List of Past Planetary Astronomy Lunches (PALS) : 01-Sep-2019 to 31-Dec-2019

Date:   Monday 09-Sep-2019
Speaker:   Eliza Kempton (UMD)
Title:  Revealing Exoplanet Atmospheres in 3-D

In the upcoming era of JWST and 30-meter class ground-based telescopes we will be forced to reckon with the full 3-D nature of extrasolar planets.  Today, many current models treat exoplanet atmospheres in one dimension, as a vertically stratified global average -- similar to 1-D models of stars and many solar system planets.  Yet we know that close-in transiting exoplanets in particular are expected to be tidally locked to their host stars with short radiative timescales in their atmospheres, and should therefore have strong longitudinal inhomogeneities in their temperature structure, composition, and atmospheric dynamics.  I will present models and observations of exoplanet atmospheres that take into account their 3-D structure, focusing on how we can recover key physical, chemical, and dynamical properties.  I will spend considerable time discussing the constraints on atmospheric circulation that can be obtained through high resolution spectroscopy (R~10^5), which allows for individual spectral lines to be resolved and for atmospheric motions to be directly probed through Doppler-shifted line profiles.  This observational technique will reach its full potential with the planned complement of high-resolution spectrographs on upcoming 30-meter class ground-based telescopes.

For further information contact PALS coordinator Dr. Lori Feaga at or (301)-405-1383.

Date:   Monday 07-Oct-2019
Speaker:   Quanzhi Ye (UMD)
Title:  Asteroids falling into the Sun

The under-abundance of asteroids on orbits with small perihelion distances suggests that thermally-driven disruption may be an important process in the removal of rocky bodies in the solar system. Here I will discuss how the debris streams arise from possible thermally-driven disruptions in the near-Sun region based on simulations of the disruption of near-Sun asteroids, and how can we use meteor data to understand the asteroid disruptions near the Sun. I will show that there is a clear overabundance of Sun-approaching meteor showers, which is best explained by a combined effect of comet contamination and an extended disintegration phase that lasts up to a few thousand years. Finally, I will briefly describe the recent search of near-Sun asteroids with the Zwicky Transient Facility Survey, as well as the implication of our finding for the study of exoplanetary systems.

For further information contact PALS coordinator Dr. Lori Feaga at or (301)-405-1383.

Date:   Wednesday 16-Oct-2019
Speaker:   Hannah Jang-Condell (University of Wyoming)
Title:  Exoplanet Science at the University of Wyoming

The University of Wyoming is home to the 2.3-m Wyoming Infrared Observatory (WIRO) and the 0.6-m Red Buttes Observatory (RBO). In this talk I will discuss some of the research projects on exoplanet science that are carried out on these facilities. Much of our observational efforts focus on follow-up of exoplanet candidates discovered by TESS. I will also discuss new instrumentation being built that will enable new observational capabilities at WIRO for exoplanet discovery and characterization.

For further information contact PALS coordinator Dr. Lori Feaga at or (301)-405-1383.

Date:   Monday 21-Oct-2019
Speaker:   Adam McKay (GSFC)
Title:  The Peculiar Volatile Composition of CO-Dominated comet C/2016 R2 (PanSTARRS)

Comet C/2016 R2 (PanSTARRS) has a peculiar volatile composition, with CO being the dominant volatile, as opposed to H2O, and one of the largest N2/CO ratios ever observed in a comet. Using observations obtained with the Spitzer Space Telescope, NASA’s IRTF, the 3.5 m Astrophysical Research Consortium telescope at Apache Point Observatory, the Discovery Channel Telescope at Lowell Observatory, and the Arizona Radio Observatory 10 m Submillimeter Telescope, we quantified the abundances of 12 different species in the coma of R2 PanSTARRS. We confirm the high abundances of CO and N2 and heavy depletions of H2O, HCN, CH3OH, and H2CO compared to CO reported by previous studies. We provide the first measurements (or most sensitive measurements/constraints) on H2O, CO2, CH4, C2H6, OCS, C2H2, and NH3, all of which are depleted relative to CO by at least 1─2 orders of magnitude compared to values commonly observed in comets. The observed species also show strong enhancements relative to H2O, and, even when compared to other species like CH4 or CH3OH, most species show deviations from typical comets by at least a factor of 2─3. The only mixing ratios found to be close to typical are CH3OH/CO2 and CH3OH/CH4. While R2 PanSTARRS was located at a heliocentric distance of 2.8 au at the time of our observations in 2018 January/February, we argue, using sublimation models and comparison to other comets observed at similar heliocentric distance, that this alone cannot account for the peculiar observed composition of this comet and therefore must reflect its intrinsic composition. We discuss possible implications for this clear outlier in compositional studies of comets obtained to date and encourage future dynamical and chemical modeling in order to better understand what the composition of R2 PanSTARRS tells us about the early solar system. We also present preliminary analysis of post-perihelion observations obtained with Spitzer, Keck HIRES, and NASA's IRTF that show the peculiar coma composition of R2 PanSTARRS is not limited to the pre-perihelion portion of the orbit sampled by previous observations, but is an intrinsic property of the comet. We also discuss possible implications for compositional heterogeneity in R2 PanSTARRS.

