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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Launched in 2004, MESSENGER flew by Mercury three times in 2008-2009 en route to becoming the first spacecraft to orbit the innermost planet in March 2011. MESSENGER’s chemical remote sensing measurements of Mercury’s surface indicate that the planet’s bulk silicate fraction differs from those of the other inner planets, with a low-Fe surface composition intermediate between basalts and ultramafic rocks. Moreover, surface materials are richer in the volatile constituents S and K than predicted by most planetary formation models. Global image mosaics and targeted high-resolution images (to resolutions of 10 m/pixel) reveal that Mercury experienced globally extensive volcanism, including large expanses of plains emplaced as flood lavas and widespread examples of pyroclastic deposits likely emplaced during explosive eruptions of volatile-bearing magmas. Bright deposits within impact craters host fresh-appearing, rimless depressions or hollows, often displaying high-reflectance interiors and halos and likely formed through processes involving the geologically recent loss of volatiles. The tectonic history of Mercury, although dominated by near-global contractional deformation as first seen by Mariner 10, is more complex than first appreciated, with numerous examples of extensional deformation that accompanied impact crater and basin modification. Mercury’s magnetic field is dominantly dipolar, but the field is axially symmetric and equatorially asymmetric, a geometry that poses challenges to dynamo models for field generation. The interaction between the solar wind and Mercury’s magnetosphere, among the most dynamic in the solar system, serves both to replenish the exosphere and space weather the planet’s surface.
Evidence for effusive lava eruptions and surface flow has been observed on all terrestrial planetary bodies, but the potential for that flowing lava to erode into the surface to form channels has been widely debated. Analytical models are used to compare the potential for lava to erode three planetary surfaces by two erosion mechanisms, mechanical and thermal erosion. These models are used to simulate the formation of specific features identified as eroded lava channels on the surfaces of Mars, the Moon, and Mercury. Results provide estimates of the effusion rates, lava flow rates, fluid volumes, and erosion rates that are required to form the observed features. These values are used to determine the duration of the associated volcanic eruption as well as to identify potential source and deposition regions, putting the formation of the eroded lava channel into context of the regional geology for each planetary surface considered. Interpretations of model results can be used to constrain 1) whether lava was the most likely fluid responsible for channel formation and what the composition and viscosity of that lava was, 2) when a planet was volcanically active and how quickly lava was erupted onto the surface, and 3) how a planet might be expected to lose heat from the interior during that volcanically active period.
Saturn’s small icy moon, Enceladus, has shown itself to be a surprisingly dynamic place that could act as an oasis for the development of life beyond Earth. Geyser-like plumes, young tectonic features, and relatively warm ice, discovered by the Cassini spacecraft, show that the moon is one of the most active bodies in the solar system. Most of the activity and young geologic features are concentrated in the heavily fractured region known as the south polar terrain (SPT). To explain the higher temperatures and eruptive icy plumes originating from the four largest and most prominent fractures (informally called tiger stripes) in the surface, many models implicitly assume a subsurface global liquid ocean that amplifies the tidal forces produced by the moon’s orbit around Saturn. However, direct evidence for such a body of water is not possible but indirect evidence in the surface features, predominantly fracture orientations, suggests the outer icy shell of Enceladus has rotated nonsynchronously over a global ocean and the solid interior. We show that the fracture patterns in the south-polar region are inconsistent with contemporary stress fields, but instead formed in a temporally varying global stress field related to nonsynchronous rotation (NSR) of a floating ice shell above a global liquid ocean. The fracture sets show a counterclockwise progression in orientation through time, which implies the causal SPT stress field created distinct fracture sets at different points in time. Approximately 153° of counterclockwise rotation relative to the present day surface is preserved in the fracture history of the SPT. Additionally, we have identified potential remnants of ancient tiger stripe-like fractures within the fracture sets that indicate there has been a long history of tiger stripe and plume activity on Enceladus. The present-day tiger stripes are just the latest versions of these tectonic features. Based on our evidence for NSR, new numerical modeling suggests the stresses induced by NSR may be on the order of MPa, much higher than previously modeled diurnal tidal stresses (tens to hundreds of kPa). The larger stresses that result from NSR may be the primary cause of fracturing in the SPT and the ultimate origin of the tiger stripes.
