LPI Seminar Series
2003
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 RecordingsJanuary 2003
Wednesday, January 15, 2003 - Hess Room - Brown Bag Seminar, 12:00 PM
James Oberg (<a href="www.jamesoberg.com">www.jamesoberg.com</a>)
Sleuthing Russian Space Secrets
From a lifelong interest in 'Sleuthing Soviet (and now Russian) Space Secrets', author and space program veteran James Oberg will discuss time-tested workable principles in obtaining reliable insights into the Russian space program as a basis for successful and mutually satisfactory international cooperation -- governmental, commercial, academic, news media, and more -- with the Russian space industry. This richly-illustrated talk will describe successful sleuthing strategies as applied to past, current, and future aspects of the Russian space program.
Friday, January 17, 2003 - Berkner Room, 3:30 PM
Dr. Burkhard Dressler, Lunar and Planetary Institute
Slate Islands Impact Structure, Canada
The Slate Islands archipelago in northern Lake Superior represents the central uplift of a 30-32-km complex impact structure. Target rocks are Archean supracrustal and igneous rocks and supracrustal Proterozoic rocks. The size of the structure is defined by the bathymetry around the island group and by a seismic survey. Shatter cones occur on all islands and are up to >10 m long. Pseudotachylites, impact glasses, shock metamorphic features, and the shatter cones were generated during the contact and compression phase of the impact process, followed during excavation, central uplift and central uplift collapse, by polymict, clastic matrix breccias in the uplifted target rocks, and by allogenic fall-back breccias (suevite and "bunte breccia"). On Mortimer Island and some of the other outlying islands, monomict, autoclastic breccias occur. They were probably formed relatively late, i.e. during central uplift, central uplift collapse and/or crater modification. These conclusions are based on field observations (e.g. cross-cutting relationships) and petrography (e.g. observation of rock fragments containing planar deformation features -PDFs - in "younger" breccias). - We assigned shock pressures to >100 specimens from all across the archipelago applying a standard universal stage method on 20 quartz grains with PDFs per sample. The resulting shock attenuation plan is irregular/roughly concentric. - Based on a 40Ar-39Ar release spectrum of a pseudotachylite sample, the age of the structure is approximately 436 Ma.
Friday, January 24, 2003 - Berkner Room, 3:30 PM
Dr. Lavern D. Stasiuk, Geological Survey of Canada
Application of Organic Petrology to Studying Ancient Life on Earth: Potential Method for Identifying Organics and Biological Entities in Meteorites and Planetary Samples
The most established method for recognizing and evaluating in situ, micron-scale organic matter within rocks is organic petrology. Organic petrology techniques are classically used for studying/application of carbon and hydrogen-based organic matter in geology and industry. These include the coal and coke industry, carbon-based material sciences, petroleum (oil and gas) industry, archaeology and the mineral exploration industry. Reflected light microscopy, fluorescence microscopy and confocal laser scanning fluorescence microscopy are the main systems used to evaluate both the micro-morphology and to quantify visible light region optical properties of organic materials. Optical properties such as per cent reflectance, degree of anisotropy and visible light region fluorescence provide a constraint on the maximum temperature the organic matter has been exposed to. In geological applications, organic petrology is used to identify, characterize, and classify biologically-derived organic matter preserved within recent sediments which have seen limited geothermal alteration (i.e. < 1Ma; < 30 °C) and within ancient rocks which have undergone significant geothermal alteration at elevated temperatures (up to 1.6-2.2 Ga and older; 40 to ~ 250 °C). This talk will be an exhibition of optical and laser microscopy of Recent and ancient floral-, algal/bacterial-, faunal-, and fungal - derived in situ organic matter within rocks and associated bio-mineralization. The emphasis will be on illustrating biological organic matter not readily recognized using other microscope techniques (e.g. SEM). In this context, the talk will illustrate anomalous microscopic biological components such as intracellular biological entities (e.g. zoospores; cellular division) and organics and microfossils from the Precambrian which are not typically considered to be present in rocks of this age.
