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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Comets are frozen, largely unaltered reservoirs of dust and gases present in the early solar nebula. They are likely to contain well-preserved records of the chemical, mineralogic, and isotopic character of primordial solar system matter. On January 15, 2006, the Stardust mission returned to Earth with a cargo of particles collected from the coma of comet Wild 2, the first samples of indisputably cometary matter available for laboratory study. Among these investigations, the noble gases provide unique data on contributions to comets from various solar system volatile reservoirs, and of physical processing of gases acquired from these reservoirs. In this talk I discuss the first study of helium and neon in Stardust material, and of the identity of their likely carrier particles, carried out over the past year by workers in four different laboratories.
One of the surprises in samples collected from an icy object forming, and, for most of its lifetime, residing in the cold outer reaches of the solar system was the discovery in other laboratories that many of its constituent particles are igneous, refractory "rocklets" formed at very high temperatures, presumably close to the early Sun, which were then somehow transported to the trans-Neptunian Kuiper belt and incorporated into Wild 2 at about the time of the solar system's birth 4.57 billion years ago. (In retrospect the presence of these "rocklets" wasn't all that astonishing: Ed Ney, Louis Rose and others at Minnesota argued three decades ago from IR spectroscopic data that comets contained igneous grains). A second and completely unanticipated feature of Stardust matter was enormous concentrations of He and Ne that, of known gas acquisition mechanisms, only intense ion irradiation seems able to explain. These two observations, together with isotopic data pointing to Ne similar to that found in primitive meteorites, suggest that gases in Stardust grains were implanted from an ancient, energetic nebular reservoir near the young evolving Sun.
The high temperatures and pressures at the Venus surface result in exotic and possibly vigorous heterogeneous reactions between the atmosphere and surface. Although aqueous processes are absent, this unique geochemistry most likely results in unusual feedbacks between the climate and mineralogy. The sulfur cycle on Venus involves iron minerals, sulfates, the clouds, and the greenhouse effect. Unfortunately, most of this is guess work based on thermodynamics and theoretical models because neither the composition of the lower atmosphere nor the mineralogy of the Venus surface have been determined. I will discuss key measurements that can be made with proven analytical instruments aboard a landed spacecraft. Since there is growing evidence that early sulfur cycles played key roles in the evolution of the inner planets, these investigations have important implications for understanding both early Mars and the Hadean.
VV Cephei is a binary system containing a red supergiant star with a strong stellar wind and a hotter, smaller companion. When the hot companion goes into and comes out of eclipse behind the cool star, its orbital motion and the resultant changing absorption provides us with a probe of the spatial structure of the wind. Recent reanalysis of data obtained by the Space Telescope Imaging Spectrograph has resolved the spatial extent of the extended cool-star atmosphere.
A petrogenetic model of magma genesis and low shield evolution is developed by comparing volcanoes at or near Tempe Terra, Pavonis Mons, Syria Planum, and the type area for plains-style volcanism, the eastern Snake River Plain (ESRP) of Idaho. Constraints are derived from surface geomorphology, dimensional topography, geologic settings, age relations, and geochemical and isotopic systematics of ESRP basalts. Petrologic studies of basaltic shergottites provide constraints for magma genesis on Mars. Trace element trends reflect variable mixing between enriched and depleted (or primitive) components in source regions, and each shield is derived from a separate magma batch. A well-constrained model for ESRP basalts is thus believed to be applicable to the petrogenesis of low shields on Mars. Low-volume magma batches, generated in a thermally-weakened lithospheric source (near- or post-plume), intrude into the crust and evolve to produce cumulate piles with late-stage trapped liquids. Successive primary magmas intrude and mix with the layered precursors, becoming variably enriched in trace elements and volatiles. Tests for geochemical enrichment and variability in low shields on Mars could be used to confirm or deny this hypothesis.
The relatively cool, dense atmospheres of substellar objects - gas giant planets, brown dwarfs, and extrasolar giant planets - are ideal environments for the formation of molecules and condensates and the establishment of equilibrium chemistry. For this reason, thermochemical models have been essential for understanding and guiding astronomic observations of substellar atmospheres. Recent applications include updated constraints on the atmospheric water abundances of Jupiter and Saturn. Thermochemical models of extrasolar planets and brown dwarfs have also been used to identify important gases and clouds which may be diagnostic of atmospheric pressure, temperature, or weather.
