List of Past Planetary Astronomy Lunches (PALS) : 01-Jan-2009 to 01-Jun-2009


Date:   Thu, 08-Jan-2009
Speaker:   Dr. Richard Walker (UMD)
Title:  Highly Siderophile Elements in the Earth, Moon and Mars: Implications for Planetary Accretion and Differentiation

Abstract: The highly siderophile elements (HSE: Os, Ir, Ru, Pt, Pd, Au) pose a challenge for planetary geochemistry. As highly siderophile (iron-loving) elements, they are normally strongly partitioned into metal relative to silicate. Consequently, planetary core segregation might be expected to essentially quantitatively remove these elements from planetary mantles. Yet, the abundances of these elements estimated for Earth's primitive upper mantle (PUM) and the martian mantle are broadly similar, and only about 200 times lower than chondritic meteorites. In contrast, although problematic to estimate, abundances in the lunar mantle may be more than twenty times lower than in the terrestrial PUM. The generally chondritic Os isotopic compositions estimated for the terrestrial, lunar and Martian mantles require that their long-term Re/Os ratios were also within the range of chondritic meteorites. Further, most HSE in the terrestrial PUM appear to be present in chondritic relative abundances.

Numerous hypotheses have been proposed to account for the HSE present in Earth's mantle. These hypotheses include inefficient core formation, decreased siderophilic behavior resulting from metal segregation at elevated temperatures and pressures (as may occur at the base of a deep magma ocean), and late accretion of materials with chondritic bulk compositions after the cessation of core segregation. Participation of aspects of each of these processes may not be surprising, as it is difficult to envision the growth of a planet, like Earth, without the involvement of each.

For further information please contact PALS coordinator Dr. Nelly Mouawad at mouawad@astro.umd.edu, 301-405-0791.


Date:   Thu, 15-Jan-2009
Speaker:   Dr. Conor Nixon (GSFC)
Title:  Titan's Chemical Cornucopia from Cassini

Abstract: Titan is the only moon in the solar system with a substantial atmosphere, which is composed mainly of nitrogen (N2) like that of the Earth, but with a significant minority of methane (CH4, 2-6%). Beginning in the upper atmosphere, charged particle impacts and solar UV photons dissociate these raw materials into reactive radicals and ions, which recombine forming a plethora of more complex CHN molecules, including saturated and unsaturated hydrocarbons, nitriles and amines. An external influx of water, apparently originating from the active moon Enceladus, provides oxygen to form CO and CO2.

The Cassini spacecraft, now entering its fifth year of operations in Saturn orbit, has made more than 45 close flybys of Titan. Its many instruments are returning a wealth of data regarding the moon, from the interior to the ionosphere, and helping to answer many long-standing questions. In this seminar I will focus on the results pertaining to the atmospheric composition, especially the global mapping of stratospheric compounds by Cassini's Infrared Spectrometer (CIRS) that I have been most involved with. I will discuss how the CIRS results, combined with those from the mass spectrometer and other instruments, are changing our view of Titan, which has now emerged as a major focus for astrobiological investigation.

For further information please contact PALS coordinator Dr. Nelly Mouawad at mouawad@astro.umd.edu, 301-405-0791.


Date:   Thu, 29-Jan-2009
Speaker:   Dr. Dennis Bodewits (GSFC)
Title:  Remote observation of the interaction between comets and the solar wind: Cometary X-ray and EUV emission

Abstract: The interaction of the solar wind with the planets and the interstellar medium is of key importance for the evolution of our solar system. The interaction with Earth's atmosphere is best known for the northern light. In case of Mars, the interaction with the solar wind might have lead to the erosion of its atmosphere.

Solar wind-atmosphere interactions can be studied particularly well in cometary atmospheres, because in that case the solar wind flow is not attenuated by a planetary magnetic field and interacts directly with its atmosphere, the coma. The size of the cometary atmosphere (in the order of 104 - 105 km) allows remote tracking of the ions as they penetrate into the comet's atmosphere, offering a unique window on the cometary atmosphere, the solar wind and the interaction of these two plasmas.

