List of Past Planetary Astronomy Lunches (PALS) : 01-Sep-2016 to 31-Dec-2016


Date:   Monday 29-Aug-2016
Speaker:   Dr. Murthy Gudipati (NASA Jet Propulsion Laboratory)
Title:  "Radiation-induced Production of Near-Surface Volatiles on Simulated Europa's Surface"

Europa's surface is heavily bombarded with Jovian magnetospheric radiation, which includes high-energy electrons that penetrate far deeper than the other ionic species such as H+, O+, and S+. However, both electrons and ions cause surface sputtering that results in ejection of neutral and ionic atoms, molecules, clusters, and large ice particles that are sometimes also known as "dust" particles. These volatile gases and non-volatile ices form Europa's tenuous atmosphere, providing an opportunity to determine Europa's surface composition while flying over Europa. NASA's planned Europa Mission (https://www.nasa.gov/europa) is aimed at doing precisely this using two instruments on board SUDA and MASPEX (http://www.nasa.gov/press-release/nasa-s-europa-mission-begins-with-selection-of-science-instruments), while a suite of other instruments interrogates surface and interior, all together to address the big picture of "Europa's Habitability". This talk summarizes expected near-surface volatiles on Europa based on laboratory experimental simulations.

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 05-Sep-2016
Speaker:   LABOR DAY
Title:  NO PALS

NO PALS

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 12-Sep-2016
Speaker:   Ashlee Wilkins (UMD)
Title:  Transiting Exoplanet Case Studies with Hubble

I will present a study of the atmospheres of four transiting giant planets (HAT-3, HATS-7, HD 149026, and WASP-18) as observed by the Hubble Space Telescope's Wide-Field Camera-3 in spatial scan mode, along with a brief digression into a discussion of the tidal orbital decay for WASP-18b. We analyze observations in a near-infrared band dominated by strong water absorption features. As part of a larger Hubble program, our group and others are working to advance the state of exoplanet atmosphere observations from single, planet-by-planet, case studies, to an understanding of the large, hot, gaseous planets as a population. Though these planets may be rare, their observability represents a unique opportunity to probe planet formation mechanisms, as well as atmospheric structures in a high-irradiation environment. These observations could also yield insights into aerosols in the atmosphere; the behavior of the aerosols (i.e. clouds and/or hazes) could significantly impact atmospheric chemistry and observational signatures, and we as a community must get a better handle on the phenomenon of aerosols in advance of the next generation of space observatories, including JWST and WFIRST.

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 19-Sep-2016
Speaker:   Mike Hankey (American Meteor Society)
Title:  The Eye Witness Fireball Reporting System

Mike Hankey is operations manager from the American Meteor Society (AMS). He will explain the eye witness fireball reporting system, trajectory calculations, NEXRAD meteorite recovery and the AMS's new Fireball Camera Program.

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 26-Sep-2016
Speaker:   Aki Roberge (GSFC)
Title:  Probing the Composition of Planetary Material: Transits of Star-Grazing Exocomets

Observations of protoplanetary disks shed light on the composition of the primordial material that goes into making planets. But probing the bulk composition of the outcomes of the planet formation process is extremely challenging, if not impossible in many cases. Debris disks around nearby stars provide a nearly unique opportunity to examine the composition of material that has already been incorporated into extrasolar planetesimals, then ejected back out again through evaporation and mutual collisions. In this talk, I'll review what's known about exocomets in debris disk systems through observations as they transit their host stars. Optical spectroscopy has revealed the frequency of the events and their dynamical character, including evidence for comet families in one well-studied system. In the best cases, the composition of the evaporating material in their comae has been probed primarily with UV absorption spectroscopy. Surprisingly, those observations show super-solar carbon abundance in the gas coming from star-grazing exocomets around high mass stars, which is currently unexplained as the host stars have solar metallicity.

