Timothy D. Glotch

Mineralogy at Meridiani Planum from the Mini-TES experiment on the opportunity rover

The Miniature Thermal Emission Spectrometer (Mini-TES) on Opportunity investigated the mineral abundances and compositions of outcrops, rocks, and soils at Meridiani Planum. Coarse crystalline hematite and olivine-rich basaltic sands were observed as predicted from orbital TES spectroscopy. Outcrops of aqueous origin are composed of 15 to 35% by volume magnesium and calcium sulfates [a high-silica component modeled as a combination of glass, feldspar, and sheet silicates (∼20 to 30%)], and hematite; only minor jarosite is identified in Mini-TES spectra. Mini-TES spectra show only a hematite signature in the millimeter-sized spherules. Basaltic materials have more plagioclase than pyroxene, contain olivine, and are similar in inferred mineral composition to basalt mapped from orbit. Bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites. Bright wind streak material matches global dust. Waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering.

Chloride-Bearing Materials in the Southern Highlands of Mars

Chlorides commonly precipitate during the evaporation of surface water or groundwater and during volcanic outgassing. Spectrally distinct surface deposits consistent with chloride-bearing materials have been identified and mapped using data from the 2001 Mars Odyssey Thermal Emission Imaging System. These deposits are found throughout regions of low albedo in the southern highlands of Mars. Geomorphologic evidence from orbiting imagery reveals these deposits to be light-toned relative to their surroundings and to be polygonally fractured. The deposits are small (< ∼25 km2) but globally widespread, occurring in middle to late Noachian terrains with a few occurrences in early Hesperian terrains. The identification of chlorides in the ancient southern highlands suggests that near-surface water was available and widespread in early Martian history.

Diviner lunar radiometer observations of cold traps in the moon's south polar region

Watering the Moon About a year ago, a spent upper stage of an Atlas rocket was deliberately crashed into a crater at the south pole of the Moon, ejecting a plume of debris, dust, and vapor. The goal of this event, the Lunar Crater Observation and Sensing Satellite (LCROSS) experiment, was to search for water and other volatiles in the soil of one of the coldest places on the Moon: the permanently shadowed region within the Cabeus crater. Using ultraviolet, visible, and near-infrared spectroscopy data from accompanying craft, Colaprete et al. (p. 463; see the news story by Kerr; see the cover) found evidence for the presence of water and other volatiles within the ejecta cloud. Schultz et al. (p. 468) monitored the different stages of the impact and the resulting plume. Gladstone et al. (p. 472), using an ultraviolet spectrograph onboard the Lunar Reconnaissance Orbiter (LRO), detected H2, CO, Ca, Hg, and Mg in the impact plume, and Hayne et al. (p. 477) measured the thermal signature of the impact and discovered that it had heated a 30 to 200 square-meter region from ∼40 kelvin to at least 950 kelvin. Paige et al. (p. 479) mapped cryogenic zones predictive of volatile entrapment, and Mitrofanov et al. (p. 483) used LRO instruments to confirm that surface temperatures in the south polar region persist even in sunlight. In all, about 155 kilograms of water vapor was emitted during the impact; meanwhile, the LRO continues to orbit the Moon, sending back a stream of data to help us understand the evolution of its complex surface structures. A controlled spacecraft impact into a crater in the lunar south pole plunged through the lunar soil, revealing water and other volatiles. Diviner Lunar Radiometer Experiment surface-temperature maps reveal the existence of widespread surface and near-surface cryogenic regions that extend beyond the boundaries of persistent shadow. The Lunar Crater Observation and Sensing Satellite (LCROSS) struck one of the coldest of these regions, where subsurface temperatures are estimated to be 38 kelvin. Large areas of the lunar polar regions are currently cold enough to cold-trap water ice as well as a range of both more volatile and less volatile species. The diverse mixture of water and high-volatility compounds detected in the LCROSS ejecta plume is strong evidence for the impact delivery and cold-trapping of volatiles derived from primitive outer solar system bodies.

