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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We report on a petrologic study of 27 KREEP basalt fragments in six thin sections of samples collected from Apollo 15 stations 2, 9A, 6A, and 7. On the basis of sampling site, local stratigraphy, and regional remote sensing data, the samples represent KREEP basalt lava flows emplaced locally (ending up beneath the younger Apollo 15 mare basalts) and others emplaced north of the Apollo 15 site and deposited at the site as ejecta from the large craters Aristillus and Autolycus. KREEP basalts in this igneous province have a volume of 103–104 km3. Mineral and bulk compositional data indicate that the erupted magmas had Mg# [100 x molar Mg/(Mg+Fe)] up to 73, corresponding to orthopyroxene-rich source regions with Mg# >80. Minor element variations in the parent magmas of the KREEP basalts, as inferred from compositions of the most magnesian pyroxene and most calcic plagioclase in each sample, indicate small but significant differences in the concentrations of minor elements and Mg#. These differences suggest variations in the compositions of lower crustal or mantle source regions and different amounts of partial melting to produce the KREEP basalts. The Hadley-Apennine KREEP basalt province was active between 4.3 to 3.84 Ga, but the scarcity of age data does not allow us to determine if the magmatism was concentrated at the extremes of this range or occurred sporadically during this interval. Formation of the youngest basalts may have been triggered by formation of the Imbrium basin, but the existence of older KREEP basalt magmas (if verified) suggests a role for earlier large impacts as well.
The issue of the duration of Martian magmatic activity is one the controversial debates recently. The young radiometric ages of ~180 Ma for shergottites, a class of Martian meteorites, reflect the timing of crystallization from a magma or rather later events related to shock metamorphism or fluid infiltration. Shock-recovery and annealing experiments were undertaken to understand shock effects on U–Pb isotope systematics of baddeleyite. Shock pressures up to 57 GPa and annealing up to a partial-melting temperature of ~1300 ºC did not cause phase transition from monoclinic baddeleyite structure to high-pressure/temperature polymorphs of ZrO2. These results are consistent with the crystal structures of baddeleyite in basaltic shergottites. The U–Pb systems of baddeleyite did not show any remarkable isotopic disturbance, implying that the U–Pb isotopic systematics of baddeleyite is durable for shock metamorphism. Our experimental results suggest that the U–Pb ages of baddeleyite in shergottites will give crystallization ages of Martian volcanic rocks. We also have undertaken U–Pb isotopic studies on baddeleyite in the Roberts Massif (RBT) 04261 shergottite. Baddeleyite in RBT 04261 is usually associated with ilmenite and shows monoclinic structure, suggesting to have formed by crystallization from a residual liquid and not by shock metamorphism. In situ U-Pb isotopic analysis of baddeleyite yields a concordant age of ~200 Ma. Since the U–Pb system of baddeleyite is considered to be more resistant to resetting during reheating events, and olivine in RBT 04261 preserves an igneous calcium zoning, the young age of baddeleyite could be interpreted as a crystallization age of RBT 04261. The present results imply that Martian magma was still forming only 200 Ma, and that Mars has been geologically active until the recent past.
Icy satellites provide a unique vantage point for understanding geophysical processes in the Solar System. On these bodies, the same physical processes that guide our understanding of terrestrial planets must be applied to a unique material (water ice) in a unique environment (the cold outer Solar System). I present results from a long-term campaign to model and understand the detailed mechanical deformation of ice lithospheres. Through such modeling we gain greater insight into the origin of the tectonic deformation observed on icy satellites and constrain the thermal and physical conditions present on the satellite at the time such features formed. Understanding the mechanisms that have created the unique surface features observed on icy satellites therefore constrains their plausible thermal evolution.
It was one giant leap for mankind, and it was witnessed live by more than six hundred million people worldwide. The Apollo 11 television signal from the Moon was received at stations in California and Australia. From there, the picture was converted to commercial TV standards for worldwide distribution. This conversion meant that the best quality TV was only seen at the tracking stations. In recent years, a small team of volunteers in the United States and Australia (including John Sarkissian and Colin Mackellar) came together to search for the recordings made at the stations. Although those tapes were not found, evidence of a backup recording was uncovered. The search for this tape is ongoing. During the search, the best surviving broadcast standard copies of the Moonwalk TV were found and with NASA support, they were restored for posterity and as an enduring tribute to all who made Apollo possible. In addition, the team discovered the high resolution archive copies of EVA TV from the other Apollo missions. Inquiries are being made into the possible restoration of these. The story of how the world saw this remarkable event is a tale of immense technical achievement. This talk will recount the challenge of bringing live TV from the Moon, the search for the original Apollo 11 recordings and the subsequent restoration effort.
