List of Past Planetary Astronomy Lunches (PALS) : 01-Sep-2009 to 31-Dec-2009


Date:   Thu, 02-Jul-2009
Speaker:   Nelly Mouawad (UMD)
Title:  Na Variations in Mercury's Exosphere around the first MESSENGER Flyby

Abstract: I will present Ground-based observations of the sodium exospheric emission at Mercury taken at the McMath-Pierce Solar Telescope at Kitt Peak, Arizona. These were conducted during the period of January 10-18, 2008. This dataset brackets observations taken with the Ultraviolet and Visible Spectrometer (UVVS) on The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument on board the MESSENGER spacecraft during the first flyby of the planet, January 14, 2008.

From the ground, we observed strong temporal and spatial variability of the sodium emission on the dayside of the planet . Variations of the sodium D2 emission were observed peaking at different regions of the dayside exosphere near the sub solar point and/or near one or both poles. There was little north-south asymmetry in the ground-based dayside sodium exosphere on January 14 but there was an indication of a possible asymmetry observed in the tail by MASCS.

These data are analyzed in terms of the different source processes that are in play. Photon-stimulated desorption of sodium is expected to induce a maximum sodium density near the sub solar point. Sputtering in the polar cusps should produce high latitude sodium emissions, but solar radiation pressure may also sweep sodium to high latitudes, and impact vaporization by meteorites and meteors would induce local and transient density enhancements in the exosphere.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 16-Jul-2009
Speaker:   Matthew Knight (Lowell Observatory)
Title:  Rotational Study of Comets C/2007 N3 Lulin and 10P/Tempel 2

Abstract: I will discuss ongoing analysis of Comets C/2007 N3 Lulin and 10P/Tempel 2. Both comets were observed using optical broadband and narrowband filters at Lowell Observatory. Dynamically new comet Lulin was observed monthly from January-May 2009. Using coma morphology from January and February, we determined a rotation period of ~42 hours, the approximate location of the spin axis, and the existence of two jets (one near each pole) (Knight and Schleicher 2009). Later observations were used to constrain the pole solution, and evidence is seen for seasonal effects on the activity of the jets. Periodic comet Tempel 2 was observed extensively during 1999 and 2000. The comet was studied by multiple observers in 1988, and the rotation period was determined to be 8.95 hours (Jewitt and Luu 1989, A'Hearn et al. 1989, etc.). Observations from 1994 indicated that the rotation period had changed since 1988, although the sign of the change was uncertain (Mueller and Ferrin 1996). A change in the rotation period would likely be due to either the spin-up or spin-down of the nucleus due to torques induced by jets. We are in the process of reducing the 1999 data and determining the rotation period via CCD photometry. We hope to determine the sign of the change in rotation period since 1988 and to make predictions for the rotation period prior to its return in 2010.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Wed, 05-Aug-2009
Speaker:   Marc Pound (UMD)
Title:  Special topic: Set up spam filter for department email

Abstract:

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Wed, 12-Aug-2009
Speaker:   Dr. Lucas Paganini (Max Planck Institute)
Title:  Sub-millimeter investigation of the cometary coma using a Monte Carlo model

Abstract: Considered to be unmodified since the formation of the solar system, comets are perfect witnesses of the solar system formation and thus enable us to trace the physical, thermochemical and dynamical conditions of the regions in the solar nebula where cometary material was formed. As a comet approaches the Sun the bulk composition of cometary nuclei can be analyzed by (sub)millimeter spectroscopy. In contrast to shorter wavelengths observations, the analysis of cometary comae by means of this method allows to monitor parent molecules with high spectral resolution. Clearly, a correct interpretation of line intensities and production rates of parent molecules, throughout the whole cometary coma, requires the inclusion of all excitation parameters and radiative transfer in the optical thick case. The ultimate aim of this talk is to present a numerical code which allows the simulation of water molecules in cometary comae and hence facilitates the understanding of the physical conditions observed.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 13-Aug-2009
Speaker:   Alan Gersch (UMD)
Title:  Modeling Spectra of Cometary Comae Including Optical Depth Effects

Abstract: Comets are thought to be frozen remnants from the formation of our solar system. As such, their chemical composition is of great significance to understanding the origin of the planets and the distribution of important molecules, including water, throughout the solar system. This was and is a major goal of the Deep Impact (DI) Mission. The goal of this thesis research is to better understand the abundances, distributions and creation mechanisms of various gases observed by DI in the coma of comet Tempel 1, the target of the DI Mission. In order to do so, we have built a computer model of the spectra of the comet's coma that includes the difficult and often ignored problem of accurately modeling radiative transfer. This model can deal with the possibility of an optically thick coma. This model will facilitate analyzing the actual spectral data from the Deep Impact mission to better determine abundances of key species, including CO, CO2 and H2O.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 10-Sep-2009
Speaker:   Stef McLaughlin, Ludmilla Kolokolova, Lori Feaga, Lucy McFadden, Jian-Yang Li, Nelly Mouawad (UMD)
Title:  Photo Extravaganza

