List of Past Planetary Astronomy Lunches (PALS) : 01-Jan-2012 to 01-Jun-2012


Date:   Thu, 05-January-2012
Speaker:   Andy Cheng (APL)
Title:  Topics in Comet Surface Morphology and Evolution

Abstract: I will discuss two topics pertaining to recent comet encounters by the Deep Impact and Epoxi missions. First I will discuss images of the Deep Impact mission impact site and will argue that the apparent absence of an obvious new crater can be explained if the spacecraft struck a positive relief feature, a block or pinnacle, which is tentatively identified in the pre-impact image. The inferred surface strength in this interpretation is consistent with the higher values ~ 1kPa previously reported. Second, I will discuss the question of whether the markedly different surface morphologies seen at Wild 2, Tempel 1, and Hartley 2 represent an evolutionary sequence or different outcomes of competing geologic processes. I will argue that comets must be considered as geologically active, and that this activity is driven by the cometary activity which responsible for gas and dust production. One manifestation of such activity has previously been discussed, production of fluidized flows, and I will discuss another, which is wind-driven erosion of the surface.

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Wed, 18-January-2012 (Change in regular day !!)
Speaker:   Bin Yang (HAWAI)
Title:  Searching for Water in the Main Belt Comets

Abstract: Main belt comets (MBCs) are a class of newly discovered objects that are dynamically indistinguishable from ordinary main belt asteroids yet exhibit comet-like appearances. The activity of MBCs is believed to be driven by the sublimation of exposed surface ice. The MBCs represent the closest and the third established reservoir of comets (after the Oort cloud and the Kuiper belt). They may have been an important source of water for the Earth's oceans.

I will talk about the two most recently discovered comet-like objects in the main belt. Asteroid (596) Scheila was reported to exhibit a cometary appearance and an increase in brightness in early December 2010. We obtained near infrared and optical spectra of Scheila using the Keck and Subaru telescopes. Comet P/2010 R2 (La Sagra) showed an antisolar dust tail from August 2010 through February 2011. Its brightness increased more than 1 magnitude between August 2010 and December 2010, suggesting on-going dust production over this period. We observed La Sagra using the University of Hawaii 2.2 m, Gemini-North, and Keck I telescopes on Mauna Kea. I will present our observational results and discuss possible mechanisms that could produce the observed activity.

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thur, 02-February-2012
Speaker:   Susan Benecchi (Carnegie)
Title:  Colors and Lightcurves of KBOs

Abstract: The Kuiper Belt population in the outer solar system hosts remnants from the various phases of planet formation from the protoplanetary disk. Their physical properties are a function of their formation and subsequent migration and evolution. I will give a brief overview of our current understanding of the dynamical groups in the Kuiper Belt followed by results from a variety of HST programs to study the colors, variability and binarity of a subset of these objects in both optical and infrared wavelenghts. I will then discuss our follow-up efforts to better characterize the lightcurves of these and other KBOs using the Magellan and Dupont telescopes at Las Campanas Observatory.

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thu, 09-February-2012
Speaker:   Uwe Keller (IGEP, Germany)
Title:  Asteroid 4 Vesta a Dwarf Planet?

Abstract: The Dawn Mission arrived at its first target and currently orbits 4 Vesta. The images corraborate the existence of an impact structure at the south pole, big enough to excavate and eject the Vestoids (Vesta Family). Spectrophotomety of the surface confirms the compositional relation to the HED (Howardites-Eurcrites-Diogenite) meteorites. Measurements of the higher moments of the gravitational field reveal the formation of a substantial iron core. The findings are consistent with Vesta's accretion into a differentiated proto planet at the beginning of the solar system formation (HED age determination).