Recent observations of the Moon with high resolution imaging spectroscopy have revealed unusual rock types on the lunar farside. These rock types are found near the inner ring of the Moscoviense basin, and are found in three distinct “varieties”, each characterized by high abundances of a single mafic mineral (olivine, low-Ca pyroxene or spinel). The basis of this discovery will be presented, the geology of these peculiar materials will be discussed, and possible formation mechanisms will be discussed. Efforts to evaluate the composition of the olivines found in association with these materials will be explored as well.
The Kepler spacecraft, launched in March 2009, is designed to detect potentially habitable Earths around other stars by detecting the transits of these planets across the disks of their parent stars. This requires performing differential photometry to a precision of 20ppm on a sample of 170,000 stars for a period of 3.5 years. I will present scientific results from the first two years of Kepler data. In addition to several transiting single and multi-planet systems, I will present statistical results on the frequency of planetary candidates around Kepler target stars, and observations of several other interesting (non-planetary) objects.
Meteorites provide an essential source of information on the origin and evolution of the solar system. Chondritic meteorites preserve minerals formed before, during and after the collapse of the solar nebula and proto-planetary disc, while achondrites chart the differentiation and evolution of large planetary bodies such as Mars. Reconstructing the true history of the solar system and its planets relies on accurate interpretation of the minerals present in these samples at the present day – minerals which are far from pristine, rarely primary, and are often not even secondary phases. In this talk I will discuss high and low temperature processes in ordinary chondrites and SNCs, focusing on what the present-day mineral assemblages can reveal about their immediate precursors, earlier generations of minerals, fluids and gases, as well as the processes and events which formed the phases of interest. Techniques discussed will range from two- and three-dimensional petrographic studies through to isotopic analyses of ‘traditional’ carbon and oxygen isotopes and ‘non-traditional’ isotope systems such as iron and silicon. I will also discuss potential avenues of future exploration using the latest generation of instruments for in situ analyses.
Primitive chondrites belonging to petrology type 3 contain silicate stardust grains that formed in the envelopes of evolved stars. I will present the isotopic and elemental compositions of silicate grains that have been identified in four chondrites namely Acfer 094, ALHA77307, SAH 97096, and SAH 97159. The NanoSIMS 50 was used to locate the isotopically distinct silicate grains, followed by PHI 700 Auger Nanoprobe analyses that were done to retrieve elemental information from the same grains. Isotopic and elemental compositions obtained by these two analytical techniques provide complementary information about the identified silicate grains. Oxygen isotopic compositions of stardust silicate grains are orders of magnitude different from those found in solar system materials. For example, the 17O/16O ratio of 1716-4-2 silicate stardust ranges from greater than solar O/O ratio (= 3.8×10) up to ~10. The oxygen isotopic compositions of the silicate grains agree with observations and astrophysical models of red giant (RG) branch and asymptotic giant branch (AGB) stars, and supernovae (SNe). Low-mass RG or AGB stars that have undergone first and second dredge-up episodes show envelope enrichments in 17O and slight depletions in 18O; grains with such oxygen isotopic compositions are the most common in our stardust inventory. Silicate grains with similar 17O enrichments but large 18O depletions may have condensed in low-mass AGB stars that underwent cool bottom processing. Some silicate grains are moderately depleted in 17O and 18O, and have likely originated in low-metallicity, low mass AGB stars. Grains that are enriched in 17O and/or 18O may have condensed in either SN ejecta or high-metallicity stars. Silicon and iron isotopic ratios were measured in rare silicate grains because isotopes of other elements in the same grain help us constrain models of stellar evolution, convective mixing processes, and nucleosynthesis. Differences in the abundances of silicate grains in chondrites belonging to different classes provide clues to the heterogeneities in the grain distributions in the early solar system and secondary alteration processes subsequent to parent body formation. The EH3 chondrite SAH 97159 has a large abundance of silicate stardust, in spite of a history of thermal alteration. Elemental compositions of silicate grains provide pertinent information about stellar grain formation as well as grain survival in the interstellar medium and solar nebula. Silicate stardust predominantly exhibit non-stoichiometric elemental compositions; grains with olivine-and pyroxene-like grains also exist in our inventory. In addition, silicate stardust is Fe-rich with Fe contents reaching up to about 45at.% in contrast to equilibrium condensation models, which predict Mg-rich phases such as forsterite and enstatite to form. Although condensation under non-equilibrium conditions can produce Fe-rich grains, secondary alteration processes may have modified the compositions of some silicate grains in Acfer 094. Finally, composite grains (i.e., grains with multiple subgrains) and grains with SiO2 compositions expected to form only under non-equilibrium conditions have also been identified in situ of ALHA77307.