Natural gas hydrate (NGL) occurs both in the earth’s oceans and in permafrost regimes, but in different regions of the (methane) hydrate stability field. NGH occurs in a gas hydrate stability zone (GHSZ), which is stable generally from a cold surface to a subjacent depth determined by increasing temperature. In a GHSZ, the NGH is most stable in the upper part and less stable in the lower part of the zone. The base of the GHSZ is effectively the phase boundary. In addition to understanding in considerable detail the physical chemical drivers of hydrate formation, dissolution, and dissociation, application of the NGH petroleum system holds promise of successful exploration of concentrations of economic scale. And there appears to be very large volumes of gas-in-place in NGH. The key to understanding how NGH may exist and interact with climate and potential biosystems on other bodies in the solar system (and elsewhere) may be best understood by modeling the approximate conditions on these bodies and then using earth analogue examples to further resolve the models. For cold planetary bodies such as Mars, analogues of all three types of permafrost hydrate may be found, and these may be encountered in abundance near enough to the surface to provide a natural resource to support human colonization. On icy bodies such as Europa, a marine analogue of the compound ice cryosphere - NGH stability zone may exist. NGH may be stable in the atmospheres of Jupiter and other gas giants. Because NGH and compound hydrate, which forms from a mixture of hydrate forming gases, acts to sequester natural gas from a gas flux on earth and acts as a climate moderator, it may also have this role in other bodies in the solar system. On Titan, water and the abundant natural gases may generate NGH as part of a materials redistribution system involving water and hydrate-forming gases.
Since its insertion into orbit around Mercury in March 2011, the MESSENGER spacecraft has returned a wealth of information about the volcanic landforms and history of the innermost planet. Extensive surface volcanism was hypothesized after the early Mariner 10 flybys in the 1970s; now, MESSENGER has confirmed a volcanic origin for smooth, vast expanses of plains that differ in color from and embay surrounding terrain, particularly at high northern latitudes. With a global image basemap at 250 m/pixel almost complete, a planet-wide survey of volcanism on Mercury is now possible. This presentation will summarize the current state of knowledge of volcanism on Mercury after almost a year of orbital observations by the MESSENGER spacecraft. In contrast to Earth, the Moon, Mars, and Venus, no large centers of concentrated igneous activity are visible, nor are large shield volcanoes, calderas, or other significant volcanic constructs. The expansive smooth plains observed across the planet, and particularly those northern deposits, may represent the largest scale of surface volcanism. Smaller features, such as sinuous rilles commonly observed on the Moon and Mars, are also largely absent. Those small-scale features that are present include rimless depressions scattered across the planet, which appear to be the sources of pyroclastic deposits. There is also a curious assemblage of channel-like landforms proximal to the northern plains that resemble surface flow features on Earth and Mars, and which may be the product of erosion by high-volume, high-temperature lavas. Finally, the documented contractional history of Mercury, evidenced by abundant thrust faults and related tectonic structures, precludes significant upper-crustal extension and the emplacement of shallow-level igneous intrusions. Accordingly, there are few sites where shallow intrusive activity has unequivocally occurred, suggesting that much of Mercury's surface volcanism is sourced from significant depths.