February 2003
Friday, February 14, 2003 - Berkner Room, 3:30 PM
Neil R. Banerjee, University of Alberta
Life on the Rocks: Bioalteration of Volcanic Glass in Modern and Ancient Oceanic Rocks as a Proxy for Studies of Extraterrestrial Material
Over the past decade, the existence of a deep subsurface biosphere has been increasingly discussed. Microbial alteration of basaltic glass from in situ oceanic samples and ophiolites is perhaps one of the most exciting recent discoveries. However, the very existence of relics or true fossils of early life has proven to be very controversial. In this talk we suggest that an unlikely substrate, altered marine basalt, may preserve early indicators of ancient biological activity. We discuss the use of petrological, geochemical, and microbiological methods for the detection of microbial activity within modern marine basalts and ophiolites. By using a combination of methods we are able to convincingly demonstrate the presence of microbial activity. We also demonstrate that geochemical traces of microbial life are preserved through geological time, possibly as far back as the Archean. We believe oceanic basalts may provide a good terrestrial analogue for studies of extraterrestrial samples. Since basalts are likely to be returned by any extraterrestrial sample return mission, they should be assessed for their potential in recording biological traces. Our techniques could be easily applied to samples returned from Mars and other extraterrestrial bodies where liquid water and conditions suitable for life may have existed.
Friday, February 21, 2003 - Berkner Room, 3:30 PM
Tori M. Hoehler, NASA Ames Research Center
Thermodynamics at the geology-biology interface: Bioenergetic boundary conditions for subsurface life
Microbial ecosystems based on the energy supplied by water-rock chemistry carry particular significance in the context of geo- and astrobiology. With no direct dependence on solar energy, lithotrophic microbes could conceivably penetrate a planetary crust to a depth limited only by temperature or pressure constraints (several kilometers or more). The deep lithospheric habitat is thereby potentially much greater in volume than its surface counterpart, and in addition offers a stable refuge against inhospitable surface conditions related to climatic or atmospheric evolution (e.g., Mars) or even high-energy impactors (e.g., early in Earth's history). The possibilities for a deep microbial biosphere are, however, greatly constrained by life's need to obtain energy at a certain minimum rate (the maintenance energy requirement) and of a certain minimum magnitude (the energy quantum requirement). The mere existence of these requirements implies that a significant fraction of the chemical free energy available in the subsurface environment cannot be exploited by life. Quantification of these parameters in terrestrial microbial ecosystems will establish a criterion of "energetic habitability" that will help to guide the search for subsurface life. Our early work has focused on quantifying the second of these constraints (the biological energy quantum) in near-surface microbial communities that metabolize H2 - a potential substrate for subsurface life. In systems where energy is limiting, these organisms become extremely efficient in their metabolism, and can apparently survive with only half the energy yield previously thought necessary to support life. Lowered energy requirements imply that a correspondingly greater proportion of the planetary subsurface could represent viable habitat for microorganisms.
Friday, February 28, 2003 - Berkner Room, 3:30 PM
Thomas Greathouse, University of Texas at Austin
TEXES: A High-resolution Mid-infrared Spectrograph, and a Study of Saturn's Stratosphere
TEXES, the Texas echelon-cross-echelle spectrograph, operates between 5 and 25 microns. It has multiple modes of operation capable of resolving powers, lambda/(delta lambda), of approximately 100000, 20000, 3000, and imaging. I will give an overview of its design and a sample of some science attempted thus far. It is mounted at the NASA IRTF and is open to the astronomical community for collaborative projects.<br><br>The second part of the talk will focus on my own research of Saturn's stratosphere. I will present results from a latitudinal scan of Saturn using TEXES in September 2002. We retrieved spectra of methane emission lines between 1228 and 1233 cm-1 at a resolving power of 95,000. Thermal profiles required to model the spectra reveal large temperature variations with latitude which is an effect of Saturn's current season, southern summer.