Mare basalts cover ~17% of the lunar surface, and represent flows that filled the large basins formed by earlier bolide impacts. Most of these maria are found within the great basins on the nearside with a few others filling smaller basins in the farside. Mare volcanism is the continuous expression of mantle evolution after differentiation and formation of the lunar crust. With the Apollo and Luna samples, it was generally thought that volcanism occurred during a period of ~700 Ma, from ~3.85 (and a less clear age of ~4.2 Ga) to ~3.15 Ga. With the advent of new lunar remote sensing data (surface chemical composition), new work with older data from the Orbiter I-IV images (crater counting statistics) and the finding of new lunar mare basalt meteorites (presently a total of 10), much progress has been achieved regarding the complex composition and geological evolution of the Moon. Currently, based on new age determination of lunar mare basalts, it is believed that lunar volcanism extended over a longer period of about 1.5 Ga: between 4.3 Ga (Kalahari 009) and 2.8 Ga (NWA032/479). Based on remote sensing data, mare volcanism should have occurred to even more recent times, ~1.2 Ga.
In this seminar, it will be presented recent Ar-Ar age determination for lunar mare meteorites, which in most cases are comparable to other isotopic systematics. In those cases Ar-Ar results are not comparable, it is still possible to learn more about the history of the meteorite being studied and ultimately about the geological history of the Moon.
How did the planets form? How can the Moon tell us about these events? Research scientist Dr. Bill Bottke discusses recent advances in our understanding of planet formation that are challenging long-held views, with the strongest models suggesting that several planets did not form where we see them today!
The terrestrial and lunar cratering rate is often assumed to have been nearly constant over the last 3 Gy. Different lines of evidence, however, suggest the impact flux from kilometer-sized bodies increased by at least a factor of 2 over the last ~100 My. Here we report that this apparent surge was triggered by the catastrophic disruption of the Baptistina parent body, a ~170 km diameter carbonaceous chondrite-like asteroid that broke up 160 +/ 20 My ago in the inner main belt. Numerous fragments produced by the collision were slowly delivered by dynamical processes to orbits where they could strike the terrestrial planets. Using numerical simulations to model this asteroid shower, we find it is the most likely source (>90% probability) of the Chicxulub impactor that produced the Cretaceous-Tertiary (K/T) mass extinction event 65 My ago.
Viscosity of silicate melts is of fundamental importance in understanding volcanic and magmatic processes in Earth. A new empirical viscosity model for natural anhydrous and hydrous silicate melts was developed, accounting for the dependence on temperature and melt composition (including water content). This model with 37 fitted parameters can fit the entire high- and low-temperature viscosity database (1451 data points) of all “natural” silicate melts with 0.61 logn units in terms of 2 sigma deviation. This general model can be applied to calculate viscosity for modeling magma chamber processes and volcanic eruptions. It can also be used to estimate glass transition temperature and cooling rate of natural silicate melts.
Because the pressure dependence of hydrous melt viscosity at low temperature is not known, new research was carried out to investigate the pressure effect on hydrous melt viscosity. First, the speciation of dissolved H2O in rhyolitic melts with 0.8 – 4 wt% water under pressure 0.94 – 2.83 GPa was determined. These data are critical for viscosity inference using a newly developed hydrous species reaction viscometer. The new viscometry has been extended to hydrous rhyolitic melts with 0.8 - 4 wt% water for the first time in the high viscosity range and high pressure, up to 2.8 GPa. Besides this new method, a parallel plate viscometer in an internally-heated pressure vessel was used to measure the viscosity of rhyolitic melts containing 0.13 and 0.8 wt% water at 0.2 and 0.4 GPa. Combined with literature data, a model was developed to accommodate the effect of pressure, temperature and water content on the viscosity of rhyolitic melt in the high viscosity range. The results show the dependence of viscosity on pressure is complicated but relatively weak.
The dramatic contrast between the basalt-filled lunar nearside and the cratered uplands has been attributed to either asymmetric accretion or relaxed scars from the Procellarum impact basin. A new model considers the effect of the farside South-Pole-Aitken Basin (SPAB) on massive crustal failure on the lunar nearside. In this model, an oblique trajectory resulted in convergence of shock rarefactions antipodal (but offset) from the SPAB. As a result, deep-seated conduits controlled subsequent massive mare flooding during the Imbrian Period and structural control of recent out-gassing (e.g., Ina).
Structural geological mapping of Meteor Crater, Arizona, and Lonar Crater, India, illustrates how target rocks respond to and are deformed by meteorite impacts. As the target rocks for these impact events are sedimentary rocks and basalt, respectively, the impact craters are good analogs for simple craters produced on Mars. Impact deformational features exposed on the crater walls can be distinguished from preexisting tectonic deformational features present in the target rocks. Interestingly, Meteor Crater provides an excellent opportunity to study the mechanics of impact cratering processes in a fractured rock medium. In addition, we will show how impact fracture and fault systems exposed on crater walls contributed to the formation of gully erosional features. These provide new insights for gully formation on Mars.