Geochronological and geophysical data published within the past ten years indicate that plutons are emplaced incrementally over time periods of 10^5 to 10^6 a, and that they do not apparently include more than a few percent melt at geologically significant time scales. This represents an important departure from previously held dogma that pluton-sized liquid magma bodies existed in the upper crust. Although incremental emplacement of magmas is now widely accepted, evaluation of the wide-ranging implications of this hypothesis for pluton-volcano connections and the generation of magma diversity has just begun. One of the most contentious issues in understanding pluton-volcano connections is the origin of huge (>500 km^3) ignimbrite eruptions. Magma emplacement rates calculated from geologic and geochronologic data for plutons (10^-3 – 10^-4 km^3/a) are at least an order of magnitude lower than estimates using comparable data for ignimbrites (10^-2 km^3/a). Thermal models for magma emplacement in the crust predict this rate disparity and suggest that rates of 10^-2 km^3/a or greater are needed to produce large ignimbrite eruptions. However, due to varied exposure, high-precision geochronologic studies of pluton emplacement and ignimbrite eruption for single magmatic centers are scarce. Geochemistry and U-Pb zircon data from the Mt. Princeton batholith and spatially associated ignimbrites in central Colorado indicate that the vast majority of the batholith was assembled incrementally at a rate of 1.5 x 10^-3 km^3/a between periods of ignimbrite eruption. The temporal disconnect between pluton building and ignimbrite eruption events supports the hypothesis that plutons represent magmas that stalled in the crust during periods of low magma flux, and that ignimbrites are generated during periods of high magma flux, without significant residence time or differentiation in the upper crust. Geochronology, geophysics, and thermal models indicate that pluton emplacement must be episodic with individual pulses becoming dominantly or completely crystalline before the next pulse of magma intrudes. This makes it nearly impossible to produce large-scale chemical and textural zoning in plutons by crystal-liquid separation, which challenges many hypotheses. The episodic assembly of plutons also leads to temperature cycling of the magma. Crystal growth experiments in a magma analog (ammonium thiocyanate-cobalt chloride system) at approximately 50ºC, and an alkali basalt at 1150ºC indicate that temperature cycling changes the texture of magmas dramatically. Thermal cycling yields large crystals and decreases crystal number density. In addition, crystal alignment is observed in the magma analog experiments coincident with the thermal gradient during coarsening. Together, these results indicate that temperature cycling of magmas can affect the crystal size distribution and fabric of the resultant rock. Thus, cycling is a variable that needs to be assessed when interpreting igneous textures.
In 1879, George Darwin put forward the idea that the Moon was derived from the rocky portion of the Earth via a process of fission. He speculated that perhaps the Pacific Basin was the scar left from this ancient event. It is easy, with the hindsight gained from the discovery of seafloor spreading and plate tectonics, to look back on this idea as faintly amusing. But in fact, Darwin was doing something remarkable. He was not only speculating about the problem of lunar origin, but was looking at the modern system for evidence that betrays the mechanism of formation. In this talk, I will describe recent developments in the modern theory of lunar origin - the giant impact hypothesis - and recent attempts to forge a connection between the processes accompanying lunar formation via giant impact and the resulting chemical and isotopic signatures observable on the modern Moon.
Surfaces of airless bodies and spacecraft in space are exposed to a variety of charging environments such that a balance of plasma determines the surface’s charge. Photoelectron emission due to intense solar UV radiation is the dominant charging process on the sunlit lunar surface. To first order, this results in a positive surface potential, with a cloud of photoelectrons immediately above the surface, called the photoelectron sheath. Conversely, the unlit side of the body will charge negatively due the collection of the fast-moving solar wind electrons. The interaction of charged dust grains with these positively and negatively charged surfaces, and within the photoelectron and plasma sheaths, may explain the occurrence of dust lofting, levitation and transport above the lunar surface. In order to better understand these surface processes, we have performed laboratory experiments to study the physics of photoelectron sheaths above Zr, glass, CeO2, and JSC-1 surfaces in vacuum. Experimental measurements are compared with the results from a 1D PIC-code simulation to gain a greater understanding of the sheath physics.
Laboratory spectroscopic studies of minerals and ice at micron-scale sizes and wavelengths across the electromagnetic spectrum are vital to understanding the composition and physical nature of dust in many space environments. This talk discusses recent work in laboratory astrophysics on planetary surface dust analogs, e.g., visible and near-infrared (VNIR) wavelength reflectance spectra and optical functions of the species relevant to Mars and Europa as well as interstellar/circumstellar environments. Such data are necessary to maximize the scientific return from VNIR mapping spectrometers aboard orbiting spacecraft by constraining the abundance and distributions of candidate minerals on their surfaces. In particular, hydrated Mg-sulfates, Fe-sulfates, olivine, glasses, etc. will be discussed.