Humans are demonstrably the largest agent of change today in most of the planet's key functions. This is new development, the impacts of which have yet to be absorbed into national or international policy or planning, or the average person's consciousness. Achieving sustainable societies is a difficult challenge, one made more difficult by mismatches between the natural functioning of our planet and human action and decision making. We will use the example of energy and climate change, which I will argue is training wheels for sustainable societies, to introduce and examine the broader challenges of sustainability.
Studies of meteorites, cometary samples, and interplanetary dust particles have demonstrated that the solar nebula was dynamic--solid grains were transported large distances from where they formed to where they were accreted into their final parent bodies. This transport would have resulted in solids being exposed to a variety of nebular environments in which they were processed, altered, or destroyed, depending on the conditions present and time spent within each environment. I will discuss a new method of studying the dynamics of solid materials over long periods of time. I will also discuss specific applications of this method to understanding the observed properties of meteorites, comets, and IDPs.
In this study we explore the idea that coronae have formed on Venus as a result of gravitational (Rayleigh–Taylor) instability of the lithosphere. The lithosphere is represented by a system of stratified homogeneous viscous layers (low-density crust over high density mantle, over lower density layer beneath the lithosphere). A small harmonic perturbation imposed on the base of the lithosphere is observed to result in gravitational instability under the constraint of assumed axisymmetry. Topography develops with time under the influence of dynamic stress associated with downwelling or upwelling, and spatially variable crustal thickening or thinning. Topography may therefore be elevated or depressed above a mantle downwelling, but the computed gravity anomaly is always negative above a mantle downwelling in a homogeneous asthenosphere. The ratio of peak gravity to topography anomaly depends primarily on the ratio of crust to lithospheric viscosity. Average observed ratios are well resolved for two groups of coronae (∼40 mgal km−1), consistent with models in which the crust is perhaps 5 times stronger than the lithosphere. Group 3a (rim surrounding elevated central region) coronae are inferred to arise from a central upwelling model, whereas Group 8 (depression) coronae are inferred to arise from central downwelling. Observed average coronae radii are consistent with a lithospheric thickness of only 50 km. An upper low-density crustal layer is 10–20 km thick, as inferred from the amplitude of gravity and topography anomalies.
In this study we explore the idea that coronae have formed on Venus as a result of gravitational (Rayleigh–Taylor) instability of the lithosphere. The lithosphere is represented by a system of stratified homogeneous viscous layers (low-density crust over high density mantle, over lower density layer beneath the lithosphere). A small harmonic perturbation imposed on the base of the lithosphere is observed to result in gravitational instability under the constraint of assumed axisymmetry. Topography develops with time under the influence of dynamic stress associated with downwelling or upwelling, and spatially variable crustal thickening or thinning. Topography may therefore be elevated or depressed above a mantle downwelling, but the computed gravity anomaly is always negative above a mantle downwelling in a homogeneous asthenosphere. The ratio of peak gravity to topography anomaly depends primarily on the ratio of crust to lithospheric viscosity. Average observed ratios are well resolved for two groups of coronae (~40 mgal km-1), consistent with models in which the crust is perhaps 5 times stronger than the lithosphere. Group 3a (rim surrounding elevated central region) coronae are inferred to arise from a central upwelling model, whereas Group 8 (depression) coronae are inferred to arise from central downwelling. Observed average coronae radii are consistent with a lithospheric thickness of only 50 km. An upper low-density crustal layer is 10–20 km thick, as inferred from the amplitude of gravity and topography anomalies.
