LPI Seminar Series


The LPI Seminar Series brings prominent scientists to the LPI to present on a broad array of scientific disciplines that advance our understanding of the solar system. The seminar series, which began in September 1969, has brought many notable contributors from numerous research and academic institutions to the LPI. Seminars are typically held on Thursdays from 3:00-4:00 p.m. US/Central, but dates and times are subject to change. All seminars will be held virtually until further notice.

Sign up for LPI Seminars to receive email notifications of upcoming seminars and details on how to join the virtual seminar. For more information, please contact Patrick McGovern ([email protected]) and Sam Crossley ([email protected]).

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.

View Recordings  

January 2005

Friday, January 21, 2005 - Lecture Hall, 3:30 PM
Amy Ross, NASA JSC Advanced EVA Group
Learning by Doing: EVA System Design for Mars

The Advanced Extravehicular Activity (EVA) group at JSC is preparing for surface exploration of the Moon and Mars. A key component in the preparations has been and will continue to be field testing. Through the Desert Research and Technology Studies (RATS) field testing the performance characteristics of current systems and the requirements for future surface exploration systems are being determined. The presentation will discuss the history of field testing performed by the Advanced EVA group and objectives for the 2005 RATS testing. Additionally, the discussion will include a primer on space suit design, descriptions of surface exploration hardware that has been evaluated (icluding rovers, robots and science tools), an overview of field test results, and surface science concepts. Finally, areas of future activity and opportunities for participation will be presented.

Friday, January 28, 2005 - Lecture Hall, 3:30 PM
Allan Treiman, Lunar and Planetary Institute
Martian Gullies: Geology and Groundwater

Tens of thousands of gullies have been found on steep slopes all over Mars. These recent landforms have been identified by most researchers as water-rich debris flows, despite the fact that liquid water is not stable at or near Mars' surface now. Most researchers have suggested that the Martian gullies represent outflows of groundwater, either produced locally by solar heating or regionally by volcanic or other processes. However, the geology of most gully occurrences are inconsistent with groundwater. Most gullies are on the walls of impact craters, where [1] rock is too shattered to hold groundwater, and [2] rock layers (as they are) tilt away from the gully-bearing walls. Many gullies are found near the tops of isolated knobs, places distant from regional groundwater (in the absence of abundant precipitation). And gullies do not necessarily face downhill on regional slopes. So, groundwater is unlikely to be involved in gully formation and other mechanisms (like dry granular flows) must be considered.

February 2005

Friday, February 11, 2005 - Lecture Hall, 3:30 PM
Philippe Paillou, Bordeaux Astronomical Observatory, France
Discovery of the Largest Impact Crater Field on Earth in the Gilf Kebir Region, Egypt

Using orbital imaging radar, we have detected tens of circular structures in the south-western Egyptian desert, covering more than 4500 km2 close to the Gilf Kebir plateau in sandstones of Upper Cretaceous. Fieldwork confirmed that it is a new impact crater field: 13 craters from 20m to 1km in diameter were studied. The impact origin was confirmed by the observation of shock-related structures such as shatter cones and planar fractures in quartz grains of breccia. Considering the extension of the crater field, it was possibly created by several meteorites which broke up when entering the Earth's atmosphere.

Friday, February 18, 2005 - Lecture Hall, 3:30 PM
Tom Stepinski, Lunar and Planetary Institute
Martian Paleoclimate from Morphology of Drainage Basins

Morphologies of Martian and terrestrial drainage basins are encapsulated by their circularity functions enabling objective and quantitative comparison. A neural net technique is used to construct a geomorphic similarity map for a population of basins. First, we study a control population of terrestrial basins for which climate data is available. We establish a correlation between basin's morphology and climate. Second, we study a sizable population of terrestrial and Martian basins. We find a systematic difference between morphologies of basins on the two planets. By extrapolating morphology-climate correlation to Martian basins, this difference could be understood in terms of climatic differences with Martian basins developing in extremely dry (by terrestrial standards) climate.