Two Years at Meridiani Planum: Results from the Opportunity Rover

The Mars Exploration Rover Opportunity has spent more than 2 years exploring Meridiani Planum, traveling ∼8 kilometers and detecting features that reveal ancient environmental conditions. These include well-developed festoon (trough) cross-lamination formed in flowing liquid water, strata with smaller and more abundant hematite-rich concretions than those seen previously, possible relict “hopper crystals” that might reflect the formation of halite, thick weathering rinds on rock surfaces, resistant fracture fills, and networks of polygonal fractures likely caused by dehydration of sulfate salts. Chemical variations with depth show that the siliciclastic fraction of outcrop rock has undergone substantial chemical alteration from a precursor basaltic composition. Observations from microscopic to orbital scales indicate that ancient Meridiani once had abundant acidic groundwater, arid and oxidizing surface conditions, and occasional liquid flow on the surface.

Soils of Eagle Crater and Meridiani Planum at the Opportunity Rover Landing Site

The soils at the Opportunity site are fine-grained basaltic sands mixed with dust and sulfate-rich outcrop debris. Hematite is concentrated in spherules eroded from the strata. Ongoing saltation exhumes the spherules and their fragments, concentrating them at the surface. Spherules emerge from soils coated, perhaps from subsurface cementation, by salts. Two types of vesicular clasts may represent basaltic sand sources. Eolian ripples, armored by well-sorted hematite-rich grains, pervade Meridiani Planum. The thickness of the soil on the plain is estimated to be about a meter. The flatness and thin cover suggest that the plain may represent the original sedimentary surface.

Highly Silicic Compositions on the Moon

Lunar Reconnaissance The Lunar Reconnaissance Orbiter reached lunar orbit on 23 June 2009. Global data acquired since then now tell us about the impact history of the Moon and the igneous processes that shaped it. Using the Lunar Orbiter Laser Altimeter, Head et al. (p. 1504; see the cover) provide a new catalog of large lunar craters. In the lunar highlands, large-impact craters have obliterated preexisting craters of similar size, implying that crater counts in this region cannot be used effectively to determine the age of the underlying terrain. Crater counts based on the global data set indicate that the nature of the Moons impactor population has changed over time. Greenhagen et al. (p. 1507) and Glotch et al. (p. 1510) analyzed data from the Diviner Lunar Radiometer Experiment, which measures emitted thermal radiation and reflected solar radiation at infrared wavelengths. The silicate mineralogy revealed suggests the existence of more complex igneous processes on the Moon than previously assumed. Remote thermal emission spectroscopy reveals the existence of complex igneous processes on the Moon. Using data from the Diviner Lunar Radiometer Experiment, we show that four regions of the Moon previously described as “red spots” exhibit mid-infrared spectra best explained by quartz, silica-rich glass, or alkali feldspar. These lithologies are consistent with evolved rocks similar to lunar granites in the Apollo samples. The spectral character of these spots is distinct from surrounding mare and highlands material and from regions composed of pure plagioclase feldspar. The variety of landforms associated with the silicic spectral character suggests that both extrusive and intrusive silicic magmatism occurred on the Moon. Basaltic underplating is the preferred mechanism for silicic magma generation, leading to the formation of extrusive landforms. This mechanism or silicate liquid immiscibility could lead to the formation of intrusive bodies.

HiRISE imaging of impact megabreccia and sub-meter aqueous strata in Holden Crater, Mars

High Resolution Imaging Science Experiment (HiRISE) images of Holden crater, Mars, resolve impact megabreccia unconformably overlain by sediments deposited during two Noachian-age phases of aqueous activity. A lighter-toned lower unit exhibiting phyllosilicates was deposited in a long-lived, quiescent distal alluvial or lacustrine setting. An overlying darker-toned and often blocky upper unit drapes the sequence and was emplaced during later high-magnitude flooding as an impounded Uzboi Vallis lake overtopped the crater rim. The stratigraphy provides the first geologic context for phyllosilicate deposition during persistent wet and perhaps habitable conditions on early Mars.