The 40Ar measured in Titan’s lower atmosphere represents approximately 7-9% of the radiogenic argon produced within Titan to date. The overall Ar-degassing efficiency of Titan is thus more akin to that of Mars than that of the Earth. Titan’s moment-of-inertia implies a partially differentiated structure, which can be generally described as possessing a rock+metal core, a middle layer of mixed rock+ice, and a rock-poor upper sequence of, in order of decreasing depth, high-pressure ices, ocean, and ice I and/or clathrate. Assuming hydrostatic equilibrium, Titan is at least 40% differentiated, meaning rock separation from ice, with the principal uncertainty being the mass of the discrete rock+metal core. Such a core may have reaching magmatic temperatures due to radiogenic heating, but at Titan core pressures argon is highly soluble in silicate melts and cannot degas. Whether radiogenic argon produced within cool rock fragments suspended in the slowly convecting, mixed ice-rock middle layer diffuses into the ice matrix depends on whether the rock is altered (hydrated and oxidized) or not. Argon forms a clathrate with water ice to high pressures, however, so 40Ar produced in the mixed ice+rock layer and released to the surrounding ice matrix has likely remained trapped there. The logical source of Titan’s atmospheric 40Ar is the upper sequence of ocean and ice layers, which while nominally rock free may nonetheless have acquired a non-negligible amount of suspended rock fines and dissolved potassium during early melting and differentiation. Over time, such fines and potassium should concentrate in the internal ocean as the bounding ice layers thicken with declining heat flow. At least two pathways appear viable for 40Ar release to the atmosphere from Titan’s ocean: cryovolcanism, and impact disruption of a thin, clathrate-dominated crust. A third alternative posits that Titan accreted undifferentiated, and that its differentiation was a product of the Late Heavy Bombardment. Melting and differentiation of >40% of Titan at 3.9 GYA could have released more than enough extant 40Ar to account for Titan’s present atmospheric inventory.
The NASA Solar Radiation and Climate Experiment, launched in January of 2003, is a suite of instruments that measure the variability of both the Sun’s total solar irradiance (TSI) and its solar spectral irradiance (SSI) over the 110-2400 nm spectral range thereby accounting for more the 97% of the sun’s radiant output. The SORCE spectrometers are able to decompose the TSI signal into its spectral components, and the secular trends in the 300-2400 nm have been measured for the first time. The SORCE instruments have revealed a number of important findings that have significance to the earth-climate system. 1) The Total Irradiance Monitor (TIM) measures the TSI with a precision of ~1.0 part per million (ppm) and very small degradation that is correctable to about 10 ppm. Furthermore, recent laboratory studies have confirmed the absolute calibration of the instrument supporting its reported Solar Cycle 23 solar minimum irradiance value of 1360.75 Wm2, an important finding for Earth radiation budget analyses. 2) The time series from the Spectral Irradiance Monitor (SIM) shows that the observed TSI trend is the sum of offsetting spectral irradiance trends rather than the quasi-uniform change predicted from solar proxy models. The different layers of the Earth atmosphere respond to changes in the SSI so these observations are critical to the understanding of the mechanisms by which solar activity affects the earth climate system. 3) The Solar Stellar Irradiance Comparison Experiment (SOLSTICE) is an ultraviolet (112-310 nm) spectrometer that uses bright, stable ultraviolet stars as a calibration standard. The combined UARS and SORCE SOLSTICE instruments provides a continuous observational record extending back to 1992 covering two solar minimum time periods. As an additional science activity, SOLSTICE also measured the lunar reflectivity in MUV (112-180) nm portion of the spectrum.
Recent near infrared observations from SELENE and M³ have uniquely identified Fe-bearing crystalline plagioclase regions on the Moon. These results are significant because they validate earlier near infrared observations as well as characterize the widespread distribution of crystalline plagioclase across the lunar surface. Regions of nearly pure crystalline plagioclase (<5% olivine and pyroxene) as identified in the near infrared are ideal areas to investigate the utility of thermal infrared Diviner data to constrain plagioclase compositions (AN#). New lab measurements of varying compositions of the plagioclase solid solution series measured under a simulated lunar environment demonstrate that the position of the Christiansen Feature, an emissivity maximum near 8 m, is diagnostic of composition. Thus an integrated near- and thermal-infrared approach will enable plagioclase compositions to be mapped across the lunar surface and is significant for identifying rock types (ferroan anorthosites versus Alkali-suite rocks) and may ultimately constrain their method of formation (magma ocean crystallization or plutons).