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thu, 16-February-2012
Speaker:   Dave Blewett (APL)
Title:  Unusual Surface Features and Possible Recent Geological Activity on Mercury

Abstract: Flyby observations of the planet Mercury by Mariner 10 and MESSENGER showed that some impact craters contain unusual high-reflectance patches that have relatively flat ('blue') reflectance spectra at visible to near-infrared wavelengths. High-resolution images returned by MESSENGER since the spacecraft began orbiting Mercury in March 2011 reveal that the high-reflectance, blue areas consist of shallow, irregular, rounded depressions with flat floors and bright interiors and halos. These features have come to be called 'hollows'. I will describe the morphologic and spectral characteristics of these fascinating features, present rough constraints on their ages and the rate at which they may be forming, and relate some of the hypotheses for formation of hollows that are being debated within the MESSENGER team.

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thu, 23-February-2012
Speaker:   No Speaker
Title:  no Talk

Abstract: No Talk

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thu, 01-March-2012
Speaker:   Yunzhao Wu (Nanjing University, China)
Title:  Deep Space Exploration in China

Abstract: As the new member of the deep space exploration family, China has and will make policy and program to quickly develop its deep space exploration. My talk will contain three major parts: 1) the outline of China's deep space exploration; 2) some results from Chang'E-1 and -2 mission; 3) I will focus on one of important payload onboard Chang'E-1, the Interference Imaging Spectrometer (IIM). I will show its calibration, flat-field correction, photometric normalization, comparison with M3 data, and global major elements and Mg# derived from this payload.

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thu, 08-March-2012
Speaker:   Wes Patterson (APL)
Title:  New views of Europa

Abstract: Jupiter's Galilean moon Europa is a planet-sized body that, at face value, appears completely foreign in form and process. However, conditions within the satellite are such that we draw analogy with Earth's biologically rich sea floor. Consequently, Europa is a prime candidate in the search for present-day habitability and life in the solar system. Understanding the details of the processes that shape Europa's ice shell, and the exchange processes between its surface and interior ocean, are key to understanding the satellite's potential habitability. In this talk, I will discuss several recent insights into these processes and describe how they provide a new, and strangely familiar, view of this seemingly foreign moon. I will also discuss the future of Europa as a destination for exploration and the challenges ahead in getting there.

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thu, 15-March-2012
Speaker:   J-Y. Li, S. Schwartz (UMD)
Title:  LPSC Practice

Abstract: Bright materials on Vesta and Simulating Low-Speed Rubble Pile Collisions

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thu, 22-March-2012
Speaker:   NO PALS
Title:  LPSC conference

Abstract: TBP

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thu, 29-March-2012
Speaker:   Jean-Baptiste Vincent (MPS, Germany)
Title:  Numerical modelling of dust coma structures

Abstract: One of the key questions we want to investigate on comets concerns the activity of the nucleus. It has been known for decades that this process is driven by solar illumination, sublimating the ice present at the surface or subsurface of the nucleus. However, it is also known that the activity is usually concentrated in very localized areas of the surface, some of them remaining active even when not illuminated. Usually this leads to the presence of denser regions in the coma which take the form of jets, spirals, or arcs. This phenomenon is less understood, in particular the early stage of jet formation.

In support of the Rosetta mission, we are developing a complex model of cometary activity, simulating all physical processes that lead to the creation of 'jets' of dust and gas from these active areas. In this talk I will present an overview of dust coma structures, from the large ones extending tens of thousands of kilometers away from the nucleus, down to the smallest features seen on the surface by different spacecrafts. We will discuss how modeling these features can contribute a lot to the characterization of the nucleus parameters.