Friday, February 25, 2005 - Lecture Hall, 3:30 PM
Andrew Steele, Carnegie Institution
Life Detection Technology Testing on the Arctic Mars Analogue Svalbard

To avoid ambiguous results in both the robotic and sample return missions to Mars, instruments must be rigorously tested in challenging analogue environments on earth. We have undertaken 2 field seasons testing instruments including enzyme based life detection techniques as well as protein microarrays in Svalbard. This area is known for the worlds most northerly hotsprings and for carbonate globules that resemble those found in ALH84001. I will present field and laboratory data on samples gathered on the AMASE expedition.

March 2005

Friday, March 4, 2005 - Lecture Hall, 3:30 PM
M. N. Rao, Lockheed Martin Space Operations
Evaporative Evolution of Martian Brines Based on Cl and Br in Nakhla Secondary Salts and MER Rock-rind Samples

We report Br abundances determined by Adanced Photon Source X-Ray Microprobe and Cl determined by Electron-Microprobe in Nakhla fracture-filling secondary salts and find that these values are close to the halogen abundances determined by APXS in Gusev and Meridiani rock samples. Br an Cl are know to be conservative tracers in aqueous brine solutions. By comparing the halogen abundances in nakhlites with those of Gusev and Meridiani rock-rind samples, we suggest that the low Br (and Cl/Br ratios) in Lafayette iddingsite seems to represent martian brine solutions during early stages of evaporation, whereas the high Br (and Cl/Br ratios) correspond to the late stages of evaporation of brine solutions near Mars surface. Most of the rock and soil samples examined by APXS at Gusev and Meridiani seem to fall between the Nakhla and Lafayette compositions suggesting that they are similarly of progressive evaporative orgin of brine solutions on Mars.

April 2005

Friday, April 1, 2005 - Lecture Hall, 3:30 PM
Len Srnka, ExxonMobil
Advances in Marine Controlled Source Electromagnetic Exploration

Marine controlled-source electromagnetic (CSEM) methods have been developed within academia, government laboratories, the defense sector, and the oil and gas industry over the past 30 years. Recently, several important advances in acquisition equipment and in 3D data processing have led to a resurgence of interest in this technology. Several CSEM studies of mid-ocean ridges have led to new insights into their structures and evolution. For industrial applications, particularly in hydrocarbon exploration and development, marine CSEM is arguably the most important geophysical technology for imaging below the seafloor since the emergence of 3D reflection seismology some 25 years ago. As this new technology matures, its viability will be tested in a variety of geologic settings and across a range of business applications.<br><br>In this presentation, the fundamental geophysics of marine electromagnetics will first be reviewed. Although the resolution of marine CSEM is low compared to seismic reflection data, considerable knowledge can be gained by integration of CSEM data with other geoscience information. A synopsis will be given of ExxonMobil's research over more than two decades on this technology. Critical stages in this geophysics effort will be highlighted, including the effectiveness of leveraging ExxonMobil's technology development with external organizations. The rapidly evolving technology landscape will be summarized. Finally, a selection of geological applications will be reviewed.

Friday, April 8, 2005 - Lecture Hall, 3:30 PM
Julie Moses, Lunar and Planetary Institute
Seasons on Saturn and Their Effect on Atmospheric Chemistry

Saturn, with its eccentric orbit and 26.7 degree obliquity, experiences seasons in much the same way as the Earth. Moreover, Saturn's ring system casts shadows on the planet and attenuates incident solar radiation for portions of the year. Both the ring attenuation and seasonal dependence of ultraviolet radiation affect the chemical production and loss rates of stratospheric constituents. These effects have not been considered in atmospheric chemistry models to date, and with the Cassini Composite Infrared Spectrometer poised to map hydrocarbon distributions across Saturn, more complex and realistic photochemical models are needed. I will present results from a time-variable, one-dimensional (1-D), seasonal model of stratospheric photochemistry on Saturn. The model accounts for variation in ultraviolet flux due to orbital position, solar-cycle variations, latitude and season, and ring-shadowing effects. The predicted latitude variations of ethane and acetylene from the model are compared with thermal infrared observations acquired with the TEXES spectrometer at the IRTF to determine whether realistic 1-D models can provide reliable predictions of constituent distributions or whether 2-D models that include meridional transport will be needed to explain the observations.