March 2003
Thursday, March 6, 2003 - Berkner Room, 3:30 PM
Essam Heggy, Bordeaux Astronomical Observatory, France
Water Exploration in the Martian Subsurface Using Low Frequency Sounding Radars
The Mars Exploration Program has identified the search for subsurface water as a key investigation for understanding the geologic and hydrologic history of the planet and identifying potential environments for the survival of primitive life forms.<br><br>During the coming decade several geophysical tools will be used to address this task and reduce the ambiguities concerning the total abundance of water and its distribution as ground ice and groundwater. The search for groundwater will be conducted by three sounding radars, on three separate missions, whose ability to detect and identify the presence of liquid water will be strongly dependent on the petrology, mineralogy and the thermal structure of the Martian subsurface - properties that define the electrical characteristics and geological environment of the sounded sites.<br><br>In this talk, I will describe some problems associated with the geophysical exploration for water using electromagnetic methods - focusing mainly on the potential science return from the 2 MHz Ground Penetrating Radar that will be flown onboard the 2007 Netlander mission. This interdisciplinary study has included sample preparation of Martian soil analogues, soil electromagnetic characterization in the laboratory, geological and geo-electrical modeling of potential landing sites, simulations of radar wave propagation in arid volcanic environments and recent field tests of a prototype instrument in the western Egyptian desert.>
Friday, March 7, 2003 - Lecture Hall, 3:30 PM
Walter Kiefer, Lunar and Planetary Institute
Gravity Evidence for Extinct Magma Chambers on Mars: Looking at the Magmatic Plumbing
Gravity observations by Mars Global Surveyor provides evidence for high density structures beneth three large highland volcanoes, Syrtis Major, Tyrrhena Patera, and Hadriaca Patera. The spatial association between the gravity anomalies and the volcanos indicates that the buried structures are extinct magma chambers that are now at least partially filled with dense cumulate minerals. In each case, the magma chamber is several hundred kilometers across and at least 3 to 5 kilometers thick. These observations provide our first look at the magmatic plumbing system of Mars.
April 2003
Monday, April 7, 2003 - Hess Room - Brown Bag Seminar, 12:00 PM
Pierre Hudon, NASA-Johnson Space Center
The Origin and the Effect of Pressure on Liquid-liquid Miscibility Gaps of Binary Oxide Systems
An exhaustive review of compositional and thermal extents of miscibility gaps in 61 binary silicate, borate and germanate systems permits identification of four groups of cations exhibiting different immiscibility behaviors. The first group comprises network-modifier cations with an ionic radius larger than about 87 pm. They have coordination numbers equal to, or higher than, 5 and their miscibility gap size increases linearly with increasing ionic potential. The second group involves cations with an ionic radius smaller than about 87 pm (in octahedral coordination). They have at least two coordination numbers: the first one is always 4 and the other 5 (or more, usually it is 6). For this reason they are called amphoteric. Their miscibility gap sizes decrease with an increase of the ionic potential. The third group includes transitional cations. They are characterized by larger miscibility gap sizes than expected when they are compared with cations with similar ionic radii despite the fact that some of them (e.g. Cr3+) may behave as an amphoteric element because their ionic radii in octahedral coordination are smaller than about 87 pm. The fourth group involves highly polarizable cations possessing a lone pair of electrons. This group of cations has smaller miscibility gap sizes than expected when they are compared with cations with similar ionic radii. The effect of pressure on these four groups is discussed in the context of planetary differentiation.
Friday, April 11, 2003 - Lecture Hall, 3:30 PM
Prof. Joan Johnson-Freese, Naval War College, Newport, RI
The Chinese Manned Space Program: Sun Tzu or Apollo Redux?
A chain reaction of space activity, begun by Soviet-U.S competition in the 1960's, has been duly catalyzed by China's own manned space effort. The Middle Kingdom began its ventures into space in 1999, but soon it hopes to be only the third nation to have achieved human spaceflight. If this does happen, China's position vis-α-vis the world - and particularly vis-α-vis the US - is bound to change forever. Through taking the step into space, China hopes to move closer to bridging the "technology gap" with the US and thereby enhance its national, regional and international position. And as an extra practical bonus, jobs for scientists and engineers, and education and specialized training for other technical personnel should lead to an overall advancement of Chinese technology and more economic growth. What really has Washington sitting up, however, is that Chinese space efforts will - indeed already do - include militarization. These activities not only encroach heavily upon the uncontested US dominance of space, but also could make the US even more aggressive in its military space activity. - YaleGlobal<br><br>This article is accessible at <a href="http://yaleglobal.yale.edu/display.article?id=1177">http://yaleglobal.yale.edu/display.article?id=1177</a>
Friday, April 18, 2003 - Berkner Room, 3:30 PM
Joe Hahn, Lunar and Planetary Institute
The Secular Evolution of the Primordial Kuiper Belt