Mt. Tsaratanana, the highest peak in north-central Madagascar (approximately 2876 m), is one of several Cenozoic eruptive centers that extend from the Seychelles south to the Comores Islands. Miocene volcanism (approximately 10 Ma) is of peraluminous type and consists of less abundant basanitic flows and more abundant phonolitic and trachytic tuffs and flows. A similar volcanic assemblage can be found in Cameroon within the Cameroon volcanic line. Linear Anorthosite bodies of highly differentiated melts occur within the Grenville province of Quebec. The spatial and temporal distribution of the three mentioned areas, together with the whole rock composition and the complex mineral zonation with large compositional amplitudes and dissolution textures is taken as evidence of crystal movement within the magma chamber and across compositional boundaries between magma batches. A multiple "step-cycle" model, involving growth and transport of a crystal into another magma batch and its return to the original host magma is suggested by obtained data. The implication of the model in our understanding of terrestrial planets and their moons will be discussed.
Large igneous provinces (LIPs) are formed by eruption of large volumes of basaltic magma (> 1million km2) over geologically short timescales (typically less than 10 million years). The defining feature of LIPs is that they are not associated with normal plate tectonic magmatism, rather they are thought to be associated with the initiation of mantle plumes or other non-tectonic processes. LIPs have also been identified on the Moon, Mars, and Venus, suggesting that they may represent the dominant form of volcanism in the solar system. The Ontong Java Plateau (OJP) and the Hawaiian Ridge-Emperor Seamount Chain (HR–ESC) are two of the largest LIPs on Earth. The OJP is Earth’s largest known igneous event, covering an area roughly the same size as western Europe in the southwest Pacific Ocean, while the HR–ESC is the longest oceanic island chain on Earth. Sample recovery from each is costly and difficult, with the end result being that significant portions of both are either completely unknown or poorly characterized. Recent deep sea drilling expeditions have returned basement samples from these regions; my talk will discuss two projects that focus on the geochemistry and petrology of these samples.
Ca-rich plagioclase is commonly found in island arc basalt at volcanic front. It is well-known that composition of plagioclase becomes enriched in Ca with increasing H2O content in melt. Therefore, Ca-rich plagioclase suggests H2O -rich island arc basalt at volcanic front. In order to confirm H2O-rich nature of frontal arc magmas, I am analyzing trace quantities of H2O in Ca-rich plagioclase, using polarized infrared spectra. Analytical results clearly demonstrate that H2O content in plagioclase becomes higher with increasing An content. The estimated H2O content in melt changes widely from 3 to 6 wt%.
Mass transport in the upper mantles of Earth and other terrestrial planets occurs mostly by the solid-state deformation of rocks composed predominantly of olivine, pyroxene and garnet/spinel. As olivine is volumetrically the most abundant mineral and is likely the weakest major mineral, this transport can generally be well modeled by the creep behavior of olivine aggregates. In the lithospheric upper mantle, deformation of olivine will occur within the power-law breakdown (dislocation glide) and dislocation creep regimes. Asthenospheric and deeper mantle flow will occur predominantly in the dislocation creep regime, but may also involve diffusional creep processes. In all of these regimes the mechanical behavior of natural iron-bearing olivine will be influenced by the thermochemical environment, so that not only temperature and pressure, but also oxygen fugacity, water fugacity and silica activity will be important. As I will discuss, careful consideration of the importance of the thermodynamic environment can lead to better constraints on flow laws, which differ in important ways from those currently used by geodynamicists.
Regional GPS velocities from Luzon, Philippines, combined with focal mechanism data from the Harvard Centroid Moment Tensor (CMT) Catalog, are used to constrain tectonic deformation in the complex plate boundary zone between the Philippine Sea Plate and the Sundaland Block (part of Eurasia). These datasets are inverted simultaneously to estimate plate rotations and fault-locking parameters for the tectonic blocks and faults comprising Luzon. Best-fit models suggest that much of the Philippine Fault and its associated splays are locked to partly coupled, while the Manila and Philippine trenches appear to be poorly coupled. The Philippine Fault and associated intra-arc faults accommodate much of the trench-parallel component of relative plate motion. The resulting elastic block models are also used to inspect active tectonics and magmatism within the Macolod Corridor (location of the Taal Caldera) a geologically complex area in southwestern Luzon, characterized by extensive volcanism, crustal thinning, and widespread faulting. We then focus on deformation patterns associated with magmatic activity at Taal Volcano, an active tholeiitic volcano located within the Taal caldera. Elastic models are compared with elastic-viscoelastic models of deformation observed by GPS on and near the volcano. Finite element models (FEM) of volcanic deformation using axisymmetric geometry are utilized to define a centrally located small spherical magma source within an elastic half space. Models are then tested using concentric viscoelastic shells, embedded in multi-layered elastic half-space (approximating actual crustal rheology in the area). Using variable pressure histories as input, a series of forward models are then fit to the time history of continuously observed GPS deformation for the baseline defined by continuous GPS stations on volcano island. Viscoelastic models allow for simpler pressure histories and require significantly reduced overall pressure estimates, compared to purely elastic models.
