Effective January 1, 2011, LPI seminars will be held on Fridays.
LPI seminars are held from 3:30–4:30 p.m. in the Lecture Hall at USRA, 3600 Bay Area Boulevard, Houston, Texas. Refreshments are served at 4:30 p.m. For more information, please contact Georgiana Kramer (phone: 281-486-2141; e-mail: email@example.com) or Patricia Craig (phone: 281-486-2144; e-mail: firstname.lastname@example.org). A map of the Clear Lake area is available here. This schedule is subject to revision.
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Our perception of the environment and processes acting on Mars during the Noachian has swung several times between a cold, dry Mars with localized erosion by groundwater sapping to a wet, warm Mars with precipitation, runoff, and widespread denudation. At present the pendulum is swinging toward the latter interpretation. This presentation will review the evidence for a water-rich early Mars, emphasizing landforms on the southern highlands of Mars and new evidence from MOLA and MOC.
Owing to hydrogen's extremely high diffusivity (and, incidentally, abundance in the universe), it makes more sense to balance oxidation reactions among minerals by subtracting hydrogen rather than by adding oxygen. That is, under normal conditions hydrogen (gas) is infinitely more easily gained or lost than oxygen, which mainly is tightly bound in mineral structures as the oxide ion, and doesn't diffuse through much as a gas. (Oxygen gas will, however, selectively diffuse through certain defect-rich oxide ceramics at very high temperatures, the basis for one possible technology for recovering oxygen from the CO2-rich martian atmosphere.) Ultimately, of course, all redox reactions involve gain or loss of electrons; the oxidant (e.g., oxygen or sulfur or chlorine) gains electrons; the reductant (e.g., hydrogen or a metal) loses electrons. Each oxygen atom normally gains 2 electrons (oxide ion); under special conditions (e.g., UV irradiation of dry surfaces), it can gain 1 or fewer (peroxide or superoxide ions). These latter ions are themselves strong oxidants that have been proposed (mainly on the basis of the Viking gas exchange experiment, in which free oxygen gas was released by humidified martian soil) to be metastable components of the martian surface. In any case, the martian surface appears to be far more oxidized and oxidizing than any comparable surface on Earth, despite the abundance of molecular oxygen in the terrestrial atmosphere. Under such circumstances, what would be the fate of any iron-bearing hydrous phases (e.g., ordered clays or disordered palagonites) on the martian surface? I suggest that they would probably lose much of their hydrogen, turning them in to oxy-clays, metastable phases with the original crystal structure largely preserved, but with oxide in place of hydroxide. (Charge balance is preserved by oxidizing ferrous to ferric iron.) To my knowledge, oxy-clays have been little studied as possible spectral matches for the martian surface, despite my 1988 suggestion (19th LPSC; seconded by Roger Burns in 1993) that they could be common. Hydrogen loss can occur in a vacuum as well as on planetary surfaces, and can therefore explain partial oxidation of hydrous iron-bearing phases in meteorites (which otherwise are generally reduced).
Possibly 60 or more extrasolar planets have revealed themselves to precision-doppler searches. But soon we will have direct detection techniques which can separate planet photons from stellar photons, and maybe even allow us to take spectra of extrasolar planets. I'll discuss two promising photon-sorting devices, nulling interferometers and coronagraphs with Band-limited masks, and describe some of the science being done by precursors to the planned planet-finding missions. I'll also describe some recent advances in our understanding of what many extrasolar planetary systems may look likeûmassive planets on eccentric orbits in clouds of dust.
I will discuss how partially molten systems, formed during fractional crystallization, evolve. The talk will be concerned with the evolution of an accumulating crystal mush in a basaltic magma chamber. I will start by discussing the anatomy of the crystal pile both from the standpoint of the solids and the liquids. I will then discuss the results of numerical models of compaction and show how these simulations can be used to predict features of cumulates that can be subsequently studied in the field. The loss of liquid from the crystal pile has important consequences for the textures and compositions of the cumulates preserved. I will present field evidence for the escape of evolved liquids from the crystal pile. Lastly I will discuss how interstitial liquid evolving within a crystal pile interacts with the cumulus minerals - using an example of an amphibole oikocryst studied by laser ICP-MS.
The talk will present an overview of Ar-Ar ages of several types of meteorites, and will combine these with other pertinent data sets such as Pb-Pb and Rb-Sr ages, Pu fission track densities, and Ni metallographic cooling rates (as available) to examine possible thermal histories and cooling rates of parent bodies of several types of meteorites.