Friday, April 15, 2005 - Lecture Hall, 3:30 PM
Ross Taylor, Australian National University
Geochemistry of the Solar Nebula

The inner nebula was depleted not only in the gaseous and icy components of the original nebula but also in those elements that are volatile below about 1100K. This depletion is observed in most meteorites, except for the Type 1 carbonaceous chondrites (CI) that match the solar photospheric abundances for the non-gaseous elements. The depletion is also observed in the bulk compositions of the Venus, Earth and Mars so that it is a widespread feature within 3-4 AU on the Sun. However, the Sun has CI composition for the non-gaseous elements, so this depletion along with asteroidal and planetary formation occurs late in disk history. The early inner nebula was both bone-dry, as shown by the anhydrous primary mineralogy of meteorites, and depleted in volatile elements. Possible processes responsible for volatile loss may include early solar activity driving out the gaseous and volatile components to a "snowline" around 5 AU, selective evaporation of grains of differing mineralogy drifting into higher temperature zones in the nebula near the early Sun or it may reflect interstellar gas/grain element distribution.<br><br>Volatile element depletion is observed in the components (eg. chondrules) of chondritic meteorites and so occurs before chondrule formation, close to Tzero (4566 ▒ 5 m.y.). Formation of planetesimals and asteroidal-sized bodies occurred rapidly with Vesta (450 km diameter) accreting, differentiating and producing basaltic lavas within a few million years of Tzero. Variations in Fe, Al/Si and Mg/Si from CI are observed in most meteorites, the Earth and Mars (?) indicating that additional major element fractionation has occurred during asteroidal and planetary growth.

Friday, April 29, 2005 - Lecture Hall, 3:30 PM
Berry Lyons, Ohio State University
Analogies to Mars and other Extraterrestrial Locations

For over 40 yrs The McMurdo Dry valleys, the largest polar desert region in Antarctica @ ~ 78 S has been investigated as an analogy to possible past ecosystems on Mars. Since 1993, Taylor Valley has been used as a primary research site for the McMurdo Dry Valleys Long-Term Ecological Research (MCM-LTER) site. The MCM-LTER program involves meteorological, physical, hydrological, geochemical as well as ecological investigations and is the first study to approach the Dry Valleys in an integrated, synthetic manner and study the ecosystem as a whole. In this presentation I will describe the physical setting of the Dry Valleys and discuss how variations in climate drive ecosystem change. I will present information on how both the present and past physical processes in the valleys have generated significant ecological variability there. In addition, I will attempt to draw analogies of this Earth "end-member environment" to Martian potential conditions in the past.

May 2005

Friday, May 20, 2005 - Lecture Hall, 3:30 PM
Roger Summons, Massachusetts Institute of Technology
The Permian-Triassic Extinction Event: Was It an Impact-related Phenomenon or Something Closer to Home?

Much controversy and spirited debate accompanies any discussion of the Permian-Triassic Boundary and the associated mass extinction. Impact of a massive bolide, volcanism, overturn of a stagnant ocean and rapid climate change have all been put forward as potential causes. Various lines of isotopic evidence have been used to show that there was a major perturbation to the marine carbon and sulfur cycles over an extended period and culminating in a sharp negative carbon isotopic excursion that was practically synchronous with the extinction. The carbon cycle anomalies continue well into the Triassic that may well explain the protracted biological recovery. New evidence based on biomarkers shows that the Tethys realm was subject to episodes of euxinia that caused hydrogen sulfide to outcrop in shallow water. In this seminar I will lay out these issues and make the case that the extinction was not the consequence of an impact but of toxic ocean chemistry.

Friday, May 27, 2005 - Lecture Hall, 3:30 PM
David Vaniman, Los Alamos National Laboratory
Hydrous Minerals as Possible Sources of Water in Equatorial Martian Regolith

Neutron spectrometer data from the Odyssey Mars Orbiter provide evidence of water abundances up to ~10 wt% in regolith to a depth of ~1 m in some near-equatorial locations on Mars. Water ice is unstable in these locations, suggesting that some of this water may be present in hydrous silicates (clays or zeolites) or hydrated salts. Viking, Pathfinder, and MER chemical analyses of martian soil indicate that Mg and S are correlated and MgSO4 is a likely cementing or alteration agent. MgSO4 is readily hydrated to salts that include epsomite (7-hydrate; 51 wt% water), hexahydrite (6-hydrate; 47 wt% water), and kieserite (monohydrate; 13 wt% water). Our studies in the Mg-sulfate system include both pure MgSO4 nH2O as well as mixtures with possible regolith constituents such as zeolites, clays, and palagonite. Results indicate that (1) the MgSO4 system is more complex than previously thought, (2) phase changes are pathway dependent and kinetically limited, (3) when emplaced as a brine, Mg-sulfate solutions readily extract Ca from clays, zeolites and palagonite to form gypsum as well as MgSO4 nH2O. Preliminary data suggest that the sulfate-hydrate system could be a significant component of the near-surface water reservoir in martian equatorial regions.