Abstract: Come and enjoy the showing of photos taken from all continents! We will show our travel and family photos from New Zealand, Japan, Iceland, China, Lebanon, and of course, the US.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 17-Sep-2009
Speaker:   Lucy McFadden (UMD)
Title:  A Search for Satellites of Vesta: Upper Limits on Their Size

Abstract: L.A. McFadden, F. Bastien, C. A. Crow, D. P. Hamilton, J-Y Li, M.J. Mutchler, University of Maryland, College Park, MD and Space Telescope Science Institute.

A search for moons of Vesta was conducted using 40 s exposures with Hubble Space Telescope’s Wide Field Planetary Camera 2 on May 14 and 16, 2007. An area extending from 14-260 Vesta radii was searched with no satellites found. Artificial satellites represented by a two-dimensional Gaussian profile were randomly inserted into the images after determining that orbital motion of a detectable satellite would be negligible. Twenty-seven people searched the images for satellites resulting in a 90% confidence level of 0.2 magnitude precision and a variance of 0.77. Artificially implanted satellites were found down to a magnitude of 22.5 ±0.2 by almost all searchers. Assuming any moon would have Vesta's albedo, this magnitude corresponds to an upper limit of 44 ±4 m. Knowing that Vesta has a large basin in its southern hemisphere and that the ejecta from that impact likely produced 3-25 km sized bodies called Vestoids it is interesting that none of the impact debris remained in orbit around Vesta. Satellite formation by cratering is very inefficient and any satellites that might have formed from such an event would have to survive for billions of years. Continued searches are warranted for their scientific interest and in support of the Dawn mission.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 24-Sep-2009
Speaker:   Brian Jackson (GSFC)
Title:  Close-in Extra-Solar Planets and Tides

Abstract: In the last 15 years, astronomers have found almost 400 planets orbiting stars other than our Sun. These extra-solar planets have a remarkable diversity of orbital and physical properties, many unlike planets in our own solar system. Even in this exotic menagerie, close-in extra-solar planets stand out as unusual and puzzling. These planets have masses ranging from several Earth masses to many Jupiter masses, but orbits that are at least 10 times closer to their host stars than the Earth is to the Sun. Because they are the easiest planets to detect, close-in planets provide much of our current information about physical and orbital properties of extra-solar planets, so understanding their mysterious origin and evolution is important for understanding planets in general. Within such proximity to their host stars, close-in planets are especially susceptible to the effects of tides. Tidal deformation of the planets by their host stars and of the host stars by their planets can affect the planets' orbital and thermal evolution. For example, tides can circularize orbits and cause them to decay. In many cases, tides may have already destroyed many close-in planets by causing them to crash into their host stars. As tides change the orbits of these planets, they can also heat their interiors. This heating may cause gaseous planets to become inflated, or may drive vigorous volcanism on rocky planets, as on Jupiter's moon Io. Tides can also help strip the atmospheres from gas giant planets that wander too close to their host stars. In fact, there are indications that the first unambiguously rocky extra-solar planet discovered, CoRoT-7 b, may actually be the remnant rocky core of a tidally stripped gaseous planet. In this talk, I will discuss our rapidly evolving knowledge of close-in extra-solar planets, and highlight the important and complex role played by tides.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 01-Oct-2009
Speaker:   DPS speakers (at request)
Title:  DPS practice talks

Abstract:

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 08-Oct-2009
Speaker:   No talk
Title:  DPS

Abstract:

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 15-Oct-2009
Speaker:   Jessica Sunshine (UMD)
Title:  Water on the Lunar Surface as Observed by M3 and the Deep Impact Spacecraft