Is Mars still volcanically active today? Have there been geologically recent or present-day volcanic or hydrogeothermal (e.g., geyser) eruptions? Are there “warm havens for life”1? Did magmatism contribute to the formation of martian chaotic terrain and melting of ground ice or release of groundwater to form attendant outflow channels? What has been the role of volcanism in the Valles Marineris, a system of troughs and chasms that span the distance between the chaotic terrain in the east and the Tharsis volcanoes in the west? The sands of Meridiani Planum have been characterized by Opportunity rover investigators as “basaltic”. Where would basalt sand come from? Has there been volcanism in the Meridiani region, a place very far from the major volcanoes of Tharsis, Elysium, Syrtis, and Hesperia? The approach taken to address these questions has been an active one: Select locations for high-resolution imaging and monitor incoming daily global meteorological pictures for evidence of eruptions or new tephra deposits. This effort has involved targeting of the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) narrow angle subsystem and the Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) and HiRISE instruments. It has also involved reviewing daily images from the MOC wide angle subsystem and the MRO Mars Color Imager (MARCI) as well as examination of images and laser altimetry returned by other instruments and spacecraft. The results: No evidence for present-day or very recent (tens of thousands of years) volcanic or hydrogeothermal activity; observation of a lava flow interbedded with sedimentary rock in the Sinus Meridiani region; observations regarding the effect of substrate resistance to erosion on the retention of small (sub-kilometer) impact craters; observation of lava flows and small shield volcanoes in and around the chaotic terrain east of the Valles Marineris; and documentation of landforms across the entire Valles Marineris at 6 meters per pixel, including volcanic features. In addition to these observations regarding Mars volcanism, if the audience is interested, I will briefly discuss the Mars Science Laboratory Mars Hand Lens Imager (MAHLI) investigation and, for the LPI Summer Interns, my career path which began as an LPI intern 25 years ago. (1To borrow a phrase from B. M. Jakosky (1996) New Scientist 150, 38–42)
Tens of thousands of asteroids, ranging in size from meters to kilometers, have orbits that approach or cross the Earth's. An asteroid strike on the Earth could cause local or regional devastation, or even a global mass extinction. Unlike other natural disasters, however, asteroid impacts can be entirely prevented by judicious use of technology that exists today. The orbital properties that make near-Earth asteroids hazardous also make them interesting targets for future human exploration, comparable in difficulty to landing on the Moon. In this talk, I will review the population and character of near-Earth asteroids, survey methods for preventing them from hitting the Earth, and discuss some of the opportunities and challenges they present for human space flight.
Missions to NearEarth Asteroids (NEAs) offer a wide range of possibilities for space exploration, scientific research, and technology demonstration. In particular, manned missions to NEAs represent the perfect environment to gain experience in deep space operations, an indispensable prerequisite for human missions to Mars. Additionally, since human missions are designed as round-trip missions, they provide the ideal platform for sample return. As past robotic missions to asteroids have shown that the environment of an asteroid is highly uncertain before the rendezvous, robotic precursor missions with the objective to characterize NEAs well ahead of the actual human mission are essential. The selection of target asteroids for such precursor missions is directly governed by the target selection for the subsequent human missions. As a starting point for the analysis of human missions to NEAs, an accessibility model for NEAs is developed allowing pre-selection of promising asteroid targets based on the combination of their orbital elements. In the next step, the possibilities of mission abort are examined considering a “free” return scenario and an anytime abort. The “free” return option, characterized by a long return duration and a low ∆v, is found to be feasible for all missions under study. The anytime abort, allowing a comparatively fast return to Earth at a ∆v penalty, is observed to be an option only on short duration missions. Which abort scenarios are possible on a certain mission must be studied on a case-by-case basis. While these abort scenarios apply primarily to human missions, free return and alternative trajectories can assist in the assurance of sample-return mission completion, as motivated by the challenges of the Hayabusa mission. In the scope of the previous investigations,all calculations were based on departures from lowEarth orbit. Current work expands this analysis by assessing Sun-Earth Lagrange (SEL) points as staging locations, potentially reducing onboard fuel and subsequently increasing available payload mass. Both scientific and human missions are considered. In the human scenario, the crew departs directly from low-Earth orbit on their trajectory to the asteroid and rendezvous with cargo, which was previously stationed at a Lagrange point, in the vicinity of the Earth along the outbound trajectory. To achieve this, the feasibility of connecting halo orbits around SEL1 and 2 to the interplanetary trajectories of the spacecraft via invariant manifolds is presently investigated. Biography: Aline Zimmer received a M.Sc. in Aerospace Engineering from the Georgia Institute of Technology. She has been an associate researcher and Ph.D. candidate at the Institute of Space Systems of the University of Stuttgart since 2009 and presently works at NASA’s Jet Propulsion Laboratory.
The Moon is the only solar system body that we have both crater size-frequency distributions (SFDs) and absolute ages of known terrains. These are keystones for understanding the impact rate through time, not only for the Moon but also the Earth, which has had much of its record erased by geologic activity. Previous work constraining the changing lunar impact rate is decades old. New imaging from Lunar Reconnaissance Orbiter Camera (LROC) and results from dynamical calculations of evolution of plausible impactor populations encourage a reevaluation. Therefore, we are compiling the crater SFDs for different lunar terrains (which will later be combined with dynamical research) to understand the evolution of impactor populations and the changing impact rate. Our preliminary data indicates that the SFD of external impactors has likely changed with time, but interpretations of crater SFDs may be considerably affected by unrecognized secondaries.