June 2005

Friday, June 3, 2005 - Lecture Hall, 3:30 PM
Karl Kehm, Washington College, Maryland
Measuring Iron Isotopes in Meteorites: Pitfalls and Progress

Recent advances in ICP-MS (inductively coupled plasma mass spectrometry) have stimulated a groundswell of interest in the stable isotope behavior of increasingly heavy elements, particularly iron. This talk will outline some of the inherent difficulties associated with precisely measuring iron isotopes in natural samples, and will describe a technique that we have developed to overcome some of these potential problems. Our lab and several others have reported mass fractionated iron in chondrules from primitive meteorites. Ongoing efforts to decipher this observation will be discussed.

Friday, June 10, 2005 - Lecture Hall, 3:30 PM
Walter Kiefer, Lunar and Planetary Institute
Gravity Models of the Argyre and Isidis Impact Basins, Mars

Friday, June 17, 2005 - Lecture Hall, 3:30 PM
Pat McGovern, Lunar and Planetary Institute
Olympus Mons: the Rise and Fall (and Rise) of a Mountain Paradise

The immense Olympus Mons volcano towers up to 23 kilometers over the Martian lowlands. The bulk of the volcanic edifice was likely constructed via repeated emplacement of effusive lava flows from summit and flank vents. However, Olympus Mons was also shaped by destructive processes: volcanic spreading and sector failure. Flank collapse events generated long runout landslides recognized as the lobate aureole deposits; the headscarps of such slides became the up-to-10-km-tall basal escarpment. Flank spreading at low strain rates also produced upthrust blocks at the northwest and southeast margins of the edifice. The same constructive and destructive processes have been observed in the volcanic paradise of the Hawaiian Islands on Earth. A basal detachment, rooted in low-permeability pelagic sediments where high pore fluid (i.e., water) pressure is generated, enables volcanic spreading and flank collapse at Hawaiian volcanoes. Repeated cycles of construction and destruction characterize the history of such edifices, and I suggest a similar evolution for Olympus Mons, thereby resolving some old controversies about its development. Furthermore, several lines of evidence point to the importance of water, of both deep and shallow origin, in the ancient and recent (ongoing?) structural evolution of the Olympus Mons edifice and aureole. Given the presence of water and a long-lived, recently active, volcanic source of thermal and chemical energy, Olympus Mons may be the last vestige of Paradise for Martian life.

Monday, June 20, 2005 - Lecture Hall, 3:30 PM
Vinciane Debaille
Spatial and temporal heterogeneities of oceanic basalts based on variations in Sr, Nd, Pb and Hf space

Small scale heterogeneities within the upper mantle partly control the geochemical signatures of surface lavas from various tectonic environments. The origin of the presence of geochemically "enriched" material in the mantle is essentially linked to convergence contexts where subduction processes lead to the injection of surface heterogeneous materials (oceanic crust, sediments and fluids) in the peridotitic mantle. The dissemination of this anomalous material in the mantle is then assumed by its convective dynamics.<br><br>In my seminar I will present results of two different studies: one focused on enrichment processes affecting a mantle wedge through an isotopic investigation of lavas from Merapi volcano (Indonesian arc); and a second one dedicated to the expression of mantle heterogeneities far away from subduction areas, at mid-oceanic ridge (north Atlantic from 22 to 35\260N), where magmatic processes directly sample the asthenospheric mantle.<br><br>Finally I will make a short presentation about the applications of isotopic tools that I propose to carry out on lunar samples at LPI.