A broad overview of our current understanding of the Kuiper Belt will be provided by describing the conditions under which Kuiper Belt Objects (KBOs) accrete, as well as the Belt's subsequent dynamical evolution. Of particular interest are the KBO orbits which indicate that this population has since suffered considerable dynamical excitation. This may in part be due to Neptune's early orbital expansion into the Kuiper Belt. However planet migration cannot explain all of the Belt's structure, so other mechanisms are also implicated. This may include the scenario recently described by Rodney Gomes, who showed that the Belt could have been `invaded' by other interlopers that formed elsewhere. Although the evidence for this `invasion' is compelling, this mechanism is also very inefficient at stirring up the Belt. The remainder of my talk will thus describe another mechanism that can be quite effective at stirring up the Kuiper Belt.<br><br>In particular, I will examine the secular perturbations that the giant planets exert in the Kuiper Belt. Secular perturbations are the slow forcings that occur on orbital precession timescales, and these forces can excite large disturbances at secular resonances. However the early Kuiper Belt was quite massive and dynamically undisturbed, and under these conditions, secular resonances tend to excite very long wavelength spiral waves that can propagate across about the Belt's entire radial extent. A model has been developed to study the propagation of spiral waves in the primordial Kuiper Belt, and the cosmogonic implications of this form of wave-action will be described further
Thursday, April 24, 2003 - Lecture Hall, 3:30 PM
Michelle Minitti, Arizona State University
Assessing the Effect of Impact Shock on Water in Amphibole: Implications for the Martian Meteorites
Hydrous phases in the martian meteorites, kaersutite (Ti-rich amphibole) and apa tite, have unique and unusual water contents (low) and H isotopic compositions ( D-rich). Understanding the origins of the water contents and H isotopic signatur es of these phases is important to understanding the water budget of Mars and th e interactions between interior, hydrospheric and atmospheric water reservoirs o n Mars. One potential factor influencing water in martian meteorite hydrous phas es is impact shock, the very process that brought the martian meteorites to Eart h. We have investigated the effects of impact-induced devolatilization on the wa ter content and H isotopic composition of amphibole in order to assess the degre e to which water in martian amphibole was influenced by the shock process.
Tuesday, April 29, 2003 - Hess Room - Brown Bag Seminar, 12:00 PM
Yaoling Niu, Department of Geosciences, University of Houston
No Connection Between Mantle Plumes and Ancient Oceanic Crust
One of the advances in modern geochemistry is the recognition of compositional heterogeneities in the Earth's mantle through studies of oceanic basalts. Ocean island basalts (OIB) are particularly variable in composition such that several isotopically distinct mantle source end-members are required to explain the variability. It is generally considered that the mantle compositional heterogeneity is a consequence of plate tectonics by means of crust-mantle recycling. Among many contributions endeavoring to understand the origin of mantle compositional heterogeneity is the classic model by Hofmann and White "Mantle plumes from ancient oceanic crust" [EPSL, 57, 421-436, 1982.]. While some details are considered conjectural, the principal idea of the model has been widely accepted by the solid-Earth community as being, to a first order, correct. Consideration of petrology, geochemistry and mineral physics suggests that ancient subducted oceanic crusts CANNOT be the source materials supplying OIB. Deep portions of recycled oceanic lithosphere are important geochemical reservoirs hosting volatiles and incompatible elements as a result of metasomatism taking place at the interface between the low-velocity zone and the cooling and thickening oceanic lithosphere. These metasomatized and recycled oceanic lithosphere is the most likely candidates for OIB sources [Niu et al., EPSL, 199, 327-345, 2002].
May 2003
Friday, May 2, 2003 - Berkner Room, 3:30 PM
Dr. Simon Kattenhorn, University of Idaho
Breaking the Ice: Europa's Enigmatic Crust
Europa's ice crust is pervasively fractured as a result of tidal stress induced deformation. The resemblance of Europan fractures to several types of terrestrial analogs (joints and faults) has enabled the use of the same fracture mechanics principles applied to Earth to reconstruct the geologic history of many areas of Europa in the context of the global tidal stress history. This has allowed estimates to be made of the amount of reorientation of Europa's ice shell with respect to the interior, due to nonsynchronous rotation. However, the documented mechanical origin of many types of Europan fractures has become increasingly controversial, particularly with regards to whether fractures originated in tension or in shear. Nonsynchronous rotation estimates based on tension fracture assumptions may thus be in error. An important consideration for determining the viability of a tensile fracture hypothesis is whether Europan fractures penetrate through the entire crustal thickness to tap into (and extrude material from) an underlying ocean. Accurate crustal thickness estimates are crucial in this regard. I will present the results of fracture-mechanics-based analyses of Europan features that provide clues to ice thickness and the likelihood that Europan fractures were able to penetrate through the ice shell, providing potential access sites to an underlying ocean.
