LPI Seminar Series
Effective January 1, 2009, LPI seminars will be held on Thursdays.
LPI seminars are held 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 Axel Wittmann (phone: 281-486-2105; e-mail: wittmann@lpi.usra.edu) or Jeremie Lasue (phone: 281-486-2195; e-mail: lasue@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.
February 2010
- Thursday, February 11, 2010 - Lecture Hall, 3:00 PM
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Jim Kasting, Penn State University
Early Mars was WarmMars has fluvial features over much of its surface which suggest that its climate was much wetter in the distant past, but there is considerable disagreement as to how warm the planet’s climate must have been to form them. Climate modelers (including this one) have had difficulty reproducing warm martian paleoclimates, in part because of Mars’ distance from the Sun, and in part because the Sun itself was less bright at that time. Other groups (e.g., Segura et al., Science, 2002) have suggested that Mars’ climate was warm only transiently, and that the fluvial features were formed by rainout of steam atmospheres created by large impact events. I will show that this latter hypothesis is unlikely, as the amount of water needed to carve the valleys was much larger than this model allows. Ways of augmenting the greenhouse effect of a dense CO2 early martian atmosphere will be discussed.
- Thursday, February 18, 2010 - Lecture Hall, 3:00 PM
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Ulrich Riller, School of Geography and Earth Sciences and Origins Institute, McMaster University, Hamilton, Canada
Origin of pseudotachylite in terrestrial impact basinsPseudotachylite bodies in impact structures are dike-like and consist of angular and rounded wall-rock fragments enveloped by a microcrystalline and sporadically glassy matrix that crystallized from a melt. Knowledge of the formation of pseudotachylite bodies is important for understanding mechanics of complex crater formation. Most current hypotheses of pseudotachylite formation inherently assume that fragmentation and melt generation occur during a single process, either by (1) shock loading, (2) frictional shearing, or (3) decompression. Based on the structure and of pseudotachylite bodies and chemical composition of matrices at the Sudbury and Vredefort impact structures we show that these processes differ in time and space. We demonstrate that the cm- to km-scale bodies are effectively fragment- and melt-filled tension fractures that formed by differential rotation of target rock during cratering. Highly variable pseudotachylite characteristics can be accounted for by a single process, i.e., drainage of initially superheated impact melt into tension fractures of target rocks during late stages of crater formation.
- Thursday, February 25, 2010 - Lecture Hall, 3:00 PM
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Dan Durda, SwRI, Boulder, CO
"Ejecta blocks as tracers of the formation and evolution of asteroid regoliths"Regoliths on small bodies represent valuable natural laboratories for evaluating various models of impact cratering processes since they may present crater structures or ejecta features that either do not form or are hidden on higher-gravity bodies like the Moon. Quantifying the extent to which impact processes generate and redistribute regoliths on small body surfaces is pivotal to the issue of how to relate meteoritical samples to their asteroidal parent bodies and a better understanding of the processes at work in these unique environments is crucial for designing technologies and techniques for future robotic and human exploration, resource utilization, and impact hazard mitigation. Ejecta blocks represent the coursest fraction of small body regoliths and are important, readily-visible 'tracer particles' for crater ejecta blanket units that may be linked back to specific source craters, thus yielding valuable information on physical properties and constraining various aspects of impact cratering in low-gravity environments.These blocks, launched from the surface of a small, rapidly-rotating, and highly-elongated and irregularly-shaped body, are subjected to a complex dynamical process. Dynamical models of reaccretion of impact ejecta on asteroids thus provide important and necessary tools for a detailed investigation of the distribution and morphology of blocks and finer regolith across their surfaces.
March 2010
- Thursday, March 11, 2010 - Lecture Hall, 3:00 PM
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William T. Reach, Infrared Processing and Analysis Center (IPAC), Caltech
TBA - Thursday, March 18, 2010 - Lecture Hall, 3:00 PM
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Dan Boice, SwRI, San Antonio, TX
TBA - Thursday, March 25, 2010 - Lecture Hall, 3:00 PM
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Chris Herd
Heterogeneous Organic Matter in the Tagish Lake Meteorite: Implications for the Origin of Prebiotic Molecules Heterogeneous Organic Matter in the Tagish Lake Meteorite: Implications for the Origin of Prebiotic MoleculesOrganic compounds are observed in star-forming regions of space. Such compounds were present during the formation of our Solar System, as they were incorporated and preserved in carbonaceous chondrite meteorites. Organic matter in carbonaceous chondrites exists as two components: compounds that are soluble in polar organic solvents, and insoluble organic matter (IOM), which is a kerogen-like, macromolecular material. Soluble organic compounds include those of pre-biotic interest, including amino and carboxylic acids. The Tagish Lake meteorite fell on January 18, 2000 onto the frozen surface of Tagish Lake in northern B.C. Samples of the meteorite were recovered within a week of the fall and kept frozen and untouched by hand. The meteorite is an ungrouped carbonaceous chondrite, containing 2.5 wt % organic carbon. The circumstances of its fall and retrieval provide a unique opportunity to study organics in the early Solar System; Tagish Lake is the world's most pristine meteorite. The Tagish Lake meteorite is heterogeneous, with a range of macroscopic characteristics, including differences in the proportions of matrix and chondrule-like objects, and mineralogy. Remarkably, these lithological differences are borne out in differences in the organic matter: IOM in different samples varies in terms of H/C and H isotopic composition over a range that encompasses several carbonaceous chondrite groups; soluble organics vary from sample to sample in abundance and type. Ongoing work on amino acids shows a larger complement in our samples than previously observed. These results suggest that aqueous alteration on the asteroid parent body has played a role in the modification (destruction and/or synthesis) of interstellar organic matter, and have significant implications for the mechanisms involved in the formation of pre-biotic compounds, and the delivery of such compounds to the early Earth and other planets.
April 2010
- Thursday, April 8, 2010 - Lecture Hall, 3:00 PM
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Devendra Lal, Scripps Institution of Oceanography, University of California at San Diego
TBA - Thursday, April 15, 2010 - Lecture Hall, 3:00 PM
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Susan L. Brantley, Earth and Environmental Systems Institute, Penn State
TBA - Thursday, April 22, 2010 - Lecture Hall, 3:00 PM
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Christine Floss, Washington University in St. Louis
TBA
May 2010
- Thursday, May 6, 2010 - Lecture Hall, 3:00 PM
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Scott Murchie, Applied Physics Laboratory
TBA - Thursday, May 13, 2010 - Lecture Hall, 3:00 PM
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Amy Louise Morrow, Stanford University
TBA - Thursday, May 20, 2010 - Lecture Hall, 3:00 PM
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Deanne Rogers, Stonybrook State University of New York
TBA