Friday, June 24, 2005 - Lecture Hall, 3:30 PM
Doug Ming, NASA Johnson Space Center
Geochemical and Mineralogical Indicators for Aqueous Processes in the Columbia Hills of Gusev Crater, Mars

The Mars Exploration Rover (MER) Spirit has explored the rocks, outcrops, and soils around the landing site in Gusev craters for nearly 525 sols (Mars days). Spirit has spent the last 350 sols ascending Husband Hill, which is the highest hill in the Columbia Hills that are located about 2.6 km to the southeast of the landing site. Water played a major role in the formation and alteration of rocks, outcrops, and soils in the Columbia Hills. The extent of alteration ranges from moderately altered to extensively altered materials. Four distinct compositional units were identified: West Spur-Clovis, Husband Hill-Wishstone, Husband Hill-Peace, and Husband Hill-Paso Robles. Columbia Hills outcrops and rocks may have formed by the alteration of basaltic rocks, volcaniclastic materials, and/or impact ejecta by solutions that were rich in acid-volatile elements. However, it is not clear whether aqueous alteration occurred by metasomatism, hydrothermal solutions associated with volcanic or impact processes, aqueous vapors from volcanic eminations (i.e., acid fog weathering), or by low-temperature solutions.

July 2005

Friday, July 15, 2005 - Lecture Hall, 3:30 PM
James Lyons, UCLA
Sources and Sinks of CH4 on Mars

Recent spectroscopic detections of CH4 in the atmosphere of Mars are the first definitive observations of an organic compound on that planet. The relatively short photochemical lifetime of CH4 (~300 years) argues for a geologically young source. We demonstrate here that low-temperature alteration of basaltic crust by carbon-bearing hydrothermal fluid can produce the required CH4 flux of 1 x 107 moles year-1, assuming conservative values for crustal permeability and oxygen fugacity as implied by martian basaltic meteorites. The crustal thermal disturbance due to a single dike ~ 1 x 1 x 10 km intruded during the past 104 years is capable of driving the alteration, if all carbon is supplied by magmatic degassing from a dike with only 50 ppm C. Serpentinization of crustal olivine is another possible source of Mars methane. In this case the source of C is crustal rather than magmatic. Atmospheric methane strongly suggests ongoing subsurface geochemical and possibly magmatic processes on Mars.

Friday, July 29, 2005 - Lecture Hall, 3:30 PM
Essam Heggy, Lunar and Planetary Institute
Low Frequency Radar Remote Sensing: The Unseen Planetary Geology

Over the past several decades, radar remote sensing techniques have provided new insights into the surface and subsurface properties of the Earth, Moon, Venus, Mercury, and Mars - as well as numerous smaller solar system bodies. In my talk I will focus on the Martian case showing the potentials of the low frequency radar remote sensing to map the dust covered geology of Mars. Results from recent sounding radar experiments carried through different earth arid environments and laboratory electromagnetic characterization of Martian-like soils will be discussed.

August 2005

Friday, August 5, 2005 - Lecture Hall, 3:30 PM
Tommy Greathouse, Lunar and Planetary Institute
Evidence for a Mesosphere on Saturn, the Seasonal Variation of Temperature between 2002 and 2004, and a Comparison of Those Variations with Current Seasonal Climate Models

Ground based high-resolution spectral observations of CH4 emission features taken at the NASA IRTF using the TEXES spectrometer on September 13th 2002 and October 14th and 15th 2004, LS of 268.4O and 296.8O respectively, are presented. These data, taken along Saturn's central meridian, are sensitive to the stratospheric temperature between 10 and 0.01 mbar. The 1245 cm-1 observations taken on October 15th, 2004 show distinct self-absorption cores on top of the strong CH4 emission lines. These features indicate that there is a region overlaying the stratosphere which is cooler than the stratopause, ie. a mesosphere. This explanation is supported by detailed line-by-line radiative transfer modeling of the 2004 data.<br><br>A comparison of the 2002 and 2004 stratospheric temperature retrievals shows an enhancement of the 3 mbar thermal gradient between the equator and south pole. An ~10 K increase of temperature between the equator and south pole at the 3 mbar level in 2002 has been described in Greathouse et al. 2005. By modeling the 2004 data, we infer that the equator to pole trend has increased to ~15 K. These results suggest that the phase lag in the thermal response of Saturn's stratosphere is shorter than predicted by the seasonal climate model of Bezard and Gautier 1985. However, the magnitude of the equator to pole temperature variation is still within their predicted range.

