List of Past Planetary Astronomy Lunches (PALS) : 01-Sep-2008 to 31-Dec-2008


Date:   Thu, 04-Sep-2008
Speaker:   Dr. Carey Lisse (JHU-APL)
Title:  Dusty Disks & Comets: Clues to the Formation and Evolution of the Solar System

Abstract: With the Spitzer Space Telescope (SST) we are for the first time beginning to understand the details of how the composition and formation of our own Solar System compares to those of other stars in our Galaxy. This is a major question in astronomy, and recent, detailed observations by SST of comets (remnants of the solar systems proto-stellar nebula), protoplanetary disks around young stellar objects (YSOs), and debris disks around moderate-age stars have given us a collection of detailed spectra containing clues about our Galactic context. In this talk I will discuss these observations, which are comprised mainly of mid-infrared (5 to 40 micron) spectroscopy of dust grains and gas. Using the results from the recent Deep Impact and STARDUST space missions, we can now constrain the relative abundances of silicates, carbonates, water ice, amorphous carbon, sulfides, and polycyclic aromatic hydrocarbons (PAHs) in these environments. I will discuss the similarities and differences in the spectra, and their implications to larger questions of our Solar System's origins.

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


Date:   Thu, 11-Sep-2008
Speaker:   Dr. Natalia Gomez (Carnegie Instution of Washington)
Title:  Planetary Dynamos in the Solar System

Abstract: The intrinsic magnetic field of Earth is known to be generated at the planetary core by a process called geodynamo. In many cases, planetary bodies through out the solar system have been found to have intrinsic magnetic fields. They may be generated by dynamo processes, similarly to Earth, but their geometry and temporal behavior may differ significantly among them. >From the solar dynamo to the magnetic field of the ice giants, I will try to illustrate how numerical models can contribute to the understanding of the internal planetary dynamics based on the observed intrinsic magnetic fields.

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


Date:   Thu, 18-Sep-2008
Speaker:  
Title:  

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


Date:   Thu, 25-Sep-2008
Speaker:   Dr. Tom Statler (Department of Physics and Astronomy, Ohio University)
Title:  The Spin States of Small Near-Earth Asteroids

Abstract: Large asteroids, with diameters of 150 meters or larger, have rotation periods longer than 2 hours, corresponding to the spin limit for gravitationally bound "rubble piles." Small asteroids, on the other hand, do not. A population of fast-rotating objects is seen among the near-Earth asteroids (NEAs) smaller than 150 m. Neither the source, nor the implications, of this rapid rotation are clear. Torques produced by the radiation-recoil (YORP) effect modify the spin rates and obliquities on timescales of 10^6 to 10^7 years, which coincide with the objects' typical lifetimes. Neither the actual spin rate distribution nor the obliquity distribution is known, because of the obvious difficulties in observing asteroids the size of office buildings at multi-megamile distances. In this talk, I will report on preliminary results from observations of ~ 40 NEAs with diameters between 20 and 500 meters, showing that the actual spin rate distribution for the smallest objects is quite different from what previously published data implies. I will discuss the implications of these results for the evolution of asteroid spins and possible constraints on material strength.

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


Date:   Thu, 02-Oct-2008
Speaker:   Dr. Matt Burger, UM
Title:  No Sodium in the Enceladus Plume: Implications for a Sub-Surface Ocean

Abstract: One surprising discovery of the Cassini mission to Saturn has been the presence of geyser-like plumes at the south pole of the icy moon Enceladus ejecting >300 kg/s of water into Saturn's magnetosphere. In situ and remote observations (Waite et al. 2006; Hansen et al. 2006) have shown that the primary plume constituent is H2O, and thermal measurements indicate intense heating in cracks believed to be plume vents on the surface (Spencer et al. 2006). These observations have led to speculation that the plumes are fed from a liquid water reservoir beneath Enceladus' surface.

I present results from an extremely sensitive, high-resolution spectroscopic search using the Keck and Anglo-Australian Telescopes which place a stringent upper limit on sodium emission in the Enceladus plumes. Large amounts of sodium would be expected if Enceladus' plume material were derived directly from a subsurface liquid reservoir in contact with rocky material. Chemical models predict that sodium would dissolve into such an ocean at mixing ratios relative to water of 10-4 to 10-1 (Zolotov et al., 2007). Numerical plume models show that such high sodium concentrations would form a detectable torus encircling Saturn. The detection upper limits for sodium in both plume and neutral torus fall orders of magnitude below these models, leading us to conclude that the Enceladus plumes do not originate in an ocean or sea. These observations support the alternative theories that the plumes are generated by shear heating of the icy crust resulting in sublimation or melting, or the decomposition of clathrates.