Elemental concentrations (Mars Odyssey Gamma-Ray Spectrometry) and mineralogy (Mars Global Surveyor Thermal Emission Spectrometry) show that the Martian surface contains compositionally distinct regions. Some units correspond to mapped geologic units, while others do not. Multivariate cluster analysis using both datasets indicates that mineral abundance is not always correlated with chemical composition.
Models of lithospheric deformation tie observed field measurements of gravity and topography with surface observations of tectonic features and provide critical insight into the physical mechanisms responsible for such tectonic features. We systematically model the sources of stress within the lithosphere of Mars, and compare and score these stress models directly with surface observations of faults mapped to-date.
Thermodynamic modeling may be utilized to predict the compositions and densities of partial melts produced under specified temperature and pressure conditions for model mantle bulk compositions of the terrestrial planets. Effects of variable bulk composition, oxygen fugacity, and the dynamics of the melting regime can be explored with this technique. Model construction will be reviewed and a new phase equilibrium algorithm (xMELTS) will be discussed. Decompression melting scenarios for the Earth and Mars will be compared, with emphasis on solid-solid phase transitions and their effect on melt productivity.
The vast majority of ice on Mars today resides at the poles. Recent spacecraft data have revealed evidence for non-polar deposits that range from tropical mountain glaciers, mid-latitude valley glaciers and glacial land systems, to high-latitude ice-rich mantles. Together, these deposits are testimony to significant variations in the complex Amazonian climate history of Mars. These deposits provide geologic evidence to help deconvolve the history of spin-axis/orbital parameter variations of Mars during the Amazonian.
Global mapping by the visible and near-infrared imaging spectrometer OMEGA aboard ESA/Mars Express has discovered unique deposits of phyllosilicates minerals widespread across the planet [Poulet et al. 2005]. The presence of these minerals on Mars is of great exobiological relevance, because (1) the formation of these hydrous minerals requires moderate to high pH and high water activity, (2) some of phyllosilicates are potential prebiotic catalyst. Here, we first reassess the detection of these minerals at the light of the analysis of new OMEGA data as well as NASA/MRO/CRISM data acquired since the publications of 2005. We emphasize the spectral diversity of each major class of phyllosilicates. While the Fe, Mg and Al-bearing smectites are the most common, kaolinite and chlorite are also potential spectral matches of some phyllosilicate-rich occurrences. New OMEGA observations consistently indicate the presence of phyllosilicates in deposits that are in place, rocky units (outcrops, scarps and crater ejecta) of ongoing erosion in Noachian terrains. The absence of phyllosilicates in younger deposits confirms that environments suitable for phyllosilicate formation have not been present at or near the surface since the Noachian. We then provide quantitative analysis of the surface spectra using nonlinear spectral mixing  in order to determine the modal mineralogy (mineral abundances) of some phyllosilicate-rich outcrops. Different processes of formation will be then discussed.
The steady improvement in the resolution and precision of imaging and topographic data for the terrestrial planets has created an increased need for field topographic measurements of a variety of landforms. Differential Global Positioning System (DGPS) data have proved to be quite useful in obtaining precise information about the shape and relief of landforms such as lava flows, sand dunes, and paleo-shorelines. This seminar will review how DGPS data are collected and documented for such features, supplemented by other techniques for obtaining detailed topography along short (<10 m) transects, and their potential for improving geologic interpretations of spacecraft data.
Pallasites are stony-iron meteorites consisting predominantly of two phases, olivine and metal. Phosphoran olivine is a rare phase found in five Main Group pallasites as partial overgrowths or rims on phosphorus-free olivine. Its occurrence requires explanation if pallasite formation is to be understood. Both dynamic crystallization and isothermal experiments were conducted to investigate the formation of phosphoran olivine. Pallasites have long been thought to form by mixing of core metal and mantle olivine following extensive differentiation. However, mixing models fail to account for several features of pallasites. A new conceptual model called inefficient differentiation interprets the pallasites as metal and olivine residues following the melting and extraction of basaltic melt from a chondritic precursor. Details of this new model will be explored.
The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, developed under NASA’s Discovery Program, will be the first probe to orbit the planet Mercury in March 2011. Launched in August 2004, MESSENGER successfully completed the first of three flybys of Mercury in January 2008. The Mercury Dual Imaging System acquired an 11-color mosaic of part of the hemisphere not seen by Mariner 10, including the entire Caloris basin; several large monochrome mosaics at a range of resolutions; a series of color frames designed for photometric analysis; and inbound and outbound movies. The Mercury Atmospheric and Surface Composition Spectrometer obtained the first high-resolution spectral reflectance measurements (at ultraviolet to near-infrared wavelengths) of surface composition, conducted limb scans of exospheric species, and mapped the structure of the neutral sodium tail. The Magnetometer measured Mercury’s internal field at low latitudes and documented the major plasma boundaries of Mercury’s magnetosphere. The Energetic Particle and Plasma Spectrometer made the first measurements of low-energy ions in Mercury’s magnetosphere. The Mercury Laser Altimeter carried out the first space altimetric profile of the planet. Other instruments in the payload provided baseline measurements that will aid in the interpretation of data from the mission orbital phase. Together, the MESSENGER flyby observations have begun to advance our understanding of the innermost planet and, more generally, of the family of inner planets.