Abstract: During its extended mission (EPOXI) the Deep Impact spacecraft has routinely observed the Moon for calibration purposes, particularly for the near infrared spectrometer. Most recently (June 2009) we obtained two long-planned sets of observations, while the spacecraft viewed the northern polar regions. The synoptic perspective of these hemispheric data complements the high spatial resolution data from Moon Mineralogy Mapper (M3) on-board India¹s Chandrayaan-1 spacecraft. In addition, the 1-5 microns Deep Impact spectrometer extends the spectral range beyond M3, which, for example, allows for a more complete measurement and removal of the thermal emissions that affect lunar spectra at wavelengths as short as 2.2 microns. Deep Impact has confirmed the presence of water discovered by M3 (see also Clark, this session) and extended their detection to all latitudes, including low abundances at the equator (seen in prior calibration data from December 2007). In addition, the June 2009 observations include two sets of data separated by one week, during which the Moon rotated 90 degrees (i.e., 1/4 lunar day). These data reveal a dynamic, thermally activated process consistent with the presence of surfical water.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 22-Oct-2009
Speaker:   Chris Stark (GSFC)
Title:  Decoding Debris Disks: Modeling the Dynamical Signatures of Exoplanets

Abstract: Many main sequence stars exhibit an infrared excess that has been interpreted as thermal emission from a circumstellar dust disk, likely created by collisions or outgassing of planetesimals in these disks of debris. Several resolved debris disks show circumstellar ring-like structures likely caused by planetary perturbations. In our own tenuous debris disk, the zodiacal cloud, we see the faint signature of Earth itself, while resolved images of several debris disks much more dense, including Fomalhaut and HR 4796A, exhibit similar structures at much greater circumstellar distances. Until now, no debris disk model has been able to simultaneously include the gravitational resonant dynamics and grain-grain collisions necessary to accurately model these dust disks. I will present the first debris disk models to include all of the necessary physics and describe the modeling techniques we used. I will show our predictions for the structures we may see in future observations which can image structures due to Earth-mass planets, and present the first preliminary 3D collisional simulations of the Fomalhaut debris disk.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 29-Oct-2009
Speaker:   Sebastien Besse (UMD)
Title:  Asteroid (2867) Steins as imaged by the OSIRIS cameras on board Rosetta spacecraft

Abstract: The Rosetta spacecraft has successfully flew by the 5th September of last year the asteroid Steins, first scientific objective of the mission on its way to rendez-vous comet 67P/Churyumov-Gerasimenko in 2014. Different instruments were turn on, especially the two cameras of the OSIRIS experiment. Images at closest approach have a scale of 80 meters per pixel and reveal collisional and dynamical processes of this small size asteroid. The mean radius is 2.7 km with a flat south pole shape dominated by the largest impact on the observed surface. The shape of the two hemispheres separated by an elevated equator may be the first direct observation of the YORP effect on a small body. The observed surface present 42 craters ranging from 150m to 2100m with a mean depth-to-diameter ratio of 0.12. This low ratio compare to previous small bodies may be the combination of severals mechanism included surface erasure by the large impact at the south pole. Finally, the age of asteroid Steins is 154 Myr based on Nolan's law. The young age of the surface and shallowed craters are arguments in favor of the resurfacing of the surface by the large impact that could have occurred 32 Myr ago.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Mon, 02-Nov-2009
Speaker:   Dr. Murthy Gudipati (UMD/IPST, JPL)
Title:  Chemical Physics of Solar System Ices

Abstract: The formation of a star from a protoplanetary disk, the evolution of a solar system consisting of planets, satellites, and small bodies - all this is a part of the cyclic process of birth and death of a star in a galaxy. Majority of the space in the galaxy and in the solar systems is filled with very cold material, most of which is in the form of ice. The farther are the objects from the star, the cooler are their temperatures. After H2, H2O is the most abundant molecule in the universe. Thus, both in the interstellar space and in our own solar system, majority of bodies are comprised of cold icy surfaces and interiors. Evolution of these icy bodies is an integral part of the evolution of our solar system.

Water ice is a highly complex solid, with unique physical and chemical properties. Water ice coexists with mineral grains in many surroundings. Organics are typically found to be embedded as impurities in the icy surfaces. Water ice has the highest sublimation/melting point among the most abundant molecular ices in the universe. Consequently, water ice is found at a wide temperature range, from < 10 K to 160 K under little or no atmosphere, up to 273 K under atmosphere, and even higher under very high pressures. Density of ice can vary from as low as 0.2 g cm-3 in certain amorphous phases to above 2.5 g cm-3 at very high pressures.

Most of the solar system surfaces are subjected to constant particle and photon bombardment, which induces energetic processing of these ices and triggers complex chemistry. In the presence of organic (C, H, and N containing molecules) impurities, this leads to the formation of biologically relevant molecules. One of the working hypotheses for the origin of life is that early comet bombardment of earth brought water and biological molecules to the earth.

From the above narration, the role of chemical physics (physics and chemistry) in understanding the formation and evolution of icy objects in the universe is clearly evident. In our laboratory we have been conducting research on cryogenic ices with the aim of translating their properties into the evolution of icy bodies in our solar system and in the universe.