Global Silicate Mineralogy of the Moon from the Diviner Lunar Radiometer

Lunar Reconnaissance The Lunar Reconnaissance Orbiter reached lunar orbit on 23 June 2009. Global data acquired since then now tell us about the impact history of the Moon and the igneous processes that shaped it. Using the Lunar Orbiter Laser Altimeter, Head et al. (p. 1504; see the cover) provide a new catalog of large lunar craters. In the lunar highlands, large-impact craters have obliterated preexisting craters of similar size, implying that crater counts in this region cannot be used effectively to determine the age of the underlying terrain. Crater counts based on the global data set indicate that the nature of the Moons impactor population has changed over time. Greenhagen et al. (p. 1507) and Glotch et al. (p. 1510) analyzed data from the Diviner Lunar Radiometer Experiment, which measures emitted thermal radiation and reflected solar radiation at infrared wavelengths. The silicate mineralogy revealed suggests the existence of more complex igneous processes on the Moon than previously assumed. Remote thermal emission spectroscopy reveals the existence of complex igneous processes on the Moon. We obtained direct global measurements of the lunar surface using multispectral thermal emission mapping with the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment. Most lunar terrains have spectral signatures that are consistent with known lunar anorthosite and basalt compositions. However, the data have also revealed the presence of highly evolved, silica-rich lunar soils in kilometer-scale and larger exposures, expanded the compositional range of the anorthosites that dominate the lunar crust, and shown that pristine lunar mantle is not exposed at the lunar surface at the kilometer scale. Together, these observations provide compelling evidence that the Moon is a complex body that has experienced a diverse set of igneous processes.

Formation of lunar swirls by magnetic field standoff of the solar wind

Lunar swirls are high-albedo markings on the Moon that occur in both mare and highland terrains; their origin remains a point of contention. Here, we use data from the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer to support the hypothesis that the swirls are formed as a result of deflection of the solar wind by local magnetic fields. Thermal infrared data from this instrument display an anomaly in the position of the silicate Christiansen Feature consistent with reduced space weathering. These data also show that swirl regions are not thermophysically anomalous, which strongly constrains their formation mechanism. The results of this study indicate that either solar wind sputtering and implantation are more important than micrometeoroid bombardment in the space-weathering process, or that micrometeoroid bombardment is a necessary but not sufficient process in space weathering, which occurs on airless bodies throughout the solar system.

Spectroscopic characteristics of synthetic olivine: An integrated multi-wavelength and multi-technique approach

Abstract Spectroscopic measurements have been made of two suites of olivine minerals synthesized under slightly different conditions in 5-10 mol% increments across the solid solution from forsterite to fayalite. Here, we present Mössbauer results for the entire Fe-Mg olivine suite, as well as the results for only the fayalite end-member as an introduction to our team’s other diverse spectral-analysis techniques and data that will be presented in forthcoming papers. Experimental methods used to synthesize both suites of samples are discussed here in detail, along with specifics of the analytical techniques used to study them. Electron microprobe data and Mössbauer spectra acquired at 293 K across the solid solution are presented first to characterize and address the presence of impurities in the broad suite of samples that may affect other spectroscopic methods. We then focus specifically on the fayalite end-member to illustrate its properties using multiple techniques. Fayalite is an especially important phase for different types of spectroscopy because, by definition, it contains an equal distribution of Fe2+ cations between the M1 and M2 octahedral sites. Thus, features associated with each of the two sites must represent equal numbers of Fe2+ cations, removing uncertainties associated with assumptions about order/disorder of Fe2+ and other cations. Mössbauer, Raman, thermal emission, attenuated total reflectance (ATR), specular reflectance, and visible to mid-infrared total reflectance studies are presented for fayalite. These include calculation of mid-infrared optical constants (n and k) and fundamental Mössbauer parameters: intrinsic isomer shift (δI), Mössbauer temperature (θM), and recoil-free fraction (f). Data from the different techniques are described and related, demonstrating the importance of multi-wavelength data to provide a complete characterization and understanding of the spectroscopic features in fayalite.