The highly siderophile elements (HSE: including Re, Os, Ir, Ru, Pt, Rh, Pd and Au) are geochemically characterized as having a strong tendency to partition into metal relative to silicates. Results of experimental studies of HSE behavior conducted at relatively low pressures consistently show liquid metal/liquid silicate concentration ratios (D values) of 104 or greater. Despite this, the abundances of the HSE in the terrestrial mantle are at the low ng/g level, only ~200 times lower than bulk chondritic meteorites. Thus, it has been recognized since the 1960’s that the concentrations of these elements in the mantle are substantially higher than would have resulted from metal-silicate partitioning at relatively low pressures, as might be expected if the Earth formed via accretion of smaller bodies including planetary embryos that had segregated distinct cores prior to their addition to the growing proto Earth. This observation has led to the development and testing of numerous hypotheses to explain the apparent discrepancy. They can be reduced to three broad categories of hypothesis: 1) greatly lowered metal-silicate D values resulting from either composition effects, such as high S content in the segregating metal, or raised temperatures and pressures, such as would be found at the base of a deep magma ocean, 2) incomplete core separation during which some HSE-bearing metal is retained in the silicate Earth, and 3) late accretion, normally defined as continued accretion to Earth of materials with chondritic abundances of the HSE, subsequent to the termination of substantial transport of HSE into the core. The dominance of one of these processes relative to the others might have resulted in a characteristic geochemical signature that could ultimately permit discrimination. Confirmation of one of these processes as the primary control on the HSE abundances present in the mantle would be a major advance in understanding early solar system and early Earth processes. I will review the latest HSE abundance data, together with HSE experimental data that relate to these hypotheses. Each hypothesis has strengths. Each hypothesis also has serious weaknesses. This is not a new conclusion, but as the database grows for these elements, the weaknesses become more troubling and may ultimately require reconsideration of these hypotheses.
Because its axis of rotation is nearly perpendicular to the ecliptic plane, the poles of the Moon contain areas that are permanently dark and other areas the may be nearly constantly illuminated. This simple relationship has profound consequences; the lunar poles are a unique environment, containing deposits, displaying processes and having a history and evolution very different from the rest of the Moon. The dark regions may be as cold as 50–70 K. Cometary debris and meteorites containing water-bearing minerals constantly hit the Moon. Most of this water is lost to space, but if a water molecule finds its way into a cold trap, it is there forever – no physical process is known that can remove it. Over geological time, significant quantities of water could accumulate. Measurements by the Clementine and Lunar Prospector spacecraft showed that volatile deposits, possibly in the form of water ice, exist near the lunar poles. Additionally, both poles show small areas that appear to be in sun illumination for periods significantly greater than one-half of the 708-hour lunar day. Mini-SAR is a guest payload on India’s Chandrayaan-1 mission to the Moon, scheduled to be launched later this year. This 550 kg spacecraft will enter a polar orbit and map the Moon for 2 years. The Mini-SAR instrument will map both poles and obtain detailed information on the surface scattering properties of permanently dark areas. Analysis of these data will permit us to identify materials in the dark areas with scattering properties consistent with water ice. The poles of the Moon are of great interest and value from both a scientific and an operational perspective. Scientifically, the poles offer us new processes to study and an untold story to recover. The permanent darkness and quasi-permanent sunlit areas offer resources and enable continuous human presence on the Moon. Because of discoveries made about the poles, the Moon has become more complex and mysterious in the last decade. The next decade of exploration may uncover new secrets and clues to the history of the Solar System.
In its four years orbiting Saturn, Cassini-Huygens has revealed both Titan and Enceladus to be complex, active worlds that might well harbor life or the chemical clues to how life began on Earth. Titan, as well, has a methane cycle much akin to Earth's water cycle. Both objects are worthy targets for future exploration.
Thermodynamic analyses of saline minerals exposed at the martian surface indicate that the last ~3.5 Ga of martian history presented significant challenges for the emergence and evolution of life. On Mars, the window of habitability was fleeting; largely occurring during Mars’ planetary infancy. However, the identification of clay minerals in some of the oldest martian lithologies suggests distinctly different chemical conditions than those implied by the presence of salt assemblages. At present, the chemical conditions needed to form and stabilize clay minerals on Mars are only qualitatively understood. New laboratory studies on the synthesis of martian clay minerals shed new light on the earliest chemical conditions of the surface and contribute to a broader picture of the geochemical evolution of Mars. Using more detailed and quantitative knowledge on the stability of saline minerals and clays on Mars, constraints can begin to be placed on the habitability of the ancient surface as well as the prospects for the origin and evolution of life on our planetary neighbor.