For further information contact PALS coordinator Dr. Lori Feaga at or (301)-405-1383.

Date:   Friday 01-Nov-2019
Speaker:   James Owen (Imperial College)
Title:  The origin of close-in exoplanets

The observed exoplanet population unveiled by recent detection programs is billions of years old, distinctly separated in time from the planet formation process that only lasted ~10-100 Myr. I will argue that atmospheric escape has been one of the key evolutionary drivers shaping the exoplanet population we observe today. By understanding how these planets evolve in time, I will show we can place some intriguing constraints on how they formed.

For further information contact PALS coordinator Dr. Lori Feaga at or (301)-405-1383.

Date:   Monday 04-Nov-2019
Speaker:   Doug Hemingway (Carnegie DTM)
Title:  Icy ocean world interiors - techniques and implications

The discovery of icy ocean worlds within our own solar system has raised several important questions. Might these worlds, with their potentially habitable subsurface oceans, present our most promising opportunity for discovering life beyond Earth? More basically, how do we know the extent of these internal oceans, or that they are even present at all? Are these oceans a persistent or transient phenomenon? With an emphasis on Saturn's small but surprisingly active moon Enceladus, I will show how, even with limited topography and gravity field information, we can place constraints on the interior structures and thermal states of these fascinating little worlds. At the same time, however, I will show that there are many important questions that remain open.

For further information contact PALS coordinator Dr. Lori Feaga at or (301)-405-1383.

Date:   Monday 11-Nov-2019
Speaker:   Nestor Espinoza (STScI)
Title:  Transiting exoplanets: detection and characterization in the era of TESS and JWST

Transiting exoplanets are exciting objects to study because, with sufficient follow-up, detailed characterization can be performed which can reveal fascinating details about the formation and evolution of these distant worlds. Atmospheric characterization, in particular, is one of the most appealing ones as it can provide key information to understand how these exoplanets interacted with the protoplanetary disks and stellar environment in which they lived and formed. Despite this exciting opportunity, the number of transiting exoplanets "optimal" for atmospheric characterization is still a small fraction (~1%) of the confirmed transiting exoplanets detected to date. Their detection is, thus, as important as their actual characterization if we want to build representative samples of exoplanets in order to unveil the physics behind their formation and evolution. In this talk, I will present the opportunities the TESS mission presents for the search and characterization of those interesting "optimal" transiting exoplanets with JWST in the horizon, along with our on-going efforts on this search, with a special focus on gas giant exoplanets. I will then focus on current synergies with ground-based facilities for atmospheric characterization that are achieving HST-like precision on both southern and northern hemispheres, and which will enable a panchromatic view of the atmospheres of exoplanets to be characterized with JWST. New avenues for the characterization of these distant worlds in light of these present and upcoming high-precision facilities will be discussed, along with the physical pictures these might help reveal.

For further information contact PALS coordinator Dr. Lori Feaga at or (301)-405-1383.

Date:   Monday 18-Nov-2019
Speaker:   Tilak Hewagama (UMD/GSFC)
Title:  Chasing an Oort Cloud Comet and Instruments for Planetary Science

Primitive Object Volatile Explorer (PrOVE) is a SmallSat mission concept to study the surface morphology and volatile inventory of an Oort cloud comet in its first perihelion passage phase when volatile activity is near peak. SmallSat infrastructure imposes limits on propulsion systems, which are compounded by sensitivity to the spacecraft disposal state from the launch platform and potential launch delays. We propose circumventing launch platform complications by using waypoints in space to park a deep space SmallSat while awaiting the opportunity to enter a trajectory to flyby a suitable target. Two low risk instruments are baselined: a mutlispectral camera to characterize non-thermal fluorescence from coma volatiles (H2O, CO2, CO, and organics) and nucleus thermal emission; a high spatial broadband imaging camera. The ESA Comet Interceptor is an implementation of a conventional spacecraft in an F-Class mission.