If rains occurred on Mars during a warm, wet early interval, carbonate "caliche" should have developed on upland basalts during weathering and could be widely present today within vesicles and fractures protected from "sand blasting". Such caliche is widespread in terrestrial basalts and contains a unique isotopic biosignature as well as embedded organic material. Simple detection of this brilliant white material in cracks and vesicles in future missions would confirm that Mars indeed had a "warm, wet early period". By analogy with terrestrial examples, the material itself could contain microfossils, organic molecules, and a strong isotopic biosignature if microbial life had been present in this early stage of martian history. Carbonate in ALH 84001 may be an actual example of altered martian caliche.
Precision topographic field measurements can now be obtained for a variety of landforms by using the constellation of Global Positioning System (GPS) satellites and receivers capable of making Differential GPS corrections. The lecture will review the basics of both GPS and DGPS operations using examples from the Carrizozo lava flow in New Mexico and stabilized sand dunes near Parker, Arizona. The examples illustrate how cm-precision data can be applied to problems in geomorphology, where the shape of the landform is used to learn about the processes that led to its formation. Precision topography of landforms is important for developing constraints for evaluating remote sensing data of both the Earth and of other planetary surfaces.
The vapor deposition model of space weathering will be discussed. The changes in the optical properties of regoliths of silicate bodies without atmospheres, including spectral darkening, reddening and obscuration of absorption bands, are due to submicroscopic metallic iron, and not impact-vitrified glass, as commonly assumed. The iron particles are created during the deposition of vapor generated by both solar wind sputtering and meteorite impact vaporization. The history of the model will be briefly reviewed. It will be shown to be able to account quantitatively for changes in lunar optical properties, and to predict the alteration of spectra of ordinary chondrites to more closely resemble those of S-asteroids. Applied to Mercury, it implies that this body has a regolith in which FeO is low (~2-6%), but not completely absent.
Three-dimensional computer simulations of the geodynamo, the mechanism in the Earth's fluid outer core that maintains the geomagnetic field, now span more than a million years, using an average computational time step of about 15 days. At the surface of the model Earth, the simulated magnetic field has an intensity, an axial dipole dominated structure, and a westward drift of the non-dipolar structure that are all similar to the Earth's. The model's solid inner core, being magnetically locked to the eastward fluid flow above it, rotates slightly faster than the surface of the model Earth. This computer modeling result served as a prediction for the Earth that recent seismic analyses now support. Several spontaneous reversals of the magnetic dipole polarity have also occurred during the simulations, similar to those seen in the Earth's paleomagnetic record. However, no global convective dynamo simulation has yet been able to afford the spatial resolution required to simulate strongly turbulent convection, which surely must exist in the Earth's low-viscosity fluid core. A series of short movies will illustrate the current results and the challenges involved in developing improved, turbulent models.
Vladimir Ivanovich Vernadsky (1863-1945), who is regarded as one of the founders of modern biogeochemistry, has stated in "Scientific Thought as a Planetary Phenomenon" (1991:120) that "the biosphere appears in biogeochemistry as a peculiar envelope of the Earth clearly distinct from the other envelopes of our planet." One of the distinctive features of living matter is the tendency to occur in sheets, laminae, and multilaminar structures that often include sediment particles. The objective of our study is to develop and to present a catalogue of microbial structural signatures in sediments, sediment surfaces, but also in the growth of macroorganisms such as Bryozoa (Moss animals). Moving from the actualistic viewpoint to rock records, structures of microbial, metazoan and abiotic origin may thus be recognized, and provide evidence on facies-dependent biological activities in bygone terrestrial and aquatic environments.
Lamination often indicates the presence of microbial or microbially dominated biosystems. Furthermore, laminated structures are an important borderline to distinguish micro- and macroorganisms, although such a distinction is relative. Both the presence and absence of lamination are lawful phenomena based on the fundamental physical and biological/biogeochemical principles.