Mercury has a rich tectonic history, evident from data returned by the MESSENGER spacecraft that reveal prominent global and regional fault populations as well as broad, long-wavelength lithospheric folds. Global fault populations are comprised of large thrust faults (termed lobate scarps in the planetary literature) that accommodate different styles of shortening deformation, such as distributed faulting of large crustal blocks or concentrated shortening confined to narrow zones. Regional fault populations consist of so-called wrinkle ridges, landforms inferred to be the surface expression of blind thrust faults within smooth volcanic plains. Additionally, smooth plains deposits within large impact craters or basins host populations of normal faults that form a variety of geometric arrays, with a generally continuous succession of complexity from smaller to larger basins. Long-wavelength lithospheric folds, apparent from tilted crater floors, are found throughout all parts of the planet for which topographic data is available, but they are most prominent across smooth plains units. Detailed mapping, geometric analysis of faults and folds, and quantification of strain accommodated by all these structures bring improved insights into processes and mechanisms responsible for their formation. Geometric properties of normal faults in smooth plains within large basins allow estimates of plains thickness, showing that lithospheric folding was an ongoing and long-lived process, starting before, but continuing after, volcanic plains emplacement, leading to significant thickness variations of the volcanic cover on Mercury. However, these large-scale folding did not substantially contribute to global radial shortening. In contrast, new mapping results show that there are far more individual thrust faults than previously counted. This dramatically increases the estimate for planetary contraction to ~5 km, a value that is in agreement with geophysical models for the contraction of Mercury.
It is now clear that hydration on the Moon of both internal and external originhas been discovered. One can easily hypothesize a diversity of sources: comets/asteroids, the solar wind, the lunar interior, and even the interstellar medium. How can we further characterize and discriminate between volatiles from these sources? Can we characterize how have they changed over time? We describe several approaches to accomplishing this.
High-resolution images of Mercury's surface returned by MESSENGER reveal a class of unusual depressions, mostly associated with impact craters. Named hollows, these depressions are shallow with rounded outlines and flat floors. Many hollows have high-reflectance halos and interiors. The hollows have no analog on the Moon but do resemble the "Swiss cheese" terrain found in the polar regions of Mars, thought to form by sublimation of carbon dioxide ice. The morphology of the hollows suggests that they form through loss of a volatile phase when rocks are exposed to the harsh thermal and space-weathering environment of the mercurian surface. Compositional information collected by MESSENGER's elemental sensors over large areas of the planet indicates a higher-than-expected content of sulfur, thus sulfur-bearing minerals may be involved in the formation of the hollows. I will present an overview of these fascinating features and discuss how they fit with other evidence for relatively high volatile content in Mercury.
The impact cratering process has been investigated for nearly 70 years and yet the details of central uplift formation in complex impact craters remain largely uncertain and debated. This field-based study provides insight into central uplift formation in crystalline target rocks based on evidence from the centrally uplifted rocks of the 90 km, 214 Ma-old Manicouagan impact structure (Canada). Numerous methods and techniques have been used to investigate the anorthositic host rocks and various impactites to construct a viable model of uplift emplacement. This study comprises important ground-truth data that can be used to constrain numerical simulations of central uplift formation in crystalline target rocks and provides potential analogies with such craters observed elsewhere (e.g., on Earth or other planetary bodies).
The Mawrth Vallis region has been recognized as having the most expansive exposures of Noachian-aged phyllosilicate bearing layered rocks on the surface of Mars. The Mawrth Vallis stratigraphy consists of a lower Mg/Fe smectite bearing unit and an upper unit containing an assortment of Al phyllosilicate minerals. Recently scattered occurrences of acid sulfate minerals such as jarosite and possibly alunite have been recognized in the region. These identifications have been made on the basis of reflectance spectra measured by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on-board the Mars Reconnaissance Orbiter (MRO). The detection of occurrences of these minerals and their relevance for the early history of aqueous activity on Mars will be discussed.