Images from the Lunar Reconnaissance Orbiter Cameras (LROC), including digital terrain models derived from the LROC Wide- and Narrow-Angle Cameras, and mineralogical data from the Diviner Lunar Radiometer provide evidence that a small volcanic complex featuring silicic eruptive compositions lies at the center of the Compton-Belkovich “thorium anomaly,” known from Lunar Prospector gamma-ray data. The Compton-Belkovich volcanic complex forms a low, broad dome some 25x35 km across and ~1 km in elevation, although the central part of the dome is depressed. Superposed on the broad dome are range of volcanic constructs, from small, circular domes with ~500 m base diameters to intermediate-size, irregular domes up to several km in maximum dimension, to larger volcanic features, up to 6 km base diameter, with summit depressions and flank slopes ranging to over 20 degrees. Within central parts of the broad dome are irregular depressions, interpreted to result from collapse of a near-surface magma chamber following eruptions. Diviner data in the region of the Christiansen Feature show that the broad Compton-Belkovich volcanic complex corresponds to an area of relatively silicic composition. Lunar Prospector gamma-ray thorium data are consistent with Th concentrations as high as those seen in small samples of lunar granite and felsite, known from Apollo samples. We hypothesize that the volcanic complex is the result of a late KREEP-rich intrusion to near the surface where it ponded, likely within megaregolith. Early differentiates erupted along the east and west sides of the structure as the central region collapsed. Late-stage silicic derivative melt compositions then extruded to form domes with a range of morphologies. The Compton-Belkovich volcanic complex is the only silicic, nonmare volcanic feature yet discovered on the Moon’s far side, and it is located ~900 km distant from the Procellarum KREEP Terrane where all of the Moon’s other known silicic volcanics occur.
An ambitious programme of human space exploration will help advance the core aims of planetary science and astrobiology in multiple ways. In particular, a human exploration programme will confer significant benefits in the following areas: (i) the exploitation of the lunar geological record to elucidate conditions on the early Earth; (ii) the detailed study of Near Earth Objects for clues relating to the formation of the Solar System; (iii) the search for evidence of past and/or present life on Mars;(iv) the provision of a heavy-lift launch capacity which will facilitate the exploration of the outer Solar System; and (v) the construction and maintenance of sophisticated space-based astronomical tools for the study of extrasolar planetary systems. In all these areas a human presence in space, and especially on planetary surfaces, will yield net scientific benefits over what can plausibly be achieved by autonomous robotic systems. A number of policy implications follow from these conclusions, which are also briefly considered.
From reflectance spectroscopy, we know that water and hydroxyl exist on the Moon (Pieters et al., 2009; Clark et al., 2009; Sunshine et al. 2009). The origin of the water could be from the formation of the Moon, delivered later by comets, or form continually by proton implantation from the solar wind. Each is a different sort of water, and all could exist. How much, and what kind? That is the question that motivates mapping and monitoring temporal variations of spectral absorption bands near 3 µm as from data acquired by the Moon Mineralogy Mapper (M3) on Chandrayaan-1. However, we need to get around a catch-22: Thermal emission interferes with the shape of reflectance spectra near 3 µm, and the water in the lunar soil absorbs some of the radiation needed to estimate the thermal emission from the spectra. The solution: An independent estimate of the temperature using Lunar Reconnaissance Orbiter's Diviner data. However, thermal emission spectra are complex enough to cause an uncertainty of 40 K from calculations based on thermal infrared data. Subsequently, the topography must be known at high spatial resolution in order to account for multiple reflections from a rough surface. Within a single M3 pixel there are illuminated, hot components and shaded, cold components that result in a broad distribution of temperatures, and multiple reflections that influence the apparent absorption strengths in non-linear ways. Models of planetary surface roughness exist, however, and one of them has been validated in the thermal infrared using Diviner data (Bandfield et al., 2011). We are now using that model to predict the brightness temperature of the Moon as a function of wavelength, lunar local time of day, and albedo. We are looking towards the end of the saga for the characterization of water on the Moon: Are we there, yet?
The Thermal Emission Imaging System (THEMIS) on the 2001 Mars Odyssey Spacecraft has provided thermal infrared (IR) spectra of materials dispersed throughout the low albedo Noachian and Hesperian-aged southern highlands plains units that show a featureless slope towards longer wavelengths. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) visible/near infrared spectral observations for the sites indicate that they are composed of a relatively high albedo anhydrous material, which lacks distinct spectral absorptions. Supported by additional observations such as elevated thermal inertia, location in topographic lows, and distinctive morphology (e.g., light-toned and polygonally fractured), there is compelling evidence for a mineralogical component of chloride salt within the materials. Results of our global survey of THEMIS IR daytime data indicate there are hundreds of local exposures spread throughout the southern highlands plains units. Although these chloride materials may only be representative of relatively short-lived bodies of water, such as the salt pans of Death Valley, the fact that the hydrologic and climatic conditions permitted their formation is important and indicates that many locations throughout the southern highlands must have been substantially warmer and wetter in the past. I will discuss the results of our survey investigating the geologic context of the materials, highlighting the materials’ geologic diversity and prevalence across the southern highlands. Additionally, I will discuss our ongoing efforts to investigate and characterize the proposed chloride-bearing materials and their potential formation mechanisms, including crater age-dating of the materials, detailed stratigraphic investigations, and structural analyses of the polygonal fractures identified within many of the sites. Understanding these materials has implications for the hydrological history of the planet and can provide clues to the evolution of regional and global climate.