Friday, May 16, 2003 - Lecture Hall, 3:30 PM
Dr. Chris Herd, Lunar and Planetary Institute
Magmatic Water in Martian Meteorites: Evaluating the Trace Element Evidence
According to some, the zoning of the light lithophile elements (namely Li, Be and B) in pyroxene in the Shergotty and Zagami martian meteorites show evidence of the degassing of magmatic water. These authors argue that the observed decrease in Li and B from cores to rims is due to the separation and degassing of a magmatic fluid, in which Li and B were dissolved. Obviously, such a claim has important implications for the water budget of Mars. Numerous questions arise, such as, How do these elements partition under anhydrous conditions? Can such zoning be explained by the uptake of Li and B by another mineral? How do these elements behave in a natural anhydrous basalt? How well-defined is the zoning of the light lithophile elements in the martian samples?<br><br>I have addressed these questions through a unique combination of experiments on synthetic material and analyses of natural samples. Results of experiments carried out at the Johnson Space Center and Ion Probe analyses of martian and eucrite basalts at the University of New Mexico have quantified the partitioning of Li and B in anhydrous basalts and have provided new insights into martian basalt petrogenesis.
June 2003
Friday, June 20, 2003 - Lecture Hall, 3:30 PM
Dr. Julia Morgan, Rice University
The Failure and Stabilization of Kilauea Volcano: Seismic Surveys, Submersible Dives, and Numerical Simulations
Recent aseismic and coseismic ground displacements along the south flank of Kilauea volcano, HI, have revealed the presence of a large, predominantly submarine, landslide, the Hilina Slump. Over the years, there has been much debate regarding the extent and geometry of this landslide, and the associated geologic hazards if it were to fail catastrophically (e.g., Ward, 2002, Nature, 415). New multichannel seismic reflection data and high-resolution bathymetry collected over the submarine slopes of Kilauea volcano in 1998, now provide constraints on the subsurface structure of the Hilina slump. Observations from these data suggest that the landslide is, in fact, becoming more stable, rather than less. This appears to be a consequence of the catastrophic collapse of an adjacent portion of Kilauea's south flank in the recent past, and the subsequent offscraping of the landslide debris by seaward spreading of the volcano flank. A broad bench constructed in front of the mobile flank now serves to buttress the active Hilina slump, probably reducing the likelihood of future catastrophic detachment. Time permitting, I will demonstrate the validity of our structural interpretations with discrete numerical simulations of volcano flank dynamics.
Friday, June 27, 2003 - Lecture Hall, 3:30 PM
Dr. Allan Treiman, Lunar and Planetary Institute
The Geologic Settings of Martian Gullies: Recent Liquid Water at Mars' Surface, or Something Else?
Gully landscapes in craters and canyons on Mars have been interpreted as sure proof that liquid water was present, at Mars' surface, within the last tens of thousands of years. This despite the fact that liquid water is thermochemically unstable (not permitted) at or near Mars' surface. Many ideas have been proposed to reconcile these geologic and theoretical observations, nearly all involving novel ways to produce liquid water where it should not occur.<br><br>I've investigated the geologic settings of the Martian gullies, and find that they are not consistent with any proposed way of producing liquid water. Instead, geologic relationships suggest that gullies formed from dry flows of wind-deposited silt and dust.
July 2003
Friday, July 11, 2003 - Berkner Room, 3:30 PM
Dr. Russell Shapiro, Gustavus Adolphus College
Fossilized Bacteria from Methane Seeps as an Analogue for an Extraterrestrial Fossil Record
This talk will present the findings of ongoing research into the microbial paleontology of the Cretaceous Tepee Buttes of Colorado as an analogue for an extraterrestrial fossil record. The Tepee Buttes are a series of carbonate mounds that precipitated in the presence of seafloor methane. Preliminary work on the Tepee Buttes has demonstrated the preservation of bacterial body fossils (likely methanotrophs and sulfide reducers) and authigenic sulfide production. By understanding the paleontology of the buttes, as well as the complex petrographic fabrics, we can develop proxies for recognizing ancient methane-driven carbonates in the rock record and aid astrobiologists in the search for an extraterrestrial fossil record.