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thur, 05-April-2012
Speaker:   Jeff Morgenthaler (PSI)
Title:  Comets as Molecular/Atomic Physics Laboratories

Abstract: Comets represent nearly ideal laboratories for the study of molecules and atoms that have long dissociative/ionization lifetimes. Interplanetary space can be likened to an infinitely large extreme-high vacuum vessel in microgravity. The Sun is a well-studied light and particle source. Aided by interactions in the collision sphere, a region a few thousand kilometers in radius for typical comets, cometary material expands into this 'vacuum vessel' at speeds of order 1 km/s. Beyond the collision sphere, material travels on ballistic trajectories with essentially no further interactions with cometary material. At this point, the material only interacts with the solar photon field and solar wind. In this laboratory, using wide-field imaging and spectroscopic instruments, I have studied the dissociation rate of OH to excited oxygen (with an unexpected discovery), measured the carbon ionization lifetime, and will soon make a measurement of the CO lifetime. Please join me as I describe my adventures, which include the discovery of "magic snowballs" in comet Hale-Bopp (oxygen molecules produced in a gas phase interaction between OH and O) and the observation that the lifetimes of many long-lived species are likely over-estimated due to inadvertent neglect of solar wind ionization effects.

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thur, 12-April-2012
Speaker:   Stefanie Milam (Goddard)
Title:  Observations of Nitrogen Fractionation in Prestellar Cores: Implications for Meteoritic Hot Spots

Abstract: Isotopically fractionated material is found in many solar system objects, including meteorites and comets. It is considered, in some cases, to trace interstellar material that was incorporated into the solar system without undergoing significant processing, thus preserving the fractionation. In interstellar molecular clouds, ion-molecule chemistry continually cycles nitrogen between the two main reservoirs - N and N2 - leading to only minor 15N enrichments. Charnley and Rodgers showed that depletion of CO removes oxygen from the gas and weakens this cycle such that significant 15N fractionation can occur for N2 and other N-bearing species in such cores. Observations are being conducted at millimeter and submillimeter wavelengths employing various facilities in order to both spatially and spectrally, resolve emission from these cores. A preliminary study to obtain the 14N/15N ratio in nitriles (HCN and HNC) was conducted at the Arizona Radio Observatory's 12m telescope on Kitt Peak, AZ. Spectra were obtained at high resolution (0.08 km/s) in order to resolve dynamic properties of each source as well as to resolve hyperfine structure present in certain isotopologues. This study included four dark cloud cores, observed to have varying levels of molecular depletion: L1521E, L1498, L1544, and L1521F. Previous studies of the 14N/15N ratio towards L1544 were obtained with N2H+ and NH3, yielding ratios of 446 and >700, respectively. The discrepancy observed in these two measurements suggests a strong chemical dependence on the fractionation of nitrogen. Ratios (C,N, and D) obtained from isotopologues for a particular molecule are likely tracing the same chemical heritage and are directly comparable within a given source. Analysis of preliminary data have ratios of 14N/15N of 69-260, suggesting significant fractionation in nitriles when compared to the amines in these targets. Results and comparisons between the protostellar evolutionary state and isomer isotope fractionation as well as between other N-bearing species will be presented.

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thur, 19-April-2012
Speaker:   Stephen Schwartz (UMd)
Title:  Applying Granular Dynamics Simulations to the Surfaces of Solid Solar System Bodies

Abstract: Recent spacecraft visits to bodies of the Solar System show evidence of landslides, granular ponds, and seismic shaking. I will be presenting a numerical tool designed for the study of the granular dynamics that take place on solid bodies of the Solar System. It is an implementation of the Soft-Sphere Discrete Element Method (SSDEM) in the parallel gravitational N-body code pkdgrav, a well-tested simulation package that has provided a great deal of insight into the field of planetary science. Our implementation of SSDEM allows for the modeling of different contact forces between particles in granular material, such as various kinds of friction, including rolling and twisting friction, and the normal and tangential deformation of colliding particles. Such modeling is particularly important in regimes for which collisions cannot be treated as instantaneous or as occurring at a single point of contact on the particles’ surfaces. The validity of our soft-sphere model is checked by reproducing successfully the dynamics of flows in a cylindrical hopper as well as other laboratory experiments. Preliminary simulations of low-speed impact cratering will also be shown.