When solar wind ions fly through an atmosphere they are neutralized via charge exchange reactions with the neutral gaseous species. These reactions depend strongly on target species and collision velocity. The resulting X-ray and Far-UV emission can therefore be regarded as a fingerprint of the underlying reaction, with many diagnostic qualities.

For further information please contact PALS coordinator Dr. Nelly Mouawad at mouawad@astro.umd.edu, 301-405-0791.


Date:   Thu, 05-Feb-2009
Speaker:   No talk
Title:  DIXI Science mtg

Abstract:

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


Date:   Thu, 12-Feb-2009
Speaker:   Mike Kelley (UMD)
Title:  The (Refractory) Stuff Comets Are Made Of

Abstract: Comets are reservoirs of pristine material found in the early outer-solar system. Refractory grains buried in comet interiors have likely remained unchanged since they were incorporated into comet nuclei 4.6 Gyr ago. What is the composition of that material? Is it pre-solar, processed by the proto-planetary disk, or a mixture of the two? Mid-infrared spectra of comet comae are well-suited for assessing the bulk composition of comet dust. The Spitzer Space Telescope and mid-infrared instrumentation on 8 meter class ground-based telescopes are providing us with the spectra we need to understand the origin of comet dust. In this talk, I will present the evidence for large scale mixing and processing of refractory material in the early solar system, and present results from a spectroscopic survey of comets with Spitzer that has more than doubled the number of mid-IR spectra of comet comae. I will also discuss how spectra of comets are helping us test theories of water variability in the early inner-solar system and dynamical models of the formation of the Oort Cloud and Scattered Disk.

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


Date:   Thu, 19-Feb-2009
Speaker:   Carlos A. Romero Talamas (UMD)
Title:  Plasma experiments at the Institute for Research in Electronics and Applied Physics: MCX and the Space Weather Simulator

Abstract: Plans for an existing facility, the Maryland Centrifugal Experiment (MCX), and a future facility, the Space Weather Simulator, will be discussed. The MCX facility has been operating at the Institute for Research in Electronics and Applied Physics (IREAP) for several years now, and is aimed at exploring the feasibility of using centrifugally confined plasmas to produce controlled thermonuclear fusion energy. The Space Weather Simulator is a desired facility in the very early stages of planning, which will be used to study a wide range of topics, including magnetic reconnection and magnetic topology evolution, the Sun-Earth connection, and the effects of energetic particles and radiation on electronic components, among others. Present and future diagnostics, as well as the possibility for establishing collaborations and expanding research interests, will also be discussed.

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


Date:   Thu, 26-Feb-2009
Speaker:   Hannah Jang-Condell (UMD)
Title:  Catching Planet Formation in the Act: Connecting Protoplanetary Disk Theory to Observations

Abstract: Over 300 exoplanets have been discovered to date, with orbital parameters entirely unlike our our Solar System. The question of how these planetary systems arise must be studied in the context of how planets interact with the circumstellar disks from which they form. In turn, planet formation theory must be studied in conjunction with observations of circumstellar disks. I examine two applications of connecting protoplanetary disk theory to observations: planet formation in close binary systems, and identification of signatures of planet formation in circumstellar disks.

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


Date:   Thu, 05-Mar-2009
Speaker:   Rob Olling (UMD)
Title:  Astrometric & Photometric Detection & Characterization of (massive) Extrasolar Giant Planets

Abstract:

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


Date:   Thu, 12-Mar-2009
Speaker:   Todd Smith (JHUAPL)
Title:  Atmospheric probing with Cassini energetic neutral imaging to investigate the mysterious Titan

Abstract: Saturn's largest moon, Titan, provides an interesting opportunity to study how dense atmospheres interact with the surrounding plasma environment. Without an intrinsic magnetic field, this satellite's nitrogen-rich atmosphere is relatively unprotected from plasma interactions and should produce co-orbiting neutral nitrogen particle clouds. However, these clouds have not been detected so it is important to more closely examine how this moon interacts with its environment and loses atmosphere. Atmospheric energy deposition rates are a key component to these processes and for understanding chemistry and dynamics in Titan's atmosphere. The NASA Cassini mission has been conducting in situ investigations of Titan for over four years and is providing ground breaking observation of this region. However, Cassini never passes closer than ~ 960 km to Titan's surface so we use the Cassini MIMI Ion-Neutral Camera (INCA) to remotely image energetic hydrogen particle fluxes at altitudes below Titan closest approach where in situ observations are not possible. These results along with computational modeling provide insight into this unique planetary satellite.