The mineral zircon (nominally ZrSiO4) is a particularly robust geochronometer and arguably one of the most important minerals available to study the geochemical and geodynamic evolution of the Earth’s crust. The incompatibility of Zr+4 in nearly all major rock forming minerals makes zircon a ubiquitous mineral phase in most geochemical environments, and the low solubility of zircon in crustal fluids (silicate melts and aqueous fluids) makes zircon a largely chemically inert mineral. During residence in the crust, the strong chemical bonds in zircon yield extremely low rates of chemical diffusion, effectively preventing disturbance to the U-Pb geochronological system, even during ultrahigh temperature metamorphism (T = 900–1100°C). Despite a high preservation potential in Earth’s crust, zircon grains extracted from high-grade metamorphic rocks (~1-4 GPa and ~500-1000°C) associated with mountain building, display evidence of alteration, recrystallization, or new-growth. U-Pb dates recorded in these zircon grains are routinely interpreted to represent the timing of peak metamorphic conditions, with geochemical and textural evidence suggesting hydrous metamorphic fluids to be fundamentally important catalysts facilitating zircon reaction and U-Pb date resetting. Because high and ultra-high grade metamorphic rocks are witnesses to the most extreme tectonic and metamorphic processes, linking the geochemistry and geochronology of zircon grains to their metamorphic environment remains one of the most vital yet unresolved barriers to understanding crustal geodynamics. During my talk, I will focus on the use of zircon for unraveling the evolution of mountain belts, and discuss my research on the behavior of zircon during mountain building using geological samples collected from the uplifted and exposed roots of the Dabie Mountains in Central East China, and present the results of an ongoing experimental study to measure element partitioning into zircon using quartz-saturated hydrothermal fluids.
Syrtis Major is a large shield volcano of Hesperian age located in the northern Hemisphere of Mars. I use three methods—spectral index mapping, spectral mixture analysis, and factor analysis and target transformation—to analyze Thermal Emission Spectrometer (TES) data covering this region. These data show that carbonate decomposition products, including lime (CaO), periclase (MgO), portlandite (Ca(OH)2), and brucite (Mg(OH)2), are likely present at the surface of Syrtis Major. Subsurface carbonates have been found in the vicinity of this region, exposed by erosion and crater central uplifts. I suggest that the unique spectral features seen at Syrtis Major are the result of the subsurface interaction of Syrtis magmas with a regional carbonate layer. Devolatilization of subsurface carbonates as a result of this magma-carbonate interaction would have resulted in a pulse of CO2 into the Martian atmosphere during the Hesperian, perhaps providing a brief period of climate warming. Magma-carbonate interaction may also be responsible for the high Ca-bearing pyroxene abundances in the Syrtis lavas and the unique topography and wrinkle ridge patterns seen at Syrtis Major.
This talk will describe recent evidence from orbital data on the origin of strong lunar magnetic anomalies and the history of the Moon's core dynamo. Previous work has shown that central magnetic anomalies in Nectarian-aged basins probably require a core dynamo during that epoch. However, strong anomalies in the highlands indicate a role of basin-forming impacts in producing both magnetic anomaly sources and transient magnetizing fields. Recent work extends the investigation of central anomalies to younger basins and adds further evidence that the strongest anomalies are concentrated antipodal to the youngest lunar basins. In particular, a new concentration of anomalies that is approximately antipodal to the Schrodinger basin is reported.
Though the Moon acts primarily as a passive absorbing obstacle to ambient plasma, its presence can affect the lunar environment to surprisingly large distances. With the new ARTEMIS mission, we can study these effects with unprecedented detail, utilizing its comprehensive plasma instrumentation and two-point measurement capability. We observe a variety of signatures of the Moon-plasma interaction, including protons reflected from lunar remanent magnetic fields, pickup ions from the lunar surface and exosphere, accelerated photo-electrons from the charged lunar surface, and a variety of wave turbulence extending outward from the Moon. These signatures, which result from processes taking place at or near the lunar surface, extend to distances of tens of thousands of km from the Moon, effectively increasing the Moon’s sphere of influence by orders of magnitude. In turn, each of these processes and associated charged particle populations allows us to connect plasma observations back to the Moon’s surface and exosphere, potentially informing us about processes as diverse as surface weathering, volatile implantation, electrostatic charging of the surface, and source and loss processes of the tenuous lunar exosphere.
