly observable quantity). TLS can introduce apparent slopes and molecular features in the transmission spectra of planets; the effect is particularly problematic for late-type host stars and small planets. Modified from Rackham et al. (2018).

eos-nexus.org 13 PROJECT EOS March 15, 2020

Cloud Atlas: High-precision HST/WFC3/IR Time-Resolved Observations of Directly-Imaged Exoplanet HD106906b Zhou, Yifan; Apai, Dániel; Bedin, Luigi R.; Lew, Ben W.P.; Schneider, Glenn; Burgasser, Adam J.; Manjavacas, Elena; Karalidi, Theodora; Metchev, Stanimir; Miles-Páez, Paulo A.; Cowan, Nicolas B.; Lowrance, Patrick J.; Radigan, Jacqueline

The Astronomical Journal, Volume 159, Issue 4, id.140

HD106906b is an ~11MJup, ~15Myr old directly-imaged exoplanet orbiting at an extremely large distance from its host star. The wide separation (7.11 arcsec) between HD106906b and its host star greatly reduces the difficulty in direct-imaging observations, making it one of the most favorable directly-imaged exoplanets for detailed characterization. In this paper, we present HST/WFC3/IR time- resolved observations of HD106906b in the F127M, F139M, and F153M bands. We have achieved ~1% precision in the lightcurves in all three bands. The F127M lightcurve demonstrates marginally- detectable (2.7σ significance) variability with a best-fitting period of 4 hr, while the lightcurves in the other two bands are consistent with flat lines. We construct primary-subtracted deep images and use these images to exclude additional companions to HD106906 that are more massive than 4MJup and locate at projected distances of more than ~500 au. We measure the astrometry of HD106906b in two HST/WFC3 epochs and achieve precisions better than 2.5 mas. The position angle and separation measurements do not deviate from those in the 2004 HST/ACS/HRC images for more than 1σ uncertainty. We provide the HST/WFC3 astrometric results for 25 background stars that can be used as reference sources in future precision astrometry studies. Our observations also provide the first 1.4- micron water band photometric measurement for HD106906b. HD106906b's spectral energy distribution and the best- fitting BT-Settl model have an inconsistency in the 1.4-micron water absorption band, which highlights the challenges in modeling atmospheres of young planetary-mass objects.

Figure 1. Direct-imaging observations of the HD106906 system. Left: A demonstration of the two-roll differential imaging results. Red color represents signals from the original images and blue colored pixels are structures from the subtraction model images. Regions that are marked by hatches are used for optimizing the subtraction. HD106906b and a nearby (in projection) uncataloged source (later identified as BG12) are marked in the figure. To avoid the uncataloged source contaminating the photometry for HD106906b, PSF fitting is carried out simultaneously for these two sources. Right: An R (F153M) G (F139M) B (F127M) color composite image of HD106906. Overlaid on the HST RGB composite are the false-color Gemini Planet Imager (inner most) andACS/HRC (outer annulus) scattered light images (Kalas et al. 2015) of the circumstellar disk. The circumstellar disk is not visible in the WFC3/IR images.

eos-nexus.org 14 PROJECT EOS March 15, 2020

The ACCESS Exoplanet Transmission Spectroscopy Survey Apai, D.; Lopez-Morales, M.; Rackham, B. V.; Espinoza, N.; Jordan, A.; Osip, D.; Bixel, A.; McGruder, C.; Kirk, J.; Weaver, I.; Fortney, J.; Rodler, F.; Lewis, N.; Alam, M.

American Astronomical Society meeting #235, id. 174.22

Transmission spectroscopy of transiting exoplanet is currently our most powerful method for exploring the atmospheres of small extrasolar planets. The ACCESS survey is one of the largest ground-based transmission spectroscopy survey of transiting exoplanets. Using the 6.5m Magellan Baade Telescope and its IMACS multi-object spectrographs we have observed exoplanet transits in more than 60 nights over the past five years. The IMACS spectra provide powerful, single-shot 0.4-0.9 micron transmission spectra. In order to provide robust characterization of low-level systematics, we observe multiple (typically 3-5) transits of each target. As of 2019 ACCESS has observed over 20 exoplanets with IMACS, resulting in multiple publications presenting data on planets ranging from sub-neptunes to inflated hot jupiters. ACCESS data provide insights into atmospheric structure, absorbers, and stellar activity. We present here an overview of the ACCESS Survey and its key science results.

eos-nexus.org 15 PROJECT EOS March 15, 2020

Nautilus: A Biosignature Survey in a Thousand Exo-Earths Apai, D.; Milster, T. D.; Kim, D.; Bixel, A.; Schneider, G.; Rackham, B. V.; Liang, R.; Arenberg, J.

American Astronomical Society meeting #235, id. 212.06

An outstanding, multidisciplinary goal of modern science is the study of the diversity of potentially Earth-like planets and the search for life in them. This goal requires a bold new generation of space telescopes, but even the most ambitious designs yet hope to characterize only several dozen potentially habitable planets. Such a sample may be too small to truly understand the complexity of exo-earths. We describe here a notional concept for a novel space observatory designed to characterize a thousand transiting exo-earth candidates. The Nautilus concept [1, 2] is based on an array of inflatable spacecraft carrying very large diameter (8.5 m), very low weight, multi-order diffractive optical elements (MODE lenses) as light-collecting elements. In this concept the mirrors typical to current space telescopes are replaced by MODE lenses with 10 times lighter areal density that are >100 times less sensitive to misalignments, enabling lightweight structure. MODE lenses can be cost-effectively replicated through molding. The Nautilus mission concept has the potential to greatly reduce fabrication and launch costs and mission risks compared to the current space telescope paradigm through replicated components and identical, lightweight unit telescopes. Nautilus is designed to survey transiting exo-earths for biosignatures up to a distance of 300 pc, enabling a rigorous statistical exploration of the frequency and properties of life-bearing planets and the diversity of exo-earths. As the first major step toward realizing this scalable space observatory, we proposed the Nautilus Probe [3], a single Nautilus unit equipped with an 8.5m-diameter lens. The goal of the Nautilus Probe is to carry out a large-scale spectroscopic survey of transiting exoplanets discovered by Kepler, TESS, and - in the near future - by PLATO. Here we will describe the MODE lens technology and provide an overview of the scientific scope and capabilities of the Nautilus mission concept.