In partnerships with GSFC, UMD researchers are involved in developing instruments that span the UV through THz spectral regions. We will discuss some of these optical instruments which include remote sensing spectrometers and radiometers for pushbroom orbiting spacecraft, and landed vibrational instruments such as Raman and infrared reflectance spectrometers. Science goals span physics, chemistry, and dynamics of atmospheres; surface morphology, mineralogy, and thermal inertia; exploration of macromolecules of interest in astrobiology; and setting stage for lunar In Situ Resource Utilization. Science targets include Earth, Solar System planets, moons, comets, and asteroids.

For further information contact PALS coordinator Dr. Lori Feaga at or (301)-405-1383.

Date:   Monday 25-Nov-2019
Speaker:   Julian Marohnic (UMD)
Title:  Constraining the merger of the contact binary Arrokoth (2014 MU69) with soft-sphere discrete element simulations

The New Horizons mission has returned stunning images of the bilobate Kuiper belt object 2014 MU69 (now officially known as Arrokoth). It is a contact binary, formed from two intact and seemingly undisturbed predecessor objects joined by a narrow contact region. We use an N-body code to model a variety of possible merger scenarios with the aim of constraining how 2014 MU69 may have evolved from two Kuiper belt objects into its current contact binary configuration.

For further information contact PALS coordinator Dr. Lori Feaga at or (301)-405-1383.

Date:   Monday 09-Dec-2019
Speaker:   Matthew Knight (UMD)
Title:  1I/'Oumuamua, 2I/Borisov and the Emerging Field of Interstellar Objects

The discovery of 1I/'Oumuamua in 2017 was the culmination of decades of searches for the first interstellar visitor to our solar system. Our second interstellar visitor, and the first unambiguously interstellar comet, 2I/Borisov was discovered in August 2019 and is currently the subject of a world-wide observing campaign. I will review what is known about Borisov to date and highlight the studies being conducted by our group at UMD, including observations with the Discovery Channel Telescope, the ZTF, the VLT, and the Hubble Space Telescope. I will then discuss the new investigations that are being enabled by the discovery of two interstellar objects and where such inquiries may go over the next decade.

For further information contact PALS coordinator Dr. Lori Feaga at or (301)-405-1383.

Date:   Monday 16-Dec-2019
Speaker:   Thomas Fauchez (GSFC)
Title:  From Climates to Biosignatures: Comparative Planetology within the TRAPPIST-1 System

The TRAPPIST-1 system will be a prime target for atmospheric characterization with JWST due to the small size of the host star, its relative proximity to the Earth and frequent transits of the seven planets. Three planets are in the habitable zone of the system, namely TRAPPIST-1e, 1f and 1g. The planet being the one most likely to be habitable, receiving the right amount of stellar flux to allow liquid water on the surface across a large range of atmospheric configurations. However, the detectability of atmospheric molecular species may be severely impacted by the presence of clouds and/or hazes in their atmosphere.

In this work, we performed 3-D Global Climate Model (GCM) simulations with the LMD Generic model supplemented by 1-D photochemistry simulations at the terminator with the Atmos model to simulate several possible atmospheres for TRAPPIST-1e, 1f and 1g: 1) CO2 rich atmospheres, 2) Archean Earth, and 3) modern Earth with a focus on TRAPPIST-1e. JWST synthetic transit spectra were computed using the GSFC Planetary Spectrum Generator (PSG).

We show that the use of 3-D Global Climate Models, taking self-consistentcy into account for the effect of clouds and sub-saturation, is crucial to evaluatng the detectability of atmospheric molecules of interest as well as interpreting in a more global approach (and thus robust and relevant) future detections. We find that TRAPPIST-1e, 1f and 1g atmospheres, with clouds and/or hazes, could be detected with the NIRSpec prism from the CO2 absorption line at 4.3 μm in less than 15 transits at 3σ or less than 30 transits at 5σ. This number of transits is reasonably achievable during JWST's life time. However, our analysis suggests that other gas such as O2, O3, CO, CH4 would require hundreds (or thousands) of transits to be detectable. We also find that H2O, mostly confined in the lower atmosphere, is very challenging to detect for these planets or similar systems if the planets' atmosphere is not in a moist greenhouse state.

These preliminary results therefore address the weaknesses of JWST's ability to characterize habitable exoplanets. Advances required beyond JWST to detect the atmosphere of a habitable exoplanet are discussed in reference to the status of future observatories and their proposed design strategies, highlighting the importance of instrument stability, aperture size and wavelength range.

For further information contact PALS coordinator Dr. Lori Feaga at or (301)-405-1383.

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