Io’s volcanoes dwarf their contemporaries on Earth. Identifying the style of volcanic activity in low spatial resolution data (all we are likely to get for the foreseeable future) allows more advanced modeling of the volcanic processes taking place, leading to a better understanding of how Io’s volcanoes actually work and the individual contribution from each volcano to Io’s heat flow. Paterae, Io’s ubiquitous volcanic feature, are of particular interest as some of them almost certainly contain active lava lakes. These are features which are prime targets for answering the most important question about Io’s volcanic activity, that of dominant magma composition. A persistent lava lake is the top of a column of magma connected to a deep-seated reservoir. As such, they are windows into the interior of the Earth. Although rare on Earth, persistent active lava lakes of immense size are found on Io. Io’s lava lakes, like other manifestations of volcanic activity, are so large because Io is caught in a gravitational tug-of-war that includes Jupiter, Europa and Ganymede. Intense tidal heating leads to the high level of volcanic activity observed there. As tidal heating is most exaggerated at Io, this is the best place to study the process. The best way to constrain interior structure of Io is to measure the eruption temperature of the dominant silicates, which immediately applies constraints on the degree of interior melting and dissipation within Io. One of the best places to make this crucial measurement is at an active lava lake. Lava lakes (in the most extreme environments on Earth, as it happens) have been studied to better understand the processes taking place and to design observations for future missions to Io. Constraining Io’s interior state will help us understand the interior state of neighbouring moon Europa, the likely target of NASA’s next flagship mission to the outer Solar System. Bio: Ashley Gerard Davies is a Research Scientist at the Jet Propulsion Laboratory – California Institute of Technology, in Pasadena, CA, and is an expert in the remote sensing of volcanic activity. He obtained a Ph.D in volcanology from Lancaster University, UK, in 1988. He joined JPL in 1994 as a Post-Doctoral Associate, and as a full-time Scientist in 1996. He was a member of the Galileo Near Infrared Mapping Spectrometer Team, and is Principal Investigator on several studies investigating volcanic activity on Io and Earth. He was a recipient of the 2005 NASA Software of the Year Award for his work on spacecraft autonomy, and is the author of “Volcanism on Io – a Comparison with Earth”, the definitive guide to Io’s volcanoes.
Many studies investigating the petrology of terrestrial and extraterrestrial rocks take advantage in the use of mineral-mineral or mineral-melt element partitioning to retrieve intensive variables and to model magmatic processes, relying on the assumption that chemical equilibration occurs during the solidification of magmas. However, there is now a rising recognition that total equilibrium is not necessarily the rule in natural systems. Cooling kinetics is one of the most important criteria of the solidification process which defines the resulting textural and chemical features of igneous rocks. As the cooling rate is increased, growing crystals and coexisting melts progressively depart from the equilibrium condition in response to reaction kinetics that affect the crystallization path of magmas. In light of this, the compositional variation of the major crystalline phases commonly found in terrestrial and extraterrestrial basaltic rocks and the partitioning of major elements between crystals and melt have been experimentally measured as a function of the cooling rate. Crystals were grown from a basaltic melt at the pressure and buffering conditions of 0.1-500 MPa and NNO+1.5-QFM respectively, under variable cooling rates (0.5, 2.1, 3, 9.4, and 15 °C/min) and isothermal temperatures (1000, 1025, 1050, 1075, 1090, and 1100 °C). Results show that euhedral, faceted crystals form during isothermal and slower cooling experiments exhibiting idiomorphic shapes. In contrast, dendritic crystals are observed from faster cooled charges. As the cooling rate is increased, the compositional variations of the crystals can be summarized as follows: (i) pyroxene is progressively depleted in Ca, Mg, Fe2+ and Si and enriched in Na, Fe3+, Al and Ti; (ii) concentrations of Al, Ca, Fe and Mg in plagioclase increase, whereas Si, Na and K decrease and; (iii) spinel is depleted in Ti and enriched in Al and Mg. The disequilibrium growth of the crystals from rapidly cooled charges implies that chemical elements are rejected less efficiently into the melt next to the crystal surface. This disparity in growth versus diffusion rate develops a boundary layer at the crystal-melt interface enriched in incompatible elements that are incorporated in growing crystals. As a result, element distributions between crystals and melt monotonically depart from their equilibrium values over the effect of cooling rate; importantly, these kinetically-controlled exchange