LPI Seminar Series
LPI seminars are held on most Fridays from 3:00–4:00 p.m. in the Lecture Hall at USRA, 3600 Bay Area Boulevard, Houston, Texas. Refreshments are served at 4:00 p.m. For more information, please contact Justin Filiberto (phone: 281-486-2118; e-mail: filiberto@lpi.usra.edu) or Michelle Kirchoff (phone: 281- 486-2116; e-mail: kirchoff@lpi.usra.edu). A map of the Clear Lake area (PDF format) is available here. The Acrobat Reader 8.0 is available from Adobe. This schedule is subject to revision.
See also the Rice University Department of Physics and Astronomy Colloquia and the Department of Earth Science Colloquia pages for other space science talks in the Houston area.
November 2008
- Friday, November 21, 2008 - Lecture Hall, 3:00 PM
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Jon Friedrich, Fordham University
Three-dimensional petrography of chondritic meteorites: examining the physical evolution of asteroids with synchrotron x-ray microtomography.Synchrotron x-ray computed microtomography (XMT) can be used to generate high resolution three-dimensional (3D) volumetric representations of chondritic meteorites. To examine the role of impacts in the evolution of asteroids as seen through their chondritic offspring, we have performed a quantitative 3D study of metal grains in a suite of increasingly shocked L chondrites with XMT. Our data allow rigorous quantification of size number distributions and collective morphology of Fe(Ni) metal phases in chondritic meteorites. At the resolution of our XMT measurements (8.4–17.9 μm/voxel), the number of metal particles increase with higher degrees of petrographically identified shock loading, indicating a coalescing of Fe–Ni metal at or below this scale. Additionally, our results demonstrate that collective degrees of metal grain preferred orientation increase with greater degrees of impact-related compaction and shock loading. Ductile metal grains in L chondrites collectively begin to demonstrate whole rock foliation at peak shock pressures <5 GPa, pressures great enough to compact and indurate loosely bound chondritic material, and our results constitute evidence for multiple generations of impact events acting on the L parent body or bodies. Additionally, results and the implications of investigations of the nature of pore spaces in uncompacted ordinary chondrites will be discussed.
December 2008
- Wednesday, December 3, 2008 - Lecture Hall, 3:00 PM
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Renu Malhotra, University of Arizona (40th Anniversary Seminar Series Speaker)
Bombardment History of the Terrestrial PlanetsThe Moon and all the terrestrial planets were resurfaced during a period of intense impact cratering that occurred between the time of their accretion, ~4.5 billion years ago, and ~3.85 billion years ago: the crater record and radiometric dating of lunar rocks attests to this conclusion. However, identifying the source(s) of those planetary impactors has proven elusive; speculations have included comets, asteroids, and fragments of a shattered 'large planetesimal'. I will describe compelling evidence that the source of the impactors was the main asteroid belt, and that the dynamical mechanism that caused the so-called 'Late Heavy bombardment' ~3.9 billion years ago was unique in the history of the Solar System and distinct from the processes producing the flux of objects that currently hit planetary surfaces. The Late Heavy Bombardment was a rain of asteroids dynamically ejected from the main asteroid belt, possibly due to the effects of orbital migration of Jupiter and Saturn.
January 2009
- Thursday, January 29, 2009 - Lecture Hall, 3:00 PM
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John F. Mustard, Brown University
Hydrated minerals on Mars and their geologic environments: Implications for the history of waterPhyllosilicate and sulfate hydrated minerals were first definitively identified on Mars from orbit by the OMEGA (Observatoire pour la Mineralogie, L'Eau, les Glaces et l'Activitié) instrument on board Mars Express. Global mapping showed that sheet silicates are widespread but largely found in terrains of Noachian age while sulfates were localized in the region of Valles Marineris, Aram Chaos, Meridiani, and dunes in the northern plains. In contrast to sulfates, phyllosilicate formation requires moderate to high pH and high water activity. A major hypothesis evolving from this discovery is that the conditions necessary for phyllosilicate formation were specific to the Noachian, the earliest era in Mars' history and sulfate formation evolved subsequent to that as Mars experienced massive global change. I will explore this hypothesis incorporating new high spatial resolution, precision pointing, and nested observations by the Context Imager (CTX), Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), and the High Resolution Imaging Sci-ence Experiment (HiRISE)) on the Mars Reconnaissance Orbiter (MRO). These data provide enhanced capabilities to analyze surface mineralogy across the planet and determine the nature and geologic setting of hydrated mineral deposits. Analysis of the diversity of phyllosilicates, associated hydrated minerals, and their geologic setting based on integrated OMEGA-CRISM-MRO analysis will be covered and the implications considered.