Because science is a reductionist enterprise, categorization is an important and productive scientific tool; it is employed in many branches of science. Planetary science today faces a significant categorization challenge—i.e., defining what objects are and are not planets. This challenge has come to the fore in part owing to the discovery of numerous “ice dwarfs” (Stern 1991) in the outer solar system (Jewitt & Luu 1992), the recognition that Ceres is a dwarf planet (a fundamentally different body than the smaller asteroids; Thomas 2004), the discovery of pulsar planets around compact stellar remnants (Wolszczan & Frail 1992), and the numerous discoveries of hot Jupiters near other stars (e.g., Charbonneau 2003). Also factoring into this is the controversial planet definition adopted by astronomers in the International Astronomical Union. I argue that what one desires in a comprehensive planetary definition is a self-consistent, “sieve” algorithm that allows one to reliably and consistently sort objects into “planetary” and other categories. The geophysical planetary definition (GPD) is once such a sieve, which I shall describe. The GPD defines planets as natural objects in space that are massive enough for gravity to make them approximately spherical but not so massive that they have generated energy by internal nuclear fusion. The GPD nicely separates planets from both smaller bodies that “do not know they are large” by dint of reaching hydrostatic equilibrium, and larger bodies that manifest themselves as brown dwarfs and stars, and allows bodies to be reliably categorized based on a single, simple, robust observable property—their known or estimated mass. The GPD avoids the severe difficulties associated with dynamical definitions (which result in identical objects being classified differently depending on their dynamical circumstance), origin-based definitions (because we cannot through remote sensing uniquely determine an object’s mode of origin), and attribute-based (e.g., the presence of an atmosphere or satellites or oceans, each of which are problematic to determine observationally and each of which rule out various objects commonly regarded as textbook examples of planets in our solar system). Furthermore, the GPD does not bias the population of planets in planetary system based on non-scientific biases such as preference for a limited number of planets in our solar system. This talk is intended to provoke discussion.
A series of experiments were conducted to study mineral catalyzed carbon reduction processes in subseafloor hydrothermal systems. In experiments involving magnetite and CO2 and H2-bearing aqueous fluids at 400oC and 500 bars, time-series fluid samples indicated significant concentrations of dissolved CO and C1-C3 hydrocarbons and relatively large changes in dissolved CO2 and H2 concentrations, consistent with formation of additional hydrocarbons beyond C3. The isotope results showed a pattern of C and H isotope enrichment between C1 and higher hydrocarbons. The “isotopic reversal” trend was not observed for 13C values of dissolved alkanes with increasing carbon number. This may relate to the specific mechanism of carbon reduction under hydrothermal conditions at elevated temperatures and pressures. In another experiment, the catalytic role of iron-nickel sulfide (Pentlandite) was evaluated using a 13C-labeled carbon source at conditions (T, P, and fluid chemistry) close to Rainbow/Logatchev vent systems. Dissolved 13C-bearing alkane species were produced with relatively low H2(aq)/CO2(aq) ratio and the existence of dissolved H2S. Hydroxymethylene is the key intermediate in the hypothesized reaction mechanism, which was consistent with XPS and ToF-SIMS analysis results on the mineral product.
For the past several years there have been two sounding radars in orbit around Mars. One is MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) on the Mars Express orbiter and the other is SHARAD (Shallow Radar) on the Mars Reconnaissance Orbiter. SHARAD is designed to study dielectric contrasts associated with geologic layering on fine (10 m) vertical scales and to typically sub-km depths. SHARAD complements the spatially coarse but deeper sounding of the lower-frequency MARSIS. The depth of exploration of these radars is controlled by the loss properties of the material that the radar waves pass through, with the result that ice-rich material is the most fruitful target for the radars. The radars have mapped the internal structure of the layered deposits at both poles, revealing details of the layering not observable from surface exposures. This includes two vertical scales of reflection spacing, which suggest the involvement of two different periodicities of climate forcing. The radars show that the layered deposits are dominated by ice. An unexpected result is that the substrates beneath deflect very little in response to these loads. This implies that the elastic lithosphere at the poles is very thick, or the load is not in equilibrium with the viscous mantle, or that martian heat flow has significant spatial variations. The radars have also mapped reflections in other areas of Mars, including many locales in the northern lowlands.
(1) A review of what the lunar knowledge base consisted of prior to the Apollo missions; (2) How the gained Apollo knowledge influenced interpretations of Mars images; And (3) how these were revised after comparisons with features of the wind-blown eastern Sahara of North Africa, the driest place on Earth.