reactions allow the calibration of geospeedometry models principally based on cationic substitutions in the crystal structure. However, in spite of the variation of single-element distribution coefficients, the thermodynamic expression for the Fe-Mg exchange between pyroxene and melt ceases to be a guarantee of equilibrium; in contrast, since Fe and Mg are minor elements in plagioclase, they have the potential to reveal the disequilibrium growth conditions of feldspars with respect to pyroxene crystals in which they are highly compatible. Thermometers, barometers, and hygrometers derived through the crystal–liquid equilibria have been tested at these non-equilibrium experimental conditions. Since such models are based on the assumption of equilibrium, any form of disequilibrium will yield errors. Accordingly, errors on estimates of temperature, pressure, and melt-water content increase systematically with increasing cooling rate, depicting monotonic trends towards drastic overestimates. Errors on estimates are also well-correlated with the variation of element distribution coefficients, consistently with the slow re-equilibration of early-formed crystals during the transition of the silicate melt to a fully solidified magmatic rock.
Although most CR carbonaceous chondrites show little to no signs of thermal metamorphism, CR2 chondrites GRO 03116 and GRA 06100 contain mineral assemblages that formed at significantly high temperatures that secondary minerals in other CR chondrites. Based on SEM, EPMA, FIB-TEM observations, impact-driven hydrothermal origin is discussed.
This seminar will report on my contribution in utilizing and interpreting some of the remotely sensed data acquired through the new and intensive phase of lunar research, which started in the 1990s. The broad conclusion we have drawn from these missions is that the lunar surface, and by implication the underlying geology, appears to be rather more diverse than what we understood from the Apollo-Luna era findings. I will discuss my past and ongoing study of the Imbrium basin region, starting from my work based on VIS-NIR spectral data from the Clementine mission. For my PhD research, I integrated compositional (Fe-Ti wt%) maps with surface images to trace potential mineralogical variations across the lunar surface. I combined this photogeological mapping with crater counting/relative age estimations, all contributing to building a chrono-compositional map of the region. This investigation confirmed the recognised compositional regions within Mare Imbrium and added several others, but also questioned some aspects of the validity of this type of investigative approach, in particular using crater counting as an ‘absolute and precise’ tool of age estimates instead of strictly comparative. Since 2008 I have been working on high-spatial and -spectral resolution data (~220 meters, 6 nm, respectively) in the Near-InfraRed (NIR, 0.9-2.4 µm spectral range) from the SIR-2 instrument on board the Chandrayaan-1 mission to the Moon. NIR spectral reflectance carries the signatures of key mineral components of solid planetary bodies, such as pyroxenes and olivine, thus, in principle, allowing for a geological remote sensing survey of the lunar surface materials containing these minerals. I will illustrate the challenges posed by the lack of reflectance data in the visible range around and below 0.9 micron, thus, making the process of continuum removal problematic (the so called reddening of the spectra). Furthermore, the solar radiation sent back into space is dependent on the nature and physical state of the target surface, which tends to absorb, scatter, and even reflect the incoming energy unevenly across the NIR spectrum. Trying to unscramble the diagnostic absorption features of a given spectrum and attribute them to a specific mix of mineralogical phases represents a mighty and complicated task, without considering the physical attributes of the surface materials, the effects of soil gardening and maturing, changing morphology, shifting viewing angles, and shadowing effects. I will discuss the steps that the SIR-2 team and I took to make sense of the spectral characteristics of the collected solar reflected light and translate them into geologically meaningful results. Specifically, I will illustrate my personal journey to make sense of the available data: my dead-end approaches, the re-discovery of known spectral trends and properties, the application of established mathematical analytical techniques, and finally, the design of a new investigative method made possible by the particular nature of the SIR-2 data set [Comparative Normalisation Analysis (CNA)]. This approach appears to minimise the effects of soil maturity and morphological shadowing allowing for a first-order comparative classification and grouping of spectral types across the lunar surface. I will report on the latest developments of this method, which is presently undergoing a stage of further calibration and testing against published laboratory (RELAB) spectra, plus tantalising preliminary scientific results.
