Date: Monday 14-Sep-2020
Speaker: Maria Steinrueck (University of Arizona/LPL)
Title: Transport-induced disequilibrium chemistry and photochemical hazes in hot Jupiter atmospheres: Insights from 3D simulations
Out of all exoplanets, hot Jupiters are the most amenable to atmospheric characterization. To make sense of the growing body of observations and to better understand the atmospheres of these planets, three-dimensional models are crucial. The strong day-night temperature contrast on hot Jupiters drives a vigorous atmospheric circulation which can profoundly change chemical processes and cloud/haze formation. In turn, changed abundances have a feedback on the temperature structure and the winds. In this talk, I will highlight two examples of this interaction between chemistry (in a broad sense) and the atmospheric circulation. First, I will talk about including disequilibrium abundances of the important infrared absorbers CH4 and CO in general circulation models (GCMs). My results show that disequilibrium CH4 and CO abundances significantly affect the thermal structure, predicted phase curves and emission spectra of hot Jupiters. In the second part of the talk, I will present results on the 3D distribution of photochemical hazes and discuss implications for transit spectroscopy.
For further information contact PALS coordinator Dr. Lori Feaga at feaga@astro.umd.edu or (301)-405-1383.
Date: Monday 21-Sep-2020
Speaker: Sam Crossley, with discussion by all
Title: Delivery of Earth's Water, a new hypothesis
Sam Crossley will lead a discussion on a recent publication in Science Magazine that suggests Earth's water may have been delivered by enstatite chondrites rather than the previously favored carbonaceous chondrites. Sam will briefly start the discussion by summarizing the paper, however, the discussion is open for all to participate. If you are interested in reading the paper ahead of time, the reference is Piani et al. 2020. Earth’s water may have been inherited from material similar to enstatite chondrite meteorites. Science 369, 1110-1113.
For further information contact PALS coordinator Dr. Lori Feaga at feaga@astro.umd.edu or (301)-405-1383.
Date: Monday 05-Oct-2020
Speaker: Sarah Moran (JHU)
Title: Clouds and Haze of sub-Neptune Worlds from the Lab
Little experimental laboratory work has been done to explore the properties of photochemical hazes formed in exoplanets, despite their role in atmospheric chemistry and their subsequent possible impact on observations, both for those of current observatories like Hubble and in the future with JWST and ground-based observatories. I will present results of the composition of haze particles produced from exoplanet laboratory studies in the JHU PHAZER laboratory. Many complex molecular species with general chemical formulae CwHxNyOz were detected in the haze particles, including those with prebiotic applications, such as the formulae for amino acids, nucleobases, and simple sugars. I will discuss the implications of these chemical measurements as they compare to existing atmospheric models of exoplanet photochemistry. Additionally, the experimental exoplanetary haze analogues exhibit diverse physical properties, which may help us understand their role as potential cloud condensation nuclei and their role in subsequent atmospheric evolution. Finally, I will discuss how we can apply what we’ve learned from the laboratory into atmospheric models for existing and future observations of sub-Neptune-sized exoplanets.
For further information contact PALS coordinator Dr. Lori Feaga at feaga@astro.umd.edu or (301)-405-1383.
Date: Monday 19-Oct-2020
Speaker: Joe DeMartini (UMD)
Title: The Motion of Surface Grains in Low Gravity Environments: Applications to Apophis, The Lunar Brazil-nut Effect, and Low-G Seismic Wave Propagation
The recent OSIRIS-REx and Hayabusa2 missions have shown the surfaces of rubble piles to be complex assemblies of grains ranging from sub-mm to meters in size. One of the best ways at understanding the physics occurring on these surfaces is using simulations. Our group is using the parallel N-body gravity tree code PKDGRAV to simulate granular dynamics in low-gravity on the surfaces of planetary and asteroidal bodies. In this talk, I will highlight three of our projects that focus on the motion of grains at or near the surface of bodies with overlying regolith layers. First, I will discuss our simulations (still in progress) to confirm laboratory experiments measuring the propagation speed of a seismic wave through a granular medium under different confining pressures. Then I will go over our recent project investigating the effects of particle shape on the vertical rise time of a large subsurface intruder in response to seismic influences by the Brazil-nut Effect -- a phenomenon which has mostly been investigated using spherical grains in both laboratory and simulated experiments. Finally, I will show the results of our simulations of the 2029 Apophis close encounter, with a focus on the expected dilation and spin change of the body during the close approach and what expected results one may see from a potential mission (in-situ or otherwise) focusing on Apophis during its upcoming perigee passage.
For further information contact PALS coordinator Dr. Lori Feaga at feaga@astro.umd.edu or (301)-405-1383.
Date: Monday 02-Nov-2020
Speaker: Dan Moriarty (GSFC)
Title: Evidence for a Stratified Upper Mantle Preserved within the Moon's South Pole - Aitken Basin
Like the Earth, the Moon is layered into a crust and mantle. The Moon's layering was shaped by an early global melting event known as the "Lunar Magma Ocean." As the magma ocean solidified, dense minerals sank to form the mantle, while less-dense minerals floated to form the crust. Elements such as thorium do not easily incorporate into mineral structures, and remain in the liquid. Because of this, a thorium-rich dreg layer was sandwiched between the crust and mantle. These dregs are very dense and are expected to sink into the lower mantle during or soon after crystallization. We have discovered that the Moon's largest and oldest impact basin excavated material from this dense, thorium-rich layer before it sank. The exposed material was then diluted and obscured by four billion years of impactcratering and volcanic eruptions. However, we have identified several pristine exposures created by recent craters. The impact basin also melted rocks from greater depths than the rocks it ejected. These melted rocks exhibit a much different composition. This indicates that the lunar upper mantle included two compositionally-distinct layers that were exposed in different ways by this large impact event. These results have important implications for understanding the formation and evolution of the Moon.