The asteroids are generally thought of as rocky or metallic bodies, with comets as their ice-rich distant relatives. Metoritical and spectroscopic evidence for OH-bearing minerals on asteroids dates back decades, however, and 2010 saw the first detection of ice (along with organic material) on an asteroidal surface. I will focus on our current understanding of the diversity of OH- and H2O-bearing asteroidal materials, and touch upon the dynamical and physical processes that have created and maintained that diversity over billions of years.
Mercury has been referred to as odd, enigmatic and quirky. Recent discoveries have served to enhance Mercury’s reputation as a bizarre planet. Mercury’s unique space environment, mass, and composition lead to extreme conditions that can serve as important tests for models of geologic processes. The MESSENGER spacecraft recently completed one year in orbit around Mercury. In this presentation I will review major recent discoveries that challenge conventional geochemical and geophysical wisdom and offer some alternative interpretations of Mercury’s surface composition, space weathering products, and volatile inventory.
The first three years of Lunar Reconnaissance Orbiter Camera operations have led to advances in our understanding of lunar geology. To date, a focus of ongoing LROC Science Team investigations has been lunar geomorphology, including analyses Narrow Angle Camera images, digital terrain models derived from geometric stereo observations, and multispectral investigations of key regions. LROC digital terrain models derived from geometric stereo observations can be used to analyze the characteristics of volcanic features, including slope and volume estimates, definition of flow features, determination of depression morphologies, and boulder populations. As an example, the LROC Science Team has characterized the morphometric properties and roughness of more than 150 domes and ~90 cones in the Marius Hills region showing that the Marius Hills volcanic constructs are not silicic. The flow lengths and slopes indicate that the unique morphology of the Marius domes are instead primarily controlled by effusion dynamics. LROC observations and science results are adding to our understanding of lunar geology while defining key targets for future robotic and human exploration.
Near-infrared spectroscopy is a powerful tool for characterizing the mineralogy of iron-bearing minerals in the solar system. When iron is present in pyroxenes, spectra can be used to evaluate major element composition, structure, thermal history, and sometimes even minor element composition. However, without iron, the puzzle becomes more complicated. Together, we will take a tour through the inner solar system, exploring recent NIR spectroscopy-enabled discoveries from our familiar and beloved Moon through the enigmatic Mercury.
Visible and thermal infrared spacecraft datasets are used to gain insight into the nature of the surface materials and upper martian crust, revealing a distinct transition in the physical properties of martian crustal materials that occurred during the Hesperian era. Contrary to a prevailing view of the martian crust as primarily composed of lava flows, we find that most older regions of Mars have morphological and thermophysical properties consistent with poorly consolidated fine-particulate materials that may have a volcaniclastic origin. By contrast, younger surfaces contain blocky materials and thermophysical properties consistent with effusive lava flows. Explosive volcanism is likely to have been dominant on early Mars and these findings have implications for the evolution of the volatile content of the crust and mantle and subsequent development of the surface morphology. This dual nature of the crust appears to be a defining characteristic of martian history.
"Floating near the light Wrapped in its invisible cloak Mercury stands guard"
The ion-drive spacecraft Dawn, part of NASA’s Discovery Program, spent approximately one year in orbit around the asteroid 4 Vesta. A review of the Dawn mission at Vesta and the highlights of the scientific discoveries will be presented.
The origin of the shape of the Moon has been an open problem for 200 years. Recently, we proposed that the shape of the lunar farside is consistent with a crust that grew under the influence of tidal heating during the magma ocean epoch. However, we left open the problem of the shape of the nearside, which should have experienced similar heating effects. Now, we show that when the Moon's topography is analyzed without the South Pole-Aitken basin, its global degree-2 shape is consistent with crustal thickness variations produced by tidal heating. This result links the near and far sides to a common crust building process that predates much of lunar geology.