Many of our colleagues in the 1960s, Shoemaker, Wilhelms, Mursurky, Urey, Hess, Wasserburg, and the like had reasoned that exploration of the Moon would provide insights into the history of the solar system and the sun as well as the Moon itself. What none of us fully comprehended, however, turned out to be just how many unanticipated questions about the Earth would be stimulated as we gained increasingly detailed knowledge about the Moon - first through analysis of samples and geophysical data from Apollo missions and then from subsequent remote sensing missions that continue to build on the Apollo science foundations.
The first European planetary mission, Mars Express, was launched in June 2003 and has been orbiting the red planet for about four and half years, providing fantastic data on the surface, subsurface, atmosphere and space environment of Mars. While focusing on global studies, the unifying theme of the mission is the search for water in its various states everywhere on the planet. A summary of scientific results from all experiments onboard will be given. Mars Express is paving the way for the second European mission to Mars, ExoMars, which will be the first in ESA’s new Exploration Programme and will focus on finding traces of past or present biological activity underneath the surface. The MarsNEXT mission is being proposed as the following step consisting of a network of three surface stations complemented by an orbiter to focus on the internal structure, atmospheric dynamics and geology of each landing site. This mission will also demonstrate key technologies to prepare for the long-term goal of Mars sample return in which Europe will play a significantly large role.
This talk mainly addresses TEM equipped with a Gatan Image Filter (GIF) as a powerful tool in mineralogy field to examine crystal structures, analyze chemical compositions, and probe the elemental valence state on a nanometer scale. Chemical and structural variations at deformation twinning boundaries in pyroxene minerals, mineral constituents of quartz sand coatings in aquifer environment, and quantification methods using electron energy loss spectroscopy (EELS) for determination of manganese valence will be detailed.
The successful Mars missions of the last decade have provided new data for models of the composition of the Marian crust and its chemical evolution. The bulk chemistry of upper crust has been estimated using selected soil analyses and orbital data has shown subtle variations in crustal composition over time. Also, results from the Gamma-Ray Spectrometer (GRS) aboard the Mars Odyssey spacecraft are used to construct models of present and past Martian crustal heat flow.
Cometary nuclei are considered to be the most pristine objects of the solar system and as a consequence, their study gives essential information on the processes at the origin of the solar system. These bodies have been shown to have a very low density and high porosity. The properties of the dust ejected by comets confirm the global characteristics of the cometary nuclei. Comparison of the scattered light measurements with numerical simulations give an estimation of the silicates over organics mass ratio, as well as a size distribution of the dust particles suggesting that a significant part of the ejected particles are aggregates of submicron grains  which was recently confirmed by the results of the Stardust sample mission (showing fluffy structures for very large particles; up to 100 m) . Cometesimal aggregation simulations taking into account the evolution of the cohesive energy by sintering processes during accretion in the Kuiper belt can be used to interpret the layered structure and surface features observed for previous comets  and quantify the tensile strengths of these objects. To describe the more recent evolution of these objects, thermal evolution models of comet nuclei have been rather successful in explaining global aspects of comet observations. A new quasi-3D approach for non-spherically shaped comet nuclei has been developed for the case of 67P/Churyumov-Gerasimenko nucleus to analyze the effect of the irregular shapes (non-spherical shapes, mountain-like and crater-like features) on its thermal evolution, on the local crust formation and the onset of its activity. Our simulations suggest that depressions on the surface play a role in the internal stratification of the nucleus and can disappear in a comet’s lifetime . The results of such simulations can be used to derive generic cometary nuclei models to be implemented in the results analyzes of the CONSERT experiment on-board the Rosetta mission that will constrain the internal dielectric properties and inhomogeneities of the nucleus by radio wave transmission . While it is now established that cometary nuclei are very porous and fragile objects, it will then be possible to better constrain their formation processes and later evolution.
The role of fluids in the reequilibration of minerals and rocks is fundamental to understanding the mechanisms and kinetics of metamorphic and metasomatic processes. Data for the solubility of minerals in aqueous solutions at high pressures are essential for our understanding of fluid properties, mass transport and growth/dissolution processes of minerals in Earth’s crust and upper mantle.