For further information contact PALS coordinator Dr. Lori Feaga at feaga@astro.umd.edu or (301)-405-1383.
Date: Monday 09-Nov-2020
Speaker: Tony Farnham
Title: Results from the 2018/2019 Close Approach of Comet 46P/Wirtanen
Comet 46P/Wirtanen is a Jupiter family comet that made an historically close approach to the Earth in December 2018, reaching naked-eye brightness for several weeks. This apparition provided an excellent opportunity for measuring the comet's physical properties and characterizing its behavior. We extensively observed Wirtanen over a 3-month period around close approach, allowing us to investigate the temporal changes in the comet's activity and dynamical properties. Our results show that the comet's rotation rate changed throughout the perihelion passage, indicating that the activity is inducing significant torques on the nucleus. We will also discuss several outbursts that were detected over the course of the apparition.
For further information contact PALS coordinator Dr. Lori Feaga at feaga@astro.umd.edu or (301)-405-1383.
Date: Monday 16-Nov-2020
Speaker: Adeline Gicquel-Brodtke (UMD)
Title: Activity of comet 67P/Churyumov- Gerasimenko during the summer of 2015 with Rosetta
The ESA Rosetta spacecraft reached comet 67P/Churyumov-Gerasimenko (67P) in August 2014, and over the course of the 2.5-year mission, many outbursts were seen. Close to perihelion in August 2015, a display of 34 outbursts on 67P (Vincent et al. 2016) were observed with the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) and the Navigation Camera (NAVCAM).
We focused on a bright outburst observed with the OSIRIS camera on July 29, 2015 (Gicquel et al. 2017). Using a Direct Simulation Monte Carlo (DSMC) model of gas and dust trajectories close to the nucleus, we estimated what gas properties were needed to create the dust distribution seen in the images. We find that, to fit the dust data, the gas production rate should be about 10x higher at the source location of the outbursts than neighboring areas.
We improved on this initial effort by updating an existing Collisionless Gas Simulation at JPL to provide estimates for the water outgassing flux and gas temperature. We are improving our current dust simulation to account for optically thick conditions. We will assume different size distribution and compositions for the dust. This will allow us to better constrain the nature of the outburst (gas-to-dust ratio, distribution of gas and dust, radial profile, brightness) and the surface properties which shape the appearance of the outburst (e.g. size of the active region on the nucleus).
For further information contact PALS coordinator Dr. Lori Feaga at feaga@astro.umd.edu or (301)-405-1383.
Date: Monday 30-Nov-2020
Speaker: Diana Powell
Title: Protoplanetary Disks and Clouds in Substellar Atmospheres: Insights from Microphysics
In this talk, I will provide evidence that protoplanetary disks are more than an order of magnitude more massive than previously appreciated, that the detailed properties of clouds shape observations of substellar atmospheres, and that the physics of modeling clouds gives a new understanding of the solid content in protoplanetary disks. Clouds on extrasolar worlds are seemingly abundant and interfere with observations; however, little is known about their properties. In our modeling, we predict cloud properties from first principles and investigate how the interesting observational properties of hot Jupiters and brown dwarfs can be explained by clouds. Next, I will report on a new set of models that reconcile theory with observations of protoplanetary disks and create a new set of initial conditions for planet formation models. The total mass available in protoplanetary disks is a critical initial condition for understanding planet formation, however, the surface densities of protoplanetary disks still remain largely unconstrained due to uncertainties in the dust-to-gas ratio and CO abundance. I make use of recent resolved multiwavelength observations of disks in the millimeter to constrain the aerodynamic properties of dust grains to infer the total disk mass without an assumed dust opacity or tracer-to-H2 ratio. Finally, I will present new 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 well-studied disks 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.
For further information contact PALS coordinator Dr. Lori Feaga at feaga@astro.umd.edu or (301)-405-1383.
Date: Monday 07-Dec-2020
Speaker: Erin May (JHU/APL)
Title: Observations of Exoplanet Atmospheres: what have we learned and where do we go from here?
The impending launch of JWST brings with it the unparalleled abilities to characterize the atmospheres of rocky worlds. But are we ready? While most ground-based and Spitzer observations to-date have primarily focused on larger, gaseous planets, lessons learned in systematic removals and data analysis will inform the methods with which we recover the signals from terrestrial planets. Of course, the ability to observe rocky worlds brings with it a need for updated modeling schemes that take into account the various subtleties involved in the spectra of small planets. 3D modeling predictions for classifying terrestrial and mini-Neptune atmospheres will allow us to identify interesting rocky targets for follow up, while predictions for the impact of cloud variability on transmission and emission observations with JWST will inform best-practices for multi-epoch observations. The increased complexities of terrestrial atmospheres means we have more puzzle pieces to consider, but by starting with what we know from our work with larger targets, we may just have a hope of detecting molecular abundances in rocky, potentially habitable worlds, in the near future.
For further information contact PALS coordinator Dr. Lori Feaga at feaga@astro.umd.edu or (301)-405-1383.