Friday, August 26, 2005 - Lecture Hall, 3:30 PM
Jake Maule, Carnegie Institution of Washington
Miniaturized Biotechnology: Enabling the Vision for Space Exploration

A Vision for Space Exploration was presented by the President in 2004 that defined a focus for our nation's space program1. It called for a "human return to the Moon by the year 2020, in preparation for human exploration of Mars"2. In a recent hearing at the House Science Committee, the NASA Administrator cited six specific "high-priority areas [related to] future space exploration activities"1 for the International Space Station (ISS) research program. Included was the area of Advanced Environmental Monitoring and Control (AEMC)3, which includes microbial monitoring both inside and outside of the spacecraft.<br><br>We have adapted a commercial-off-the-shelf (COTS), hand-held microbial monitoring device (called the Portable Test System or PTS) for space flight on the ISS in collaboration with Charles River Laboratories. Scheduled for launch in April 2006 (flight 12A.1), the PTS has already been used for a number of diverse applications: planetary protection (to verify cleanliness of the Mars Exploration Rovers before launch4), environmental monitoring (in the Aquarius underwater habitat5) and in-field microbiology, performed in combination with ATP luminometry and antibody (Ab) microarray analysis at sites of astrobiological interest (e.g. Arctic6, Kamchatka6).<br><br>Ab microarrays have been developed for detection of biomarkers in simulant martian regolith7 and collagen in 10,000 year-old bone8 (further miniaturization of sample handling steps is being carried out with microfluidics at NASA MSFC). This assay is commercially available for the detection of up to 500 human proteins9 and would be an invaluable tool for medical research and monitoring in space. <br><br> <b>Conclusion</b>:Miniaturized biotechnology is available today and is a cost-effective means to address multiple applications relevant to human and robotic space flight: environmental monitoring, planetary protection, life detection and medical research. <br><br> <b>References</b><br> <sup>1</sup>Testimony of NASA Administrator, Michael D. Griffin, at the Review of President's FY2006 Budget, House Science Committee, June 28 2005. <br> <sup>2</sup>Presidential address "The Vision for Space Exploration", by President Bush at NASA Headquarters, Washington D.C., February 2004. NASA document NP-2004-01-334-HQ<br><sup>3</sup>The other five "high-priority areas" cited by NASA Administrator Griffin were "space radiation, health and shielding"; "advanced EVA activities and support"; "human health and countermeasures [and] medical research with human subjects"; "life support systems...and their validation in microgravity"; and "medical care and human factors".<br><sup>4</sup>Wainwright, N.???????? <br><sup>5</sup>Maule, J., Wainwright, N., Pierson, D., Ott, C.M. (2005). Real-time microbial monitoring with the Portable Test System (PTS) in the Aquarius underwater habitat: Correlation with traditional culture-based techniques. Appl. Environ. Microbiol. In prep. 2005<br><sup>6</sup>Maule, J., Toporski, J., Steele, A. (2005). "Antibody microarray analysis in the field to analyze protein expression at hydrothermal sites in Spitsbergen and Kamchatka". Astrobiology, Apr 2005, Vol. 5, No. 2: 275-299. <br><sup>7</sup>Maule, J., Toporski, J., Steele, A. (2005). Labeling and detection of biological molecules in Mars analog regolith using an antibody microarray. Astrobiology, Apr 2005, Vol. 5, No. 2: 289. <br><sup>8</sup>Maule, J., Fogel, M., Steele, A. (2005). Detection of human and bovine collagen in early Holocene bone and teeth using an antibody microarray. Astrobiology, Apr 2005, Vol. 5, No. 2: 290.

September 2005

Friday, September 9, 2005 - Lecture Hall, 3:30 PM
Clive Neal, University of Notre Dame
Large Igneous Provinces: Results of 20 Years of Reseach Into Earth's Largest LIP<br><br>The Ontong Java Plateau (OJP) is the worlds largest "LIP" that covers an area about the size of western Europe. Almost all of it lies beneath sea-level, with a few sub

Friday, September 30, 2005 - Lecture Hall, 3:30 PM
Paul Warren, University of California, Los Angeles
Core Formation in Partially Molten Planetesimals: The Ureilite Meteorites"