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


Date:   Thu, 09-Oct-2008
Speaker:  
Title:  DPS Practice talks

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


Date:   Thu, 23-Oct-2008
Speaker:  
Title:  

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


Date:   Thu, 30-Oct-2008
Speaker:   Dr. Tim Livengood (NASA/GSFC)
Title:  Earth as an Earth-like Planet

Abstract: The re-purposed Deep Impact spacecraft was used as part of the EPOXI mission-of-opportunity to observe the whole disc of the Earth at 57░ phase angle (77% illumination) and 0.18 AU range and at 77░ phase angle (62% illumination) and 0.34 AU range on March 19 and June 5, 2008 (respectively), over a range of wavelength from 350 nm to 4.8 Ám. These observations sample the Earth's optical properties at the seasonal extremes of an equinox and near-solstice. A third observation was obtained on May 29, including a transit of the Earth by the Moon. These measurements constitute an empirical test of proposed methods for the remote characterization of terrestrial planets in extrasolar planetary systems. The visible-light signal was sampled with 7 filters of approximately 100 nm width at 100 nm spacing over 350\u2013950 nm central wavelength, at 15-minute intervals in 4 selected filters and 1-hour intervals in the remaining 3 filters. Near-IR spectroscopy at 1\u20134.8 Ám was obtained at 2-hour intervals. These data provide a rotationally-averaged optical/IR spectrum of the Earth in a typical presentation at low-to-moderate spectral resolution, and light curves of the Earth reflecting the surface distribution of clouds and terrain. Infrared spectroscopy demonstrates the signatures of H2O, CO2, and other telluric species. The visible light curve demonstrates significant time-variability of the optical spectrum associated with terrestrial terrain types. Of greatest significance to proposed extrasolar terrestrial planet characterization, these data provide a test for the suitability of the "Red Edge" as a signature for the presence of chlorophyllaceous life on an unresolved planetary body.

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


Date:   Thu, 06-Nov-2008
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, 13-Nov-2008
Speaker:   Dr. Timothy Stubbs (GSFC)
Title:  The Interaction of the Space Plasma Environment with the Surface of the Moon

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


Date:   Thu, 20-Nov-2008
Speaker:   Yana Radeva (UMD/GSFC)
Title:  The Depleted Organic Composition of Comet C/2000 WM1 (LINEAR) Revealed at Infrared Wavelengths and Searching for Heterogeneity in the Cometary Nucleus

Abstract: The chemical diversity of comets holds the key to understanding how the Solar System formed and evolved. Our team studies comets at infrared wavelengths, which allows us to measure their parent volatile composition (through ro-vibrational transitions of the parent species). The Oort cloud comet C/2000 WM1 (LINEAR) was observed with the Near Infrared Echelle Spectrograph on the Keck II telescope on 23-25 Nov. 2001. I will present the extracted rotational temperatures and production rates for the detected parent volatiles. I will also present the relative production rates (mixing ratios) indicate that WM1 is moderately depleted in HCN, CH4 and CH3OH and significantly depleted in C2H2 and CO. The mixing ratios agree for the three dates, which does not support heterogeneity of this comet's nucleus.

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


Date:   Thu, 04-Dec-2008
Speaker:   **No PALS**
Title:  (PDS Review)

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


Date:   Thu, 11-Dec-2008
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, 18-Dec-2008
Speaker:   Dr. Frederic Merlin
Title:  Surface properties of TNOs and Centaurs from visible and near infrared spectroscopy

Abstract : Small icy bodies of the solar system are numerous and have very different dynamical, physical and chemical properties. Among these objects we find the Transneptunian Objects (TNO) and Centaurs. Centaurs orbit between Jupiter and Saturn while TNOs orbit, most of the time, beyond Neptune. These objects are mainly composed of ices but their chemical properties are not well known.

I observed these far and usually dark objects with the 8 meter class telescopes of the VLT, located on Cerro Paranal, Chile. I used photometry and spectroscopy techniques in the visible and in the near infrared. Visible slopes can be very steep, suggesting the presence of organic compounds. Spectral variety among these objects suggests different chemical composition and irradiation levels from space weathering. In the near infrared, absorption features are relative to volatile species as water, methane, ammonia or nitrogen. Radiative transfer theories and laboratory data allow deep investigation of the surface and give some constraints, as surface temperature, physical state or icy dilution.

I will present some results on these topics, as those obtained among the darkest and smallest TNOs in order to better constrain the scenario that play a role in their evolution processes. I will also present a portrait of the biggest ones, Humea and Eris, where I found accurate details on their physical and chemical properties.

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


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