August 2003
Friday, August 15, 2003 - Lecture Hall, 3:30 PM
Herve Gregoire-Mazzocco, University of Padua, Italy
Analysis of Meandering Channels on Mars
Analyzing common meandering channels that we observe on Martian surface, we try to understand the erosion processes that lead to such landforms. Using a theoretical framework developed for the study of meandering channels on Earth, Martian topography data from the MOLA altimeter, and the famous data set from the work of Leopold, we provide evidence for common structures of Martian and Terrestrial meanders, independent of gravity, basic erosion properties, relevant dynamics and fluid properties. This evident link between Martian and Earth landforms, and a statistical analysis of the meandering features on Mars showing their immaturity, suggest that they were probably formed by massive catastrophic flows, driven by gravity or density gradients, over short periods of time.
Friday, August 22, 2003 - Lecture Hall, 3:30 PM
Dr. Robert Herrick, Lunar and Planetary Institute
Oblique Impacts on the Terrestrial Planets
Nearly all planetary impacts occur at nonvertical angles, and half occur at angles less than 45 degrees from horizontal. Oblique impact affects crater efficiency, morphology, shape, and ejecta distribution. Numerical models and small-scale experiments have been used to study the process of oblique impact, but verification from the planetary cratering record has been primarily anecdotal. I will present results from systematic surveys of the cratering record on the moon, Venus, and Mars. Inferences about the oblique impact process from these surveys can be compared to predictions from models.
September 2003
Friday, September 5, 2003 - Lecture Hall, 3:30 PM
Dr. Michael Zolensky, Johnson Space Center
Stardust and Hayabusa Mission Updates: Time to Think Small
The Stardust Mission, launched in 1999, will in all likelihood be successfully returning coma dust from comet Wild II, as well as fresh interstellar dust, in January 2006. With the May launch of the Hayabusa asteroid sample return mission (formerly Muses-C), there are now two flying spacecraft which are slated to return dust and chips from primitive solar system bodies. I will provide summaries of the Stardust and Hayabusa sample return mission science goals, and updates on the missions themselves. For both missions there are upcoming funded opportunities to participate in the preliminary sample analyses ($$).
Friday, September 12, 2003 - Lecture Hall, 3:30 PM
John Lindsay, NASA Johnson Space Center
Defining the Abiotic/Biotic Boundary: Evidence from the Archaean of Australia
Until recently it had been assumed that life began early on Earth, perhaps before or at least by 3.8 Ga and that relatively sophisticated cyanobacteria had appeared by at least 3.4 Ga. Recently, however, serious doubts have been raised about the validity of this early evidence. The Pilbara Craton of Western Australia includes a relatively continuous successions of volcanic and sedimentary rocks extending from 3.5 to 1.9 Ga, the critical period during which the earliest life was evolving on Earth. The environmental setting in which life first emerged appears to have been dominated by hydrothermal processes that, because of their unusual chemistry, had the potential to emulate and perhaps synthesize life itself.
Friday, September 19, 2003 - Lecture Hall, 3:30 PM
Dr. Francis Nimmo, University College, London
Flexure and Topography on Europa
Apparently flexural features on Europa may be used to infer the rigidity of the ice shell, and thus the total ice shell thickness. The thickness thus derived is ~20km, similar to independent estimates based on crater studies and tidal dissipation calculations.<br><br>Flexure does not appear to be a major cause of positive topography in bands, extensional features similar to mid-ocean ridges on Earth. Lateral shell thickness variations cannot maintain topography over geological timescales. Lateral density variations are a more likely cause of positive topography. These density variations could be caused by variations in either porosity or salt content. The latter hypothesis suggests compositional convection may be important, and could help to explain apparently diapiric surface features.
October 2003
Friday, October 3, 2003 - Lecture Hall, 3:00 PM
Dr. William McKinnon, Washington University, St. Louis
Io: A New View of Its Interior, Redox Evolution & Lithosphere, and Lessons for the Hadean Earth
Beyond the spectacular visible and infrared images, the Galileo mission provided remarkable insights into the inner workings of a superheated "terrestrial" planet. Gravity field measurements imply a substantial metallic core, almost certainly liquid, and in concert with cosmochemical constraints these measurements provide bounds on the amount of partial melt in the silicate mantle (providing an answer to the question of whether Io has a magma ocean). HST determinations of volcanic plume gas composition confirm the 20-yr-old prediction of J.S. Lewis that Io's interior is oxidized, but Io was even more oxidized in the past (a legacy of the conditions of its formation)! And the lithosphere (and crust) of Io, counterintuitively, turns out to be rather thick, leading to some rather exotic volcano-tectonic models. This last point implies that our admittedly fuzzy picture of the Hadean Earth may need revision.