eos-nexus.org 16 PROJECT EOS March 15, 2020

The role of planetesimals and gas in the orbital assembly of close-in exoplanets Mulders, G. D.; Ciesla, F.J.; O’Brien, D. P.; Apai, D.; Pascucci, I.

American Astronomical Society meeting #235, id. 224.07

The known population of exoplanets provides us with key information about the formation of planetary systems outside of our own Solar System. In particular, the relative spaces, sizes, and mutual inclinations of planets within planetary systems constrain the amount of gravitational interactions between growing proto-planets and their surroundings. Here, we explore different formation scenarios for the assembly of planetary systems within 1 au around other stars. We compare the demographics of simulated systems to those observed with Kepler, taking into account observation biases using EPOS, the Exoplanet Population Observation Simulator. We find that in all simulated accretion scenarios, planets within a system are of similar size as has been observed with Kepler. However, the planets' relative spacings and mutual inclinations are very sensitive to the amount of orbital damping during formation. Simulated planetary systems formed without any damping effect or with strong damping by gas look different than what is observed by Kepler. On the other hand, systems formed with moderate damping, for example from residual planetesimals, have similar observational characteristics as the Kepler systems.

eos-nexus.org 17 PROJECT EOS March 15, 2020

Hints on the origins of particle traps in protoplanetary disks given by the Mdust − M⋆ relation

Pinilla, Paola; Pascucci, Ilaria; Marino, Sebastian

Astronomy & Astrophysics, Volume 635, id.A105

Demographic surveys of protoplanetary disks, carried out mainly with ALMA, have provided access to a large range of disk dust masses (Mdust) around stars with different stellar types and in different star- forming regions. These surveys found a power-law relation between Mdust and M that steepens in time, but which is also flatter for transition disks (TDs). We performed dust evolution models, which included perturbations to the gas surface density with different amplitudes to investigate the effect of particle trapping on the Mdust − M relation. These perturbations were aimed at mimicking pressure bumps that originated from planets. We focused on the effect caused by different stellar and disk masses based on exoplanet statistics that demonstrate a dependence of planet mass on stellar mass and metallicity. Models of dust evolution can reproduce the observed Mdust − M relation in different star-forming regions when strong pressure bumps are included and when the disk mass scales with stellar mass (case of Mdisk = 0.05 M in our models). This result arises from dust trapping and dust growth beyond centimeter-sized grains inside pressure bumps. However, the flatter relation of

Mdust− M for TDs and disks with substructures cannot be reproduced by the models unless the formation of boulders is inhibited inside pressure bumps. In the context of pressure bumps originating from planets, our results agree with current exoplanet statistics on giant planet occurrence increasing with stellar mass, but we cannot draw a conclusion about the type of planets needed in the case of low-mass stars. This is attributed to the fact that for M < 1M⊙, the observed Mdust obtained from models is very low due to the efficient growth of dust particles beyond centimeter-sizes inside pressure bumps.

Fig. 1. Assumed profiles for the gas surface density distribution when the disk mass is assumed to be 0:05M for all cases.

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The evolution of dust-disk sizes from a homogeneous analysis of 1-10 Myr-old stars Hendler, Nathanial; Pascucci, Ilaria; Pinilla, Paola; Tazzari, Marco; Carpenter, John; Malhotra, Renu; Testi, Leonardo

Accepted for pulication in the Astrophysical Journal

We utilize ALMA archival data to estimate the dust disk size of 152 protoplanetary disks in Lupus (1-3 Myr), Chamaeleon I (2-3 Myr), and Upper-Sco (5-11 Myr). We combine our sample with 47 disks from Tau/Aur and Oph whose dust disk radii were estimated, as here, through fitting radial profile models to visibility data. We use these 199 homogeneously derived disk sizes to identify empirical disk-disk and disk-host property relations as well as to search for evolutionary trends. In agreement with previous studies, we find that dust disk sizes and millimeter luminosities are correlated, but show for the first time that the relationship is not universal between regions. We find that disks in the 2-3 Myr- old Cha I are not smaller than disks in other regions of similar age, and confirm the Barenfeld et al. (2017) finding that the 5-10 Myr USco disks are smaller than disks belonging to younger regions. Finally, we find that the outer edge of the Solar System, as defined by the Kuiper Belt, is consistent with a population of dust disk sizes which have not experienced significant truncation.

Figure 1. Comparison of the ALMA 887 m observation of J16085468-3937431 with our best-fit model. The first panel shows the ALMA observation as a continuum map generated using the CASA clean command with Briggs weighting with a robustness parameter of 0.5. The middle panel shows a continuum map generated from our model using the same UV spacings as the ALMA observation. The last panel shows the residuals between the first two panels (residuals of 3, 5, and 10 sigma are denoted as outlines).

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