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 03-Oct-2016
Speaker:   Bradley T De Gregorio, U.S. Naval Research Laboratory
Title:  Diversity of Organic Matter in Comets: Results from 81P/Wild 2

Carbonaceous matter is a major component of comets. However, it is difficult to reliably characterize macromolecular CHON material, due to limitations of spacecraft instrumentation, terrestrial contamination, or alteration during sampling. In this talk I will discuss the variety of organic chemistries observed in cometary CHON matter returned by the NASA Stardust mission to 81P/Wild 2, ranging from polymer-like material to graphitic material and diamond. During the preliminary examination phase, several extreme chemistries (N-rich, O-rich, etc.) were observed, suggesting comets are a unique reservoir for carbonaceous phases among planetary bodies. D and 15N isotopic anomalies were also observed, indicating a likely interstellar origin. However, further characterization by transmission electron microscopy (TEM) has shown that these extreme N-rich and O-rich organics are contaminants, and the majority of the Wild 2 carbonaceous samples have isotopic compositions consistent with a solar system origin. Some of the Wild 2 organics show signatures of aliphatic carbon, but except for one example, all of these samples show some amount of interaction with aerogel during capture or epoxy during sample preparation. It is unclear if the high aliphatic signatures are due to chemical fractionation or alteration during capture. Fourteen verified samples of unaltered cometary CHON matter look similar to that found in chondrites and IDPs, albeit still with a wider range of functional chemistry. These contain two examples of poorly graphitized carbon, whose presence in Wild 2 was implied by Raman observations but dismissed as capture heating. Nanoglobule morphologies have also been observed in at least three captured grains.

There are two outstanding questions that arise from these results. First, compared with primitive carbonaceous chondrites and IDPs, the abundance of presolar/interstellar organic matter appears much too low in Wild 2. While the nature of hypervelocity capture into silica aerogel creates a sampling bias against all carbonaceous matter relative to silicates, it cannot explain the apparent overabundance of isotopically "solar" CHON material. This may be a clue regarding the homogenizing extent of particle transport in the early Solar Nebula. Secondly, it is unclear if any of the macromolecular CHON matter formed in situ on the comet. Formaldehyde polymers have been shown to form globular morphologies when exposed to liquid water. However, organic nanoglobules in Wild 2 contain abundant aromatic carbon bonding, inconsistent with an origin from POM-like precursors.

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 10-Oct-2016
Speaker:   DPS Practice Talks
Title:  TBA

Abstract TBA

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 17-Oct-2016
Speaker:   DPS
Title:  NO PALS

NO PALS

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 24-Oct-2016
Speaker:   [Regular UMD Colloquium on Oct 26: Hal Weaver (APL)]
Title:  NO PALS-Attend UMD Colloquium

NO PALS

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 31-Oct-2016
Speaker:   Jared Espley (GSFC)
Title:  Space weather and atmospheric loss at Mars: Initial results from MAVEN

Mars lacks an intrinsic planetary magnetic field but has very strong localized crustal fields. Therefore, the solar wind interacts directly with the dynamic martian ionosphere creating a time-variable induced magnetosphere. This complex interaction leads to erosion of the martian atmosphere and is the leading hypothesis of how Mars went from a comparatively warm, wet, and habitable ancient environment to the cold, dry, inhospitable environment we see today. I report on results from the first Mars-year of MAVEN observations of this environment. I discuss our initial estimates of atmospheric loss, the relative impact of the large solar (and cometary!) events vs. the impact of the steady-state solar wind, and the dynamics of this complex environment.

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 07-Nov-2016
Speaker:   Neil Dello Russo (APL)
Title:  Emerging Trends and a Comet Taxonomy Based on the Volatile Chemistry Measured in Thirty Comets With High-Resolution Infrared Spectroscopy