Basaltic volcanism is the most common type of volcanism on Earth from large shield volcanoes to small scoria cones. The principal mechanism in any basaltic system is the transfer of primitive magma from a deep source to the surface via dikes. Dikes are considered to inject into mode I fractures, opening perpendicularly to the least principal compressive stress (σ3). However, recent studies show that crustal heterogeneities can complicate such a simple propagation pattern. Using a combination of spatial distribution analyses of volcanic centers within monogenetic volcanic fields and analogue modelling of dike propagation within a fractured elastic medium, I tested the role of the stress field and pre-existing crustal fractures acting on dike propagation and thus on the development and evolution of monogenetic volcanic fields. In the case of large shield volcanoes, these are affected by magmatic intrusions, gravitational spreading. Using two natural examples, I tested the impact of dike intrusions on the stability of the flank of shield volcanoes subjected to gravitational spreading using analogue models. In terms of the impact of magmatic intrusions on the upper lithosphere my work shows: 1) the influence of the medium on the propagation of dikes; and 2) the influence of dikes on tectonic structures affecting large volcanic edifices.
Low-sulfide mineralization represents a previously unidentified source of platinum-group elements in the Sudbury area. Until recently exploration around the Sudbury Igneous Complex has focused on two massive base-metal sulfide styles of mineralization: 1) the pyrrhotite dominated Ni-Cu-IPGE contact-type and 2) the chalcopyrite dominated Cu-Ni-PPGE sharp-walled vein type. In contrast to these styles, low-sulfide mineralization displays low modal abundances of sulfide across mineralized intersections, with the primary economic focus being the recovery of precious-metals. This study focuses on five low-sulfide prospects. Extensive core logging and petrographic analysis of samples was undertaken, along with SEM-EDS and EMP analysis of sulfides, precious metal minerals and silicates, the latter of which was used to calculate geothermobarometric equilibrium conditions. LA ICP-MS analysis of sulfides was also undertaken on selected samples, which were combined with whole rock analyses to produce a siderophile and chalcophile element mass balance. This data was combined with whole rock halogen and fluid inclusion analyses to produce a model for the genesis of low-sulfide mineralization and its place within the larger Sudbury mineralizing system. The study of the Sudbury impact structure and its mineralization offers a one-off opportunity to observe the process of impact cratering as a metal concentrating process.
We present a summary of the geophysical data acquired over the Chicxulub impact structure. These data show that the Chicxulub impact structure includes ring faults up to 125 km radially with the crater rim the inner edge of these faults except in the northeast. Slump blocks offset by large faults underlie a terrace zone. The inner blocks underlie the peak ring that exhibits variable relief due to target asymmetries and bounds the intact melt sheet within the central basin. Impact breccias lie within the annular trough above the slump blocks and within the central basin above the melt sheet. Beneath the melt sheet is the top of the central uplift, displaced by >10 km vertically, and an upwarped Moho, displaced by 1-2 km. These results support the following series of events resulting from the 65.5 Ma Impact: within seconds of the impact, a 100 km wide transient cavity formed. Within minutes, fluidized, rebounding crust and mantle rose above the surface, the crater rim underwent brittle deformation and collapsed into large slump blocks resulting in the final crater rim expanding outwards by kilometers, while ring faults formed farther outwards. The fluidized rebounding crust in the center of the impact structure collapsed outwards forming the peak ring, and buried the inner slump blocks. The central rebounded crust submerged to ~5 km and a < 3 km thick melt sheet formed and lapped up onto the peak ring in places reaching the annual trough. Within tens of minutes, slope collapse and ground surge started infilling the annular trough and to a lesser extent the central basin. Within hours to days, tsunami waves brought in large thicknesses of sediments to infill the trough and basin. These images and models at Chicxulub differentiate between existing proposed models and provide opportunity for improving our understanding of impact processes. Future opportunities include: 1) an upcoming drilling expedition to directly sample and log the peak ring and annular trough of the impact structure, and 2) using the subsurface perspective at Chicxulub and other well-preserved Earth impacts to increase our ability to interpret remotely sensed data over non-terrestrial impact structures.
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