Ureilites are the second most abundant and in many ways the most distinctive type of achondrite. They are, in essence, extremely depleted peridotites, with virtually zero observable feldspar, but ~3 wt% carbon, usually as intergranular "veins" of semi-amorphous (but probably graphite-derived) "C-matrix." Ureilites were once widely viewed as igneous cumulates, but today most researchers interpret then as asteroidal mantle restites. Our group at UCLA has applied INAA to study several tens of ureilites for trace elements. Ureilites display strong correlations among siderophile ratios such as Au/Ir, Ni/Ir, Co/Ir, As/Ir, Se/Ir and Sb/Ir. Without exception, the ureilites have siderophile abundances too high to be consistent with formation as cumulates. Ureilite siderophile depletion patterns loosely resemble fractionations, presumably nebular in origin, among carbonaceous chondrites. However, a tight correlation between Au and Ni extrapolates to the low-Ni/Au side of the compositional range of carbonaceous chondrites. From this mismatch, mild depletions of "noble" siderophile elements such as Ir and Os, and moderate depletions of siderophile/chalcophile elements such as Ni, Au and As, we infer that ureilite siderophile fractionations are largely the result of igneous removal of S-rich metallic melt, possibly with minor entrainment of Fe-metal. Asteroidal core formation probably occurs in two discrete stages. In general, separation of a considerable proportion (several wt%) of S-rich metallic melt probably occurs long before, and at a far lower temperature than, separation of the remaining S-poor Fe-metal. Apart from the Fe-metal itself, only extremely siderophile elements wait until the second stage to sequester mainly into the core.

October 2005

Monday, October 10, 2005 - Lecture Hall, 3:30 PM
Brad Thomson, Brown University
Recognizing Impact Glass on Mars Using Surface Texture, Mechanical Properties, and Mid-infrared Spectroscopic Methods

A primary goal of future Mars sample return missions will be to obtain samples whose isotopic ages can be used to place absolute time constraints on the relative Martian crater chronology. Thus, identifying the origin of surface material as impact or volcanic prior to its return to Earth will be critical. This talk will focus on strategies for identifying and characterizing impact melt breccias both from landed and orbital perspectives. In addition, a reanalysis of orbital data of the Viking 2 Lander site will be presented that indicates the dominance of impact and eolian processes, thus calling into question suggestions of recent (post Late Hesperian) oceanic, lacustrine, or glacial activity in the northern plains of Mars.

Friday, October 14, 2005 - Lecture Hall, 3:30 PM
Natasha Johnson, NASA Goddard Space Flight Center
Venus, Water and Tremolite

Venus is an extremely hot and dry planet. However, decomposition studies of a hydrous mineral, tremolite, suggest that this particular mineral can survive the current conditions on Venus' surface. If this is the case and Venus had water in its past, hydrous minerals may have formed. If so, we might be able to detect these minerals today. This detection would give hard evidence of water in Venus' history.

Friday, October 28, 2005 - Lecture Hall, 3:30 PM
Oded Aharonson, California Institute of Technology
Subsurface Ice on Mars with Rough Topography

High latitude ground ice on Mars may be explained, in part, by thermal stability and the abundance vapor in the Martian atmosphere. Local slopes alter surface and subsurface temperatures substantially, and hence allow ground ice to persist at locations where it would otherwise be unstable. Global statistics of the topography of Mars derived from MOLA are computed, processed, and extrapolated to derive a description of surface roughness on spatial scales to which ground ice should be sensitive. This slope distribution, with a global of Hurst exponent of approximately 0.81, is convolved with the predictions of a new thermal model for the dependence of subsurface ice on slope. We find that due to topographic slopes, ground ice can reside in locations where previous global models predict it to be unstable, down to latitudes of about 25 degrees in both hemispheres. This area includes, for example, the northern Olympus Mons aureole deposits, Hecates Tholus, and Hellas basin. In the highest latitudes slopes reduce the amount of buried ice, while in lower latitudes the ice fraction increases, smoothing the boundary of the ice table.