A systematic analysis of the mixing ratios with respect to H2O for eight species (CH3OH, HCN, NH3, H2CO, C2H2, C2H6, CH4, and CO) measured with high-resolution infrared spectroscopy in thirty comets between 1997 and 2013 is presented. Some trends are beginning to emerge when mixing ratios in individual comets are compared to average mixing ratios obtained for all species within the population. The variation in mixing ratios for all measured species is at least an order of magnitude. Overall, Jupiter-family comets are depleted in volatile species with respect to H2O compared to long-period Oort cloud comets, with the most volatile species showing the greatest relative depletion. There is a high positive correlation between the mixing ratios of HCN, C2H6, and CH4 , whereas NH3, H2CO, and C2H2 are moderately correlated with each other but generally uncorrelated or show only weak correlation with other species. CO is generally uncorrelated with the other measured species possibly because it has the highest volatility and is therefore more susceptible to thermal evolutionary effects. Measurements suggest that molecular mixing ratios for CH3OH, HCN, C2H6, and CH4 remain relatively constant inside a heliocentric distance of about 2 AU suggesting a dominant ice source, whereas mixing ratios of NH3, H2CO, and C2H2 increase inside heliocentric distances of about 0.8 AU, suggesting the possibility of additional sources related to the thermal decomposition of organic dust. Although this provides indirect information on the composition of the most volatile grains in comets, it presents an additional difficulty in classifying comet chemistry because most comets within this dataset were only observed over a limited range of heliocentric distance. Although there is remarkable compositional diversity resulting in a unique chemical fingerprint for each comet, a hierarchical tree cluster analysis is used to determine a reasonable but arbitrary taxonomic classification system containing four groups and eleven subgroups. Optical and infrared comparisons indicate that mixing ratios of daughter species and potential parents from cometary ices are sometimes but not always consistent with one another. This suggests that in many comets there are significant sources of C2 and/or CN from grains, and that the importance of these sources is variable within the comet population.

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 14-Nov-2016
Speaker:   NO PALS
Title:  NO PALS

Abstract TBA

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 21-Nov-2016
Speaker:   NO PALS
Title:  NO PALS

Abstract TBA

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 28-Nov-2016
Speaker:   Patrick Peplowski (APL)
Title:  The formation and early evolution of Mercury as revealed by MESSENGER

Mercury is the end-member terrestrial planet in most regards, including size, density, composition, and proximity to the sun. Its ancient surface preserves a record of the earliest history of our solar system, information that has been lost on the highly processed crusts of Venus, Earth, and Mars. As a result, Mercury provides a unique opportunity to test our understanding of terrestrial planet formation and evolution. The MESSENGER mission, which recently concluded the first orbital survey of Mercury, has revolutionized our view of the innermost planet. MESSENGER revealed a surface shaped by extensive volcanic activity, composed of materials with exceptionally low iron content, significant quantities of moderately volatile materials (Na, S, K, Cl), and weight percent levels of carbon. These observations are strikingly distinct from predicted crustal compositions based on pre-MESSENGER theories for Mercury’s formation. I will present the results of the MESSENGER geochemical measurements, and discuss the emerging view of Mercury’s formation and early evolution and how it fits into current models for terrestrial planet formation.

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 05-Dec-2016
Speaker:   No PALS
Title:  No PALS

Abstract TBA

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 12-Dec-2016
Speaker:   Geronimo Villanueva (GSFC)
Title:  PSG: An online tool for synthesizing spectra of planets, exoplanets and small bodies from any telescope/mission

The Planetary Spectrum Generator (PSG) is an online tool for synthesizing planetary spectra (atmospheres and surfaces) for a broad range of wavelengths (0.1 μm to 100 mm, UV/Vis/near-IR/IR/far-IR/THz/sub-mm/Radio) from any observatory (e.g., JWST, ALMA, Keck, SOFIA), any orbiter (e.g., MRO, ExoMars, Cassini, New Horizons), or any lander (e.g., MSL). This is achieved by combining several state-of-the-art radiative transfer models, spectroscopic databases and planetary databases. The tool includes a 1) 3D (three-dimensional) orbital calculator for any solar system body and all confirmed exoplanets; 2) The tool ingests billions of spectral lines and optical constants from almost 1,000 chemical species and ices/solids; 3) It contains realistic instrument/telescope models and noise/SNR calculators for coronographs, interferometers (e.g. ALMA), space orbiters, etc; 4) The code calculates terrestrial transmittances for a broad range of conditions (altitude and water vapor columns, SOFIA, balloons). A short introduction and a live-demo will be given.

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


Date:   Monday 19-Dec-2016
Speaker:   TBA
Title:  TBA

Abstract TBA

For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.


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