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


Date:   Wed, 18-Mar-2009 [Date Change!]
Speaker:  
Title:  LPSC practice talks

Abstract:

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


Date:   Thu, 26-Mar-2009
Speaker:   No talk
Title:  LPSC

Abstract:

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


Date:   Thu, 02-Apr-2009
Speaker:   Marc Kuchner (GSFC)
Title:  Measuring Sizes and Shapes of Dwarf Planets and Centaurs with SIM

Abstract: The discovery of the large size of Eris, a Kuiper belt object, recently led to Pluto's controversial demotion to the status of dwarf planet. But the sizes of most dwarf planets are only know to typically 20%! I will describe a proposed new program that uses the Space Interferometry Mission (SIM) to measure the sizes of KBOs, Centaurs, and asteroids to much higher accuracy. SIM can also allow us to tomographically reconstruct the shapes and rotation axes of these bodies and constrain their surface homogeneity, density, and other fundamental properties inaccessible to any other method (except visiting them with a probe).

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


Date:   Thu, 09-Apr-2009
Speaker:   Carey Lisse (JHUAPL)
Title:  Comparing Enceladus to Comets: Implications for Enceladus' Activity

Abstract: Despite obvious physical differences in size, shape, and surface albedo between Enceladus and cometary nuclei, the compositional similarities between the vented gases from Enceladus and the gases in cometary comae are striking. The approximately 1028 molecules/sec of material emitted from Enceladus, composed mostly of water with some hypervolatile species, flows out in jets similar to those seen for moderately active comets. Using recent data from Cassini instruments, including the Ion and Neutral Mass Spectrometer (INMS), the Visual and Infrared Mapping Spectrometer (VIMS) and the Imaging Science Subsystem (ISS), we investigate the compositional similarities between Enceladus' plumes and cometary comae and we compare the physical properties (densities, speeds, collimation) of the plumes and cometary jets. We will discuss the implications our findings have for various aspects of the origin and evolution of Enceladus.

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


Date:   Thu, 16-Apr-2009
Speaker:   Geronimo Villanueva (GSFC)
Title:  Is Mars Alive?

Abstract: Methane, a biomarker on Earth, is present on Mars. We discovered strong release of methane from three regions on Mars during Northern summer in 2003. This discovery demonstrated the existence of windows into the planet's geochemical and/or biological processes, and stimulated keen interest in the origin of the methane released.

Is methane on Mars related to biology? When was this gas produced? The answer may lay in the infrared, since multiple key bio/geochemical species on Mars have strong signatures at these wavelengths. In this talk, we will present our latest results of our 10-years observational campaign of multiple biomarkers on Mars, including measurements of isotopic deuterated water, a chronometer testing the age and origin of volatiles on Mars.

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


Date:   Thu, 23-Apr-2009
Speaker:   Alan Gersch (UMD)
Title:  

Abstract:

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


Date:   Thu, 30-Apr-2009
Speaker:   Larry Nittler (CIW/DTM)
Title:  Comet Dust in the Laboratory

Abstract: Comets are among the most primitive bodies in the Solar System and hence provide useful information about the starting materials and early evolution of the Solar System. Dust particles from Jupiter-family cometWild-2 (W2) were collected and returned to Earth by NASA's Stardust mission in 2006. In addition, tiny meteorites (interplanetary dust particles, or IDPs) are collected at high altitude in Earth's stratosphere, and a significant fraction of these are believed to originate in comets. In 2003, a special IDP collection was timed to maximize the chances of collecting dust from a specific Earth-crossing comet, Grigg-Skjellerup (GS). Laboratory studies of cometary dust provide complementary information to astronomical observations for better understanding comets. Recent investigations have indicated a remarkable diversity in the mineralogical, chemical and isotopic compositions of cometary dust on a variety of scales. This talk will review some of the more exciting recent results in comet dust research.