Drilling allows obtaining information on the subsurface structure of impact craters, provides ground-truth for geophysical studies, and delivers samples of rock types not exposed at the surface. Recently the International Continental Scientific Drilling Program (ICDP) has supported projects to study impact craters. The first ICDP study of an impact structure was at the subsurface Chicxulub impact crater, Mexico, from late 2001, which reached a depth of 1511 m and intersected 100 m of impact melt breccia and suevite. Between June and October 2004, the 10.5 km Bosumtwi crater, Ghana, has been drilled with ICDP support. It is a well-preserved complex impact structure with a pronounced rim and is almost completely filled by the 8 km diameter Lake Bosumtwi, which is a closed-basin lake that has wide paleoclimatic significance and a detailed paleo-environmental record. In terms of impact studies, Bosumtwi is the best preserved young complex craters known, and is the source crater of the Ivory Coast tektites. Drilling also allows correlating all the geophysical studies and provides material for geochemical and petrographic correlation studies between basement rocks and crater fill in comparison with tektites and ejected material. Sixteen different cores were drilled at six locations within the lake, to a maximum depth of 540 m. Borehole logging as well as vertical seismic profiling (to obtain 3D images of the crater subsurface) were done in the two deep boreholes. About 2.2 km of core material was obtained. This includes ca. 1.8 km of lake sediments and 0.4 km of impactites and fractured crater basement (in the deep crater moat, and on the central uplift). Analyses of samples and geophysical data published in 2007 by several different research groups.
The Cassini spacecraft has returned images of Saturnian satellites from Phoebe inward to the “ring moons”. Crater counts on these bodies are providing clues about the origin and time histories of the impacting populations. Iapetus has a dozen or more basins, while only a few basins have been found on all the moons interior to Titan’s orbit. Enceladus displays an enormous range of crater-retention ages. Hyperion and Phoebe have “shallow” (top-heavy) crater size distributions. Titan has been resurfaced within the last billion years at minimum. Present-day impacts on the satellites are dominated by “comets”, except for the numerous distant irregular satellites like Phoebe, which strike each other. I will present model ages of satellite terrains for different assumptions about the time history of the impact flux, including one based upon a Solar System-wide cataclysm 3.9 Ga in the context of the “Nice model”. Some very heavily cratered terrains may reflect this event, rather than bombardment shortly after satellite formation some 4.4-4.5 Ga.
Synchrotron x-ray computed microtomography (XMT) can be used to generate high resolution three-dimensional (3D) volumetric representations of chondritic meteorites. To examine the role of impacts in the evolution of asteroids as seen through their chondritic offspring, we have performed a quantitative 3D study of metal grains in a suite of increasingly shocked L chondrites with XMT. Our data allow rigorous quantification of size number distributions and collective morphology of Fe(Ni) metal phases in chondritic meteorites. At the resolution of our XMT measurements (8.4–17.9 μm/voxel), the number of metal particles increase with higher degrees of petrographically identified shock loading, indicating a coalescing of Fe–Ni metal at or below this scale. Additionally, our results demonstrate that collective degrees of metal grain preferred orientation increase with greater degrees of impact-related compaction and shock loading. Ductile metal grains in L chondrites collectively begin to demonstrate whole rock foliation at peak shock pressures <5 GPa, pressures great enough to compact and indurate loosely bound chondritic material, and our results constitute evidence for multiple generations of impact events acting on the L parent body or bodies. Additionally, results and the implications of investigations of the nature of pore spaces in uncompacted ordinary chondrites will be discussed.
The Moon and all the terrestrial planets were resurfaced during a period of intense impact cratering that occurred between the time of their accretion, ~4.5 billion years ago, and ~3.85 billion years ago: the crater record and radiometric dating of lunar rocks attests to this conclusion. However, identifying the source(s) of those planetary impactors has proven elusive; speculations have included comets, asteroids, and fragments of a shattered 'large planetesimal'. I will describe compelling evidence that the source of the impactors was the main asteroid belt, and that the dynamical mechanism that caused the so-called 'Late Heavy bombardment' ~3.9 billion years ago was unique in the history of the Solar System and distinct from the processes producing the flux of objects that currently hit planetary surfaces. The Late Heavy Bombardment was a rain of asteroids dynamically ejected from the main asteroid belt, possibly due to the effects of orbital migration of Jupiter and Saturn.
Among all seven nakhlites five have been dated by 39Ar-40Ar at NASA-JSC. The ages of all the nakhlites are similar at ~1.2-1.4 Ga. Also, an isochron of total 40Ar versus total K for six nakhlites gives an age of 1325±18 Ma suggesting a common formation age for nakhlites. Unlike nakhlites, Ar-Ar ages of shergottites are strongly affected by excess 40Ar through all gas extractions and show older radiometric ages by other techniques. For example, Zagami contains excess 40Ar relative to its formation age of ~170 Ma as determined by the Sm-Nd method. 39Ar-40Ar analyses of separated plagioclase and pyroxene samples have been investigated to understand the origin of this excess 40Ar. All the separated martian samples show similar concentrations of excess 40Ar, ~1x10-6 cm3STP/g. Bulk and mineral separated samples of other shergottites also give concentrations of excess 40Ar ~1-2x10-6 cm3 STP/g, in spite of a variation in K content. This excess 40Ar was inherited from the shergottites’ magma, either by degassing of a larger volume of material or by early assimilation of old K-rich crustal material.
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