Friday, October 17, 2003 - Lecture Hall, 3:30 PM
James Farquhar, University of Maryland
Insights into the Earth's Early Atmosphere and Sulfur Cycle
Anomalous sulfur isotope (mass-independent) signatures have been recently documented in the earth's early geological record. These signatures have been attributed to atmospheric chemical reactions and are providing new approaches to the study of atmospheric evolution and evolution of Earth's sulfur cycle. For example, it is presently thought that the presence of this signature in rocks older than 2.45 billion years old, but not in rocks younger than 1.9 Billion years old provides one of the strongest lines of evidence for an early, low oxygen atmosphere. This seminar will discuss the nature of the geological sulfur isotope record, its interpretation, and its implications for Earth's early environments.
Friday, October 24, 2003 - Lecture Hall, 3:30 PM
M. Darby Dyar, Mount Holyoke College
Where's the Water in Mars?
While current Mars research is focused on the presence of water and/or hydrous phases on the martian surface, an equally provocative question is the location and quantification of water in the martian interior. This is a critically important issue on most terrestrial planets because mantle minerals constitute the largest reservoir of hydrogen in many planetary bodies, and thus control the water budget for those bodies. Furthermore, hydrogen controls the mechanical properties of rocks even when it is present at ppm levels. It is therefore critical to constrain the H contents of anhydrous phases in samples not only from Mars, but from other terrestrial bodies.<br><br>Interpretation of direct measurements of H contents is complicated by the mobility of the H atom, which may be lost during crystallization, subsequent re-equilibration, shock, excavation, and transport of meteorites. Fortuitously a record of the lost H may be recorded by the presence of excess charge on the Fe atoms in the crystal structure. In the Fe-bearing minerals that constitute the majority of mantle phases on terrestrial bodies, such dehydrogenation can occur via the reaction H+mineral + Fe2+mineral = 1/2[H2]gas + Fe3+mine ral. The kinetics of this mechanism are well-constrained for mantle phases, but they require than both H and Fe3+ be constrained. Thus, we prese nt here direct measurements of H and Fe3+ in mineral separates from SNC meteorites using M÷ssbauer, r eflectance and transmitted light FTIR spectroscopy. Our results show that both olivines and pyroxenes in SNC's contain H in amounts comparable to what is observed in terrestrial mantle samples. The gradual release of this water into the martian crust from i ntrusions could feed into subsurface water and ice deposits, and episodic release of hydrogen via volcanic eruptions would have dramatic effects on atmospheric evolution.
November 2003
Wednesday, November 12, 2003 - Hess Room - Brown Bag Seminar, 12:00 PM
Sarah Noble, Brown University
Turning Rock Into Regolith - Space Weathering in the Inner Solar System
Any body that does not have an atmosphere to protect it should suffer the effects of space weathering, however those processes are dependent on their environment (e.g. soil composition, bombardment rate and velocity, distance from the sun, strength of gravity, temperature, existence of a magnetic field, etc.), and thus should vary from body to body. "Space weathering" may therefore look different on Mercury or the asteroids than it does on the Moon. It appears, for example, that the extreme temperature range on Mercury may have significant consequences for the properties of space weathering there. As for the asteroids, as we have no direct regolith samples from these bodies with which to compare to our lunar samples, we have been comparing and contrasting lunar regolith breccia samples to meteoritic regolith breccias in order to try to understand regolith processes on asteroids. In addition, we have created a synthetic optical analog for space weathering products that allows us to investigate how the optical properties of space weathered material changes under different conditions. By revealing the differences in weathering effects distance from the sun, strength of gravity, temperature, existence of a magnetic field, etc.), and thus should vary from body to body. "Space weathering" may therefore look different on Mercury or the asteroids than it does on the Moon. It appears, for example, that the extreme temperature range on Mercury may have significant consequences for the properties of space weathering there. As for the asteroids, as we have no direct regolith samples from these bodies with which to compare to our lunar samples, we have been comparing and contrasting lunar regolith breccia samples to meteoritic regolith breccias in order to try to understand regolith processes on asteroids. In addition, we have created a synthetic optical analog for space weathering products that allows us to investigate how the optical properties of space weathered material changes under different conditions. By revealing the differences in weathering effects distance from the sun, strength of gravity, temperature, existence of a magnetic field, etc.), and thus should vary from body to body. "Space weathering" may therefore look different on Mercury or the asteroids than it does on the Moon. It appears, for example, that the extreme temperature range on Mercury may have significant consequences for the properties of space weathering there. As for the asteroids, as we have no direct regolith samples from these bodies with which to compare to our lunar samples, we have been comparing and contrasting lunar regolith breccia samples to meteoritic regolith breccias in order to try to understand regolith processes on asteroids. In addition, we have created a synthetic optical analog for space weathering products that allows us to investigate how the optical properties of space weathered material changes under different conditions. By revealing the differences in weathering effects with different environments and compositions, we can begin to understand the fundamental processes of space weathering and the relative importance of the many external and internal factors involved. This knowledge will allow us to make more accurate predictions about the effects of exposure to the space environment on bodies from which we have no samples, which in turn will allow us to more accurately interpret remotely sensed data of those bodies.