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


Date:   Thu, 07-May-2009
Speaker:   Sylvio Ferraz Mello (University of Sao Paulo, Brazil)
Title:  Tidal evolution of close-in satellites and exoplanets

Abstract: Our knowledge of tidal friction is even today directly founded on Darwin's theory. Many progresses from studies done in the past century deserve mention. To quote just a few, we may mention Love?s theory on the elastic response of one body submitted to an external potential and the understanding of the role played by tides in generating heat in synchronous planetary satellites. We may also mention the many applications that leaded to the understanding of the evolution of systems with close-in satellites, the Earth-Moon system in the first place. However, notwithstanding the existence of some high-order formal theories, the essential of our knowledge is yet nowadays the one established by Darwin and crucial questions on the action of viscosity, for instance, remains unanswered. I intend to critically review our current understanding of Darwin's theory and several problems concerning the tidal evolution of Titan, which may be considered as deserving attention.

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


Date:   Thu, 14-May-2009
Speaker:   Derek Richardson (UMD)
Title:  Testing Cohesion in Gravitational Aggregates

Abstract: New observations of small asteroids support the idea that many small solar system bodies are gravitational aggregates of loosely bound material. Recent evidence includes a morphological match between radar-derived models of near-Earth asteroid binary 1999 KW4 and theoretical models based on thermal (YORP) spinup of rubble piles (Walsh et al. 2008, Nature 454, 188). Rubble piles are gravitational aggregates with zero cohesion (no tensile strength). The effect of a small amount of cohesion (< 100 Pa, an approximate upper limit based on observations of comets D/Shoemaker Levy 9 and P/Tempel 1) is only just beginning to be explored in numerical simulations. Given that some small solar system bodies have spins in excess of theoretical limits for unconsolidated material, there is motivation to model weak cohesion in these bodies.

We have developed a simple model of weak cohesion based on a Hooke's-law-type restoring force (springs) between adjacent spherical particles in an idealized rubble pile. The "springs" are characterized by the Young's modulus (which determines spring strength) and stress limit (maximum distension before breaking). Once a spring breaks, it remains broken. The particles essentially act as tracers of a continuum solid that deforms under stress until failure.

To explore this model, we have conducted a series of stress tests in which assemblages of particles are subjected to increasing tensile or shear stress until failure. We find that these bodies fail near the center for slowly applied stress, and at multiple locations for rapidly applied stress, reminiscent of real materials. We use these tests to determine an overall bulk strength of the material as a function of packing geometry, "spring" parameters, number of particles, etc., for comparison with real materials and analytical models. We have begun to include cohesion in simulations of rotational disruption of gravitational aggregates and will report on preliminary results.

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


Date:   Thu, 18-Jun-2009
Speaker:   Lori Feaga (UMD)
Title:  Characterizing Steins from Rosetta Alice UV Data

Abstract: During Rosetta.s flyby of the main-belt, E-type asteroid (2867) Steins on 5 Sept. 2008, the U.S. Alice UV imaging spectrometer was used to obtain the first far-ultraviolet (FUV) spectrum of an asteroid. A ten minute integration, averaging over a variety of geometries at closest approach, shows very good signal from 850 to 2000 representing the first spectrum of an E-type asteroid below the atmospheric cutoff. We find that the far ultraviolet albedo of Steins is very low, ~5%, compared to its visible albedo, 41% (Keller et al. 2009; Weissman et al. 2008; Jorda et al. 2008), as is expected from the UV behavior of many refractory materials. We also find that the albedo does not show a dramatic color variation over the FUV spectral range; however, there is a pronounced dip near 1600 . In addition, Alice obtained the total FUV count rate integrated with 1 second resolution during the encounter to determine the average variation of reflected UV flux with phase angle. In comparison to the OSIRIS WAC data, Alice data show clear wavelength dependent phase reddening and that the opposition effect is greater in the FUV than in the visible.

In addition to observing Steins at closest approach, a ~22 hour exosphere search was conducted prior to closest approach with Steins in the Alice slit. As expected from the only existing model (Schlppi et al. 2008), a deep search for any exosphere (e.g., hydrogen, oxygen) yielded no obvious detections in our initial analysis. We have placed upper limits on an atomic hydrogen and oxygen exosphere at Steins.

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


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