A number of simulation experiments provide interesting results related to the origin of life. Interstellar ice analogs made of H2O, CH3OH, NH3, CO and CO2 were ultraviolet-irradiated in a high vacuum at 12 K. Sixteen 13C-labelled amino acids, including 6 proteinaceous ones, were identified as racemic in the room temperature residue. The 'STONE' experiment was designed to test whether Martian sedimentary material could survive terrestrial atmospheric entry. A basalt, a dolomite and artificial Martian regolith were embedded into the ablative heat shield of Foton 12. The collected entry samples were analysed for their chemistry, mineralogy and isotopic compositions. Beagle-2, the exobiology lander of ESA 2003 Mars Express mission, comprises an integrated suite of instruments to optimize the search for evidence of life on Mars in subsurface and rock interior samples. The package includes instruments to study sample mineralogy (composition, macroscopic and microscopic structural and textural features), organics (elemental, molecular), oxidation state and petrology (major and minor element composition).
The El Laco deposits of northern Chile are the best-preserved volcanic magnetite-apatite ores in the world. The deposits are situated on the flanks of an andesite-rhyodacite volcano at an altitude of 4,700 to 5,300 m. The ores, which are composed mostly of magnetite with minor pyroxene and apatite, occur as massive, tabular bodies, as crosscutting dikes and/or vein complexes, and as stratified, fragmental ores. The El Laco deposit was first described 40 years ago by C. F. Park, who reported iron oxide ore bodies that resembled lava flows, and suggested that the deposit formed as a result of a volatile-rich, iron-rich magma, which intruded the local volcanic sequence at shallow depth and in places erupted to the surface. This interpretation has been assumed by most subsequent investigators. A number of recent reports, however, have suggested that the El Laco deposit is hydrothermal in origin. El Laco is the critical locality for this debate. If El Laco, which is the least altered, best preserved and best exposed deposit of this type, is hydrothermal, then all similar deposits are probably hydrothermal as well. If, however, it can be shown that iron-oxide magmas erupted at even one locality on Earth, then a magmatic origin must be considered for other similar deposits on Earth, and on other planetary bodies. Similarly, if the El Laco ores formed from iron-oxide magmas, there are profound implications not only for the formation of ore deposits, but also for geochemical modeling and textural interpretations of a variety of other volcanic and plutonic rock suites. The laterally extensive iron-oxide deposits on the surface of Mars invite comparison with volcanic iron-oxide ash layers at El Laco, Chile, Durango, Mexico, and Pilot Knob, Missouri.
Recent papers over the last few months have laid to rest previously well accepted evidence for the most ancient fossil life. Detailed geological field and laboratory work has shown that a "BIF" from Greenland containing carbon isotope evidence for life at >3.85 b.y. ago is (a) not a BIF, (b) that the isotope signature is due to contamination, and (c) that the rock is probably not more than 3.65 b.y. old. On the other side of the hemisphere, interpretations of "cyanobacterial" microfossils in 3.45 b.y. cherts from the Pilbara in Australia are untenable because (a) the samples come from a hydrothermal chert vein and (b) the structures appear not to be microfossils. Moreover, there is a certain hypothesis doing the rounds of the conference halls that there was NO LIFE even at 3.5 b.y. I will analyse the arguments in each of these cases and show that there may have been life at 3.75 b.y., and that there was certainly plenty of life (but not cyanobacterial) at 3.5 b.y. from my own work on the Early Archaean cherts of Pilbara and Barberton. In the process, I will cover the criteria for identifying fossil bacteria.
About two dozen meteorites from the Moon have been recognized in the past 20 years. Despite the fact that we have 382 kg of lunar samples from 6 Apollo and 3 Russian Luna missions, the lunar meteorites are providing some important new insights about the geology and geochemistry of the Moon. Although random samples from the lunar surface, they provide a type of ground truth for orbiting remote-sensing missions.
The ring systems of our Solar System abound with examples of places where ring material orbits close to small moons. These types of systems include both the Encke gap in Saturn's A ring as well as all of the narrow ring systems at Saturn, Uranus, and Neptune. These systems are very unlike the equilibrium systems that are typically studied with planetary rings. The main difference is that the particles receive a significant forced eccentricity from the moon at each pass, which gives them sinusoidal streamlines that compress downstream due to shear. I'll show the results of numerical simulations that we have performed of the collisional dynamics of these types of systems. The simulations use local cells with boundary conditions designed for this type of system and particles roughly the same size as what have been measured for the upper end of the size spectrum of Saturn's ring particles. The most significant result we have found is that the evolution of the system is driven by collisions preventing streamlines from shearing through one another. This often produces a negative diffusion like behavior.
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