The primary objective of the Thermal Emission Imaging System (THEMIS) experiment, which has been in orbit at Mars since early 2002, is to identify minerals associated with hydrothermal and subaqueous environments. Data from THEMIS have supported the presence of clays, silica‐rich deposits, and chlorides but has not before provided definitive evidence for the presence of sulfates. This is an especially puzzling result given that sulfates have been extensively identified with other instruments at Mars. If present, sufficiently exposed, and in high enough abundances, such minerals should be detectable in orbital thermal infrared spectra at the resolution of THEMIS. The extended mission proposal for THEMIS on Mars Odyssey suggests that the detection of all minerals may be enhanced by observing at an earlier time of day and thus at warmer temperatures. Therefore, in 2009, Odyssey moved to an earlier orbit time. Here, we examine THEMIS data collected when the earlier orbit time coincided with the Martian local (southern) late summer (Ls = 270) for Columbus crater where Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data have detected a number of aqueous minerals. Some of the warmest THEMIS images show evidence for aqueous minerals, although not in the same locations where CRISM finds the highest concentrations. Several factors contribute to this result, including differences in the diurnal temperature curve and levels of induration and particle size. For THEMIS, earlier time‐of‐day and proper seasonal observations combine to provide warm surface temperatures and ideal low atmospheric opacity that significantly increases the ability to definitively identify low spectral contrast aqueous minerals at the surface of Mars.
The discovery of areas of bulk gray hematite on the surface of Mars is among the most interesting of the results from Mars Global Surveyor (MGS). The individual outcrops are concentrated in equatorial, low‐albedo regions from the Valles Marineris to the Meridiani Planum region to the east. While the Thermal Emission Spectrometer (TES) team favored an aqueous process for the formation of this deposit, recent geologic studies have interpreted deposits in the region to have a volcanic origin. Competing ideas for the method of formation of bulk hematite range from aqueous alteration, burial diagenesis, and metamorphism to igneous processes. Here we show that some of the spectra collected over Meridiani Planum and Aram Chaos from the Mariner 6 and 7 spacecraft have a high 3 μm band depth. This feature is associated with hydrated minerals in the surface layer, and the hydrated spectra coincide with the mapped hematite regions. This supports an aqueous mode of hematite formation and, as hematite itself is not hydrated, suggests the presence of other hydrous mineral phases in these areas. We discuss the implications of this association for origin and evolution of these deposits.
The search for evaporites on Mars has important implications for the role that liquid water has played in shaping the planet's geologic, climatic, and potential biologic history. Orbital investigations of surface mineralogy are crucial to this exploration effort. With the exception of coarse‐grained gray hematite at a restricted number of sites and trace amounts of carbonate in globally distributed dust deposits, the Thermal Emission Spectrometer (TES) and Thermal Emission Imaging System (THEMIS) instruments have yet to find widespread mineralogical evidence of aqueously formed minerals. This may reflect the coarse spatial resolution of TES (3 × 5 km/pixel) and low spectral resolution of THEMIS (10 bands between 6.5 and 14.5 μm). Spectral mapping in the Badwater Basin, Death Valley, California, was conducted to better understand the capabilities of TES and THEMIS in detecting evaporite minerals. High‐resolution MODIS/ASTER Airborne Simulator (MASTER) data, degraded to TES and THEMIS spatial resolutions, were used to evaluate the detection limits of sulfates and carbonates. To assess the validity of this spectral remote sensing, a quantitative ground truth analysis of surface mineralogy in the Badwater Basin was performed. The analysis was based on thin section petrography, X‐ray diffraction, electron microprobe, and laboratory and field thermal emission spectrometer analyses. Taken together, the results of all five methods provided enough constraints for a robust interpretation that was in general agreement with the spectral remote‐sensing mapping study for ∼90% of the surface samples examined.
Land surface temperature and emissivity (LST&E) are essential parameters for a wide range of studies undertaken at a variety of spatial scales. LST&E products are generated by a number of spaceborne sensors such as ASTER, MODIS, and AIRS at varying spatial, spectral and temporal resolutions. We have developed an approach for producing gridded, mean, seasonal ASTER LST&E Datasets at a spatial resolution of 100 m at nadir. This paper shows a mean wintertime and summertime emissivity dataset for California and Nevada, USA using all available data since mission launch (2000). Comparison of the two seasonal datasets indicates the greatest variability occurs in areas affected by snow such as the Sierra Nevada Mountains, and in agricultural regions. Comparisons of the new emissivity dataset with laboratory measurements of geologic samples show emissivity differences of less than 0.5%, while 1–3% differences were found for water and vegetation using spectra from the MODIS UCSB library.