November 2005

Friday, November 4, 2005 - Lecture Hall, 3:30 PM
Susan Sakimoto, University of Notre Dame
Is It Dead Yet? Martian Volcanism and Hydrovolcanic Activity: Recent Data and Changing Views

Our views of martian volcanism and water-volcano interaction have been dramatically changed by mission data from 1997 onward. The recent data have forced us to re-evaluate most aspects of our knowledge in the field: 1) the possibilities of recent or ongoing volcanism and volcano-related water movement; 2) the distribution and styles of volcanism; 3) the relative ages of volcanic events and centers; and the physics and chemistry of the emplacement of volcanic and volcanic-related materials. We will discuss how the views have changed, and what data have been key in instrumenting change, as well as taking a look at specific aspects of martian volcanism through our "new eyes."

Friday, November 18, 2005 - Lecture Hall, 3:30 PM
Landon Moore, Johnson Space Center
RESOLVE Project Overview

The RESOLVE project was initiated by NASA in January of 2005 to develop a package capable of characterizing the extant resources in the lunar polar craters and demonstrating technologies critical to in-situ resource utilization. Members of the RESOLVE team come from five NASA centers, three universities, and multiple industry partners. Recently, RESOLVE was named in the NASA headquarters announcement for the RLEP2 mission which will land a payload near one of the poles in the 2011 time frame.

Monday, November 21, 2005 - Hess Room, 3:30 PM
Chris Herd, University of Alberta
The Occurrence of Baddeleyite in Martian Meteorites: Implications for In Situ Geochronology

Recent advances in microbeam analytical techniques (laser ablation ICP-MS, SIMS) have enabled the in situ determination of radiogenic isotopic compositions. Results of U-Pb analysis of zircon using LA-ICP-MS with a spot size < 40 microns show highly precise and reproducible Pb-Pb and U-Pb ratios. Application to terrestrial igneous and metamorphic rocks has proven fruitful in determining ages from U-Pb bearing mineral phases in thin sections.<br><br>Geochronology of shergottites (martian basalts) is a difficult and time-consuming task. Although in situ methods cannot provide the same precision as ID-TIMS, they may provide a means of determining preliminary ages for martian meteorites, provided that relevant mineral phases are sufficiently large, and the beam sufficiently small.<br><br>Geochronology of shergottites (martian basalts) is a difficult and time-consuming task. Although in situ methods cannot provide the same precision as ID-TIMS, they may provide a means of determining preliminary ages for martian meteorites, provided that relevant mineral phases are sufficiently large, and the beam sufficiently small.<br><br>Baddeleyite (ZrO2) is a common accessory mineral in martian basalts. A study of its occurrence was carried out by looking for baddeleyite in a suite of martian meteorites, including Chassigny, the shergottites Zagami (dark mottled lithology), NWA 3171, and NWA 1460, and the olivine-phyric shergottites NWA 1068 and Dar al Gani 476. Baddeleyite was found in all but one of these samples, enabling some generalizations about its occurrence. Grain sizes range from < 5 microns to > 40 microns, opening up the possibility of in situ geochronology.

December 2005

Friday, December 2, 2005 - Lecture Hall, 3:30 PM
Scott McLennan, State University of New York at Stony Brook
Surficial Processes on Mars: a Planet on Acid

Chemical and mineralogical observations and inferences made by the Mars Exploration Rovers Spirit and Opportunity, located in very different geological settings on opposite sides of the planet, are consistent with fluid-rock interactions taking place at low pH. Under acidic conditions many chemical relationships characteristic of terrestrial weathering do not apply: Al and Fe are more soluble, Si mobility is governed by fluid/rock ratios and iron oxidation is sluggish. Chemical components of late Noachian to early Hesperian sedimentary rocks studied by Opportunity at Meridiani Planum were formed by evaporative processes and diagenetically altered in acidic groundwater. These processes led to a distinctive suite of chemically precipitated minerals including Fe-, Mg- and Ca-sulfates, hematite, amorphous silica and possibly Mg-, Ca-, Na- and/or Fe-chlorides, but apparently no carbonates. Amazonian basaltic rock surfaces examined by Spirit on the Gusev plains and in the Columbia Hills were altered by small amounts of acidic water in the near-surface environment and typically show evidence of thin mm-scale rinds of mineral dissolution that mimic trends revealed by martian basalt alteration experiments. Thus, aqueous alteration at low pH appears to be one hallmark of surfical processes throughout most of recorded geological history on Mars. Such a history must be reconciled with the extreme buffering capacity that should be provided by a planetary crust dominated by basalt.

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