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thur, 26-April-2012
Speaker:   NO TALK
Title:  NO Speaker

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thur, 03-May-2012
Speaker:   Hal Weaver (APL)
Title:  The Exploration of Pluto and the Kuiper Belt with the New Horizons Mission

Abstract: The New Horizons (NH) mission was selected by NASA in November 2001 to conduct the first in situ reconnaissance of Pluto and the Kuiper belt. The NH spacecraft was launched on 2006 January 19, received a gravity assist from Jupiter during closest approach on 2007 February 28, and is currently heading for a flyby encounter with the Pluto system. NH will study the Pluto system for ~7 months beginning in early 2015, with closest approach currently planned for 2015 July 14 at an altitude of ~12,500 km above Pluto's surface. NH carries a sophisticated suite of seven scientific instruments, altogether weighing less than 30 kg and drawing less than 30 W of power, that includes panchromatic and color imagers, ultraviolet and infrared spectral imagers, a radio science package, plasma and charged particle sensors, and a dust counting experiment. These instruments enable the first detailed exploration of a new class of solar system objects, the dwarf planets, which have exotic volatiles on their surfaces, escaping atmospheres, and satellite systems. NH will also provide the first dust density measurements beyond 18~AU and cratering records that document both the ancient and present-day collisional environment in the outer solar system down to sizes of tens of meters. However, the recent discovery of a new satellite (provisionally named 'P4'), together with the earlier discoveries of Nix and Hydra, has heightened concern that debris in the Pluto system, generated by impacts on these small satellites, might jeopardize the NH spacecraft as it flies through the system at ~14 km/s. As a result, the NH Project has undertaken a multi-pronged effort, involving both modeling and observations, to investigate and mitigate this potential hazard. Assuming that the NH spacecraft and instruments remain healthy after the Pluto flyby, and if NASA approves an extended mission phase, the NH spacecraft will be targeted toward a flyby encounter with one or more small (~50 km diameter) Kuiper belt objects (KBOs) after the Pluto flyby; an intensive search for candidate KBOs using large ground-based telescopes has already begun.

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thu, 10-May-2012
Speaker:   Daniel Jontof-Hutter (UMD)
Title:  Magnetic Field Effects on Dusty Rings

Abstract: Micrometeoroid impacts onto tiny moonlets orbiting near Jupiter replenish the dusty rings with grains of all sizes. These grains become electrically charged from interactions with the ambient plasma and solar photons, and their orbital motions are dominated by gravity and the electromagnetic force arising from Jupiter's rotating magnetic field. For even the simplest case of constant electric charge, this combination of forces causes both radial and vertical dynamical instabilities. When the gravitational and electromagnetic forces are comparable, positively-charged dust grains are driven to either crash into Jupiter or escape from the planet depending on their launch distance. Some smaller grains of either charge are vertically unstable, climbing up local magnetic field lines to collide with Jupiter. With numerics and analytics, we map out these instabilities for all grain sizes and launch distances (Jontof-Hutter and Hamilton 2012).

Further dynamical instabilities arise when charges vary with time due to, for example, a dust grain's periodic transit through Jupiter's shadow which temporarily interrupts photoelectric currents. The eccentricities of large grains, which react nearly instantly to changes in the charging environment, are excited enough to explain the faint outward extension of Jupiter's Thebe ring (Hamilton and Krueger 2008). We expand our investigation by exploring the effect of Jupiter's shadow on dust grains of all sizes, both inside and outside synchronous orbit. The shadow extends the radial instability zones discussed above to both larger and smaller dust grains. The removal of larger grains is limited by the orbital precession timescale, a few months at the main ring, and longer further out. Smaller grains, which react slowly to differing charging conditions, suffer forces that are alternatively stabilizing and destabilizing if their electric potentials change sign. These grains evolve chaotically and most eventually become unstable.

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


Date:   Thu, 17-May-2012
Speaker:   NO PALS
Title:  ACM conference

Abstract:

For further information please contact PALS coordinator Dr. Sebastien Besse at sbesse@astro.umd.edu, 301-405-9922.


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