Friday, November 14, 2003 - Lecture Hall, 3:00 PM
Dr. Elizabeth Turtle, Lunar and Planetary Laboratory, University of Arizona
Modeling the Deformation of Landforms on Mars by Creep of Ground Ice
A suite of mid- to high-latitude surface features on Mars has been attributed to viscous flow phenomena associated with near-surface deposits of ground ice (Squyres et al. 1992), an interpretation that is consistent with recent Mars Odyssey GRS observations indicating a high water content close to the Martian surface (Boynton et al. 2002). Squyres (1989) identified two classes of creep-related landforms:<ol><li>softened terrain resulting from in situ viscous deformation, and<li>debris aprons produced by mass wasting along escarpments.</ol>We are using finite-element analysis, incorporating recent measurements of the rheological parameters for water-ice/particulate mixtures, to simulate the deformation of impact craters and debris aprons by viscous creep of ice-rich permafrost. By comparing our model results to the structural and topographic characteristics of landforms that we have documented using MGS MOC and MOLA data, we can constrain the conditions necessary for such deformation to occur. Our simulations demonstrate that even under present Martian conditions flow can occur quite rapidly, ~10,000 years. However, if the mobility of the ice is restricted by a surface layer that resists deformation, or the high volume fractions of ice inferred from GRS data to be present near the surface do not persist to significant depths, deformation timescales could be significantly longer.
Friday, November 21, 2003 - Lecture Hall, 3:30 PM
Prof. ErzsΘbet MerΘnyi, Rice University
Intelligence in the Service of Planetary Science
Computational Intelligence (CI) has been my mathematical fascination for the past ten years. This period included eight wonderful years in the Lunar and Planetary Lab at the University of Arizona, which induced me to respond with CI methods to analysis challenges posed by spectral (especially hyperspectral) data, for the identification of planetary surface materials. I have been using Self-Organizing Maps (SOMs), a major Artificial Neural Network (ANN) line of CI, to put a magnifying lens on various planetary data in the way of clustering and pattern recognition. ANNs are massively parallel, very finely distributed learning architectures (connectionist machines) that mimic, in a simplified way, the information processing of the nervous system. They excel in pattern recognition, classification, non-parametric regression and other tasks. SOMs represent a special, major ANN family with resemblance to neural maps that form in the brain and which spatially organize sensory input patterns for maximally effective information processing. Examples are the tonotopic maps in the auditory, and the retinotopic maps in the visual cortex. In the smaller half of my talk I will present background on this amazing, biologically inspired learning paradigm and its presently known clustering and data mining capabilities. Then I will show a sampling of works that I did in collaboration with astronomer, planetary scientist, geologist and geophysicist colleagues in Mars, asteroid, moon and Earth research, and how these works resulted in improved answers to scientific questions. For example, clustering of 60-color asteroid data (almost ten years ago!) revealed the long-suspected olivine and pyroxene end groups of S asteroids that could not formally be identified earlier, and it also provided other clarifications of the taxonomy. Classification of 300-band telescopic Mars images, in spite the 150 km footprint, identified a new, crusted soil type on Mars, and a hematitic region in Sinus Meridiani, before Global Surveyor and Pathfinder visited. Recently, I have been looking at newly calibrated Mars Pathfinder IMP images in preparation for comparison with data that we will be receiving from the Mars Exploration Rover mission. I will also show a preliminary mapping of spectral species from this investigation.