Understanding of fundamental magmatic processes requires quantitative data on the kinetics of crystal growth and dissolution in silicate melts. However, the interpretation of classical crystal growth experiments is often hampered by nucleation delay, melt convection, and diffusion. Recent experiments of thermal melt migration through olivine crystals indicate that they may serve to collect basic physicochemical data on crystal growth at low undercoolings (Schiano et al., 2006). Here, glass inclusions in clinopyroxene phenocrysts were reheated and submitted to a sustained thermal gradient. Each remelted inclusion undergoes a transient textural and chemical reequilibration and concomitantly begins to migrate along a crystallographic direction, at a small angle with the thermal gradient. The completion of morphological evolution requires a characteristic time that is governed by chemical diffusion. Chemical reequilibration results in the formation of a colored halo that delineates the former location and shape of the inclusion after it has migrated away. Transcrystalline migration proceeds by dissolution of the host clinopyroxene ahead and precipitation astern. Its rate is limited by the crystal-melt interface kinetics. Clinopyroxene dissolution and growth are slower than for olivine in similar conditions but obey the same analytical law, which can be transposed to equally or more sluggish melting or crystallization events in nature. When a gas bubble is initially present, it responds to elastic forces by quickly shifting toward the cold end of the inclusion, where it soon becomes engulfed as an isolated fluid inclusion in the reprecipitated crystal. This results confirms that transcrystalline melt migration, beside its possible implications for small-scale melt segregation and fluid-inclusion generation in the Earth’s mantle, provides an experimental access to interfacial kinetic laws in near-equilibrium conditions. Pallasites are differentiated meteorites consisting primarily of olivine and metal. They provide a unique sample from the deep interiors of the solar system parent bodies altogether with critical informations about the differentiation processes that occurred within them. However, there has been controversy regarding there origin and physical positions of pallasites in their parent body(ies). To answer these questions, we studied the olivine-hosted melt inclusions from the Brahin pallasite. In particular, two contrasted sets of melt inclusions were evidenced. The first set consists of plans of secondary inclusions containing abundant chromite and assemblies of metal, sulfide, and phosphoran olivine; the second set corresponds to isolated inclusions consisting for the most part of stanfieldite, a gas bubble, and phosphoran olivine. Melt inclusions in Brahin seem to record a two-stage melting in the Brahin pallasite parent body. Secondary inclusions may have formed during a shock event that created the current stony-iron assembly of the Brahin pallasite. However, stanfieldite inclusions may originate from a pre-pallasitic shock event.
We have measured the oxygen isotopic composition of the solar wind, captured and returned to Earth by NASA's Genesis mission. The data demonstrate that the Earth, Moon, Mars, and bulk meteorites are depleted in 16O by ~7% relative to the bulk solar system in a non-mass-dependent manner. Gas phase photochemistry, occurring either in the solar nebula or in its progenitor molecular cloud, is most likely responsible for changing the isotopic composition of planetary materials in the inner solar system prior to planetesimal accretion. Understanding how, when, and where the rocky planets acquired an isotopic composition distinct from the average composition of the dust and gas from which the solar system formed is a major challenge for the science of planetary origins.
Most of the global warming observations, scientific interest and data analyses have concentrated on the earth Polar Regions and forested areas, as they providedirect measurable impacts of large scale environmental changes. Unfortunately, the hyper-arid environments, which represent ~10% of the earth surface, have remained poorly studied. Yet water rarity and freshness, drastic changes in rainfall, flash floods, high rates of aquifer discharge and an accelerated large-scale desertification process are all alarming signs that suggest a substantial large-scale climatic variation in those areas that can be correlated to theglobal change that is affecting the volatile dynamic in arid zones. Unfortunately the correlations, forcings and feedbacks between the relevant processes (precipitation, surface fresh water, aquifer discharge, sea water rise and desertification) in these zones remain poorly observed, modeled, let alone understood. Currently, local studies are often oriented toward understanding small-scale or regional water resources and neither benefit from nor feedback to the global monitoring of water vapor, precipitation and soil moisture inarid and semi-arid areas. Furthermore techniques to explore deep subsurfacewater on a large scale in desertic environments remain poorly developed making current understanding of earth paleo-environment, water assessment and exploration efforts poorly productive and out-phased with current and future needs to quantitatively understand the evolution of earth water balance. In this talk we will try to address those deficiencies from a comprehensive mapping experiment of shallow subsurface hydro-geological structures in the western Arabic peninsula in Kuwait, using airborne low frequency sounding radars with the main objectives to characterize shallow fossil aquifers in term of depth, sizes and water freshness. We will discuss the implication of these results for subsurface water exploration on Mars and for performing future airborne and orbital detailed mapping of the occurrence and spatial distribution of shallow aquifers in the most arid desert regions on Earth.
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