The talk will give a general overview, discuss some specific laboratory investigations involving radiation, organics, and ices, and infer the relevance of these studies to the evolution of ices in our solar system.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 05-Nov-2009
Speaker:   Max Mutchler (STSci)
Title:  Hubble's expanded capabilities following the Servicing Mission

Abstract: The fifth Hubble Servicing Mission was conducted by Space Shuttle Atlantis in May 2009. Following months of orbital verification and calibrations, HST is back in business with greatly expanded capabilities. Max Mutchler supported the repair of the Advanced Camera for Surveys (ACS) and subsequent calibrations, and also the Early Release Observations (ERO) for both ACS and the newly-installed Wide Field Camera 3 (WFC3). He will share his knowledge of the early performance of Hubble's cameras, with particular insights for scientists considering proposing for the "new" HST.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 12-Nov-2009
Speaker:   Valeria Cottini (GSFC)
Title:  Infrared space-borne spectroscopy of Mars and Venus: Atmospheric Composition from Mars Express and Venus Express data

Abstract: The atmospheric composition of Mars and Venus and the retrieval of the abundance of its relevant minor gases can be achieved by the use of infrared space-borne spectroscopy and analisys of the outcoming radiation from the planet atmosphere and the comparison of these data with models, computed by use of radiative transfer, which reproduce the physical properties of the atmosphere. In this seminar I'm going to present some results on the search for minor species in the Martian and Venusian atmosphere with an important impact on the global knowledge of dynamics, physical process and evolution of the atmosphere.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 19-Nov-2009
Speaker:   Doug Hamilton (UMD)
Title:  Saturn's Largest Ring

Abstract: Saturn's largest ring encompasses the orbits of the planet's three dozen known irregular satellites. These moons follow highly eccentric and inclined orbits that loop around the planet at large distances. Roughly three quarters of them have retrograde orbits, circling the planet in a direction opposite the inner satellites. Phoebe, with a radius of 107km, dominates this population. The largest of the prograde satellites, most of which have orbits inclined by 30-50 degrees, is 20km Siarnaq. Numerous past collisions amongst satellites as well amongst the larger debris from the satellites is likely responsible for the generation of the new ring.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 26-Nov-2009
Speaker:   No talk
Title:  THANKSGIVING!

Abstract:

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 03-Dec-2009
Speaker:   Avi Mandell (GSFC)
Title:  Exploring Gas Chemistry in Exo-Planet Atmospheres and Protoplanetary Disks

Abstract: Characterizing the gas chemistry in the atmospheres of "Hot Jupiters" and the planet-forming regions of young circumstellar disks is essential to understanding the evolution of planetary systems and preparing for observations of Earth-like planets. Near-infrared spectroscopy (1 - 5 µm) provides a unique window into molecular chemistry occurring in irradiated planetary and protoplanetary environments. The spectral range covers both low-energy and high-energy ro-vibrational transitions for a large variety of simple oxygen- and carbon-bearing molecules tracing a rich network of chemical reactions, and the spectral and spatial resolution at these wavelengths allows accurate measurements of the thermal and kinematic structure of warm (500K - 1500K) gas in environments such as the warm subsurface molecular layers of young circumstellar disks and the outer atmospheres of hot extra-solar planets. In this talk, I will discuss ongoing campaigns to trace the water and organic chemistry in these environments using high-resolution spectrographs on the Keck and VLT telescopes with unprecedented precision. Our results on circumstellar disks yield detailed information on the radial and vertical structure of the inner 10 AU of planet-forming disks, and our exo-planet observations may provide the first high-resolution spectrum of an exo-planet from the ground.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


Date:   Thu, 10-Dec-2009
Speaker:   Nick Moskovitz (DTM)
Title:  Characterization of Vesta-like Asteroids: Constraints on the earliest stages of planet formation

Abstract: Asteroids with surfaces composed of basaltic material are interpreted as collisional fragments derived from the crusts of differentiated planetesimals. Until recently, the only known example of such objects were the Vestoids, a collisional family of asteroids dynamically linked to 4 Vesta. However, new discoveries have revealed non-Vestoid basaltic asteroids throughout the Main Belt. I will present our current understanding of the number, orbital distribution and mineralogy of these relatively rare objects. These results will be used to highlight a long outstanding problem related to the process of differentiation, namely the scarcity of basaltic crustal material relative to metallic core fragments amongst both asteroid and meteorite populations. Several physical mechanisms will be discussed as possible causes of this discrepancy.

For further information please contact PALS coordinator Dr. Jian-Yang Li at jyli@astro.umd.edu, 301-405-2103.


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