Lunar Cold Spots: Granular Flow Features and Extensive Insulating Materials Surrounding Young Craters

Systematic temperature mapping and high resolution images reveal a previously unrecognized class of small, fresh lunar craters. These craters are distinguished by near-crater deposits with evidence for lateral, ground-hugging transport. More distal, highly insulating surfaces surround these craters and do not show evidence of either significant deposition of new material or erosion of the substrate. The near-crater deposits can be explained by a laterally propagating granular flow created by impact in the lunar vacuum environment. Further from the source crater, at distances of ~10-100 crater radii, the upper few to 10s of centimeters of regolith appear to have been “fluffed-up” without the accumulation of significant ejecta material. These properties appear to be common to all impacts, but quickly degrade in the lunar space weathering environment. Cratering in the vacuum environment involves a previously unrecognized set of processes that leave prominent, but ephemeral, features on the lunar surface

Morphology and Composition of the Surface of Mars: Mars Odyssey THEMIS Results

The Thermal Emission Imaging System (THEMIS) on Mars Odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness, implying temporal changes in the processes or environments during or after their formation. Kilometer-scale exposures of bedrock are observed; elsewhere airfall dust completely mantles the surface over thousands of square kilometers. Mars has compositional variations at 100-meter scales, for example, an exposure of olivine-rich basalt in the walls of Ganges Chasma. Thermally distinct ejecta facies occur around some craters with variations associated with crater age. Polar observations have identified temporal patches of water frost in the north polar cap. No thermal signatures associated with endogenic heat sources have been identified

Identification and refinement of martian surface mineralogy using factor analysis and target transformation of near-infrared spectroscopic data

Factor analysis and target transformation techniques were applied to the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral dataset to identify spectral endmembers, reduce noise, and automate image analysis. These techniques allow for rapid processing of images and identification of weak spectral signals. We have applied the automated technique to over 3000 CRISM images and successfully identified endmembers including phyllosilicates (e.g., serpentine, nontronite, and illite), sulfates (e.g., gypsum), carbonates (e.g., magnesite) and hydrated silica. To test these techniques, factor analysis and target transformation were applied to all available full spectral resolution covering the Nili Fossae region from 1.7 to 2. 6 µm data to identify the occurrence of Mg-carbonate in the region. We have also applied the factor analysis and target transformation as a noise reduction algorithm, which also allows for improved results from other common image analysis techniques, including spectral ratios and index maps

A search for minerals associated with serpentinization across Mars using CRISM spectral data

Sites associated with serpentinization processes, both on Earth and throughout the Solar System, are becoming increasingly compelling for the study of habitability and astrobiology. The co-occurrence of serpentine, Mg-carbonate, and talc/saponite on Mars is most like terrestrial sites where this mineral suite is produced in low-temperature serpentinizing environments, and where on Earth these reactions support biological activity. This study aims to understand the global distribution of minerals associated with serpentinization. We performed a comprehensive analysis of the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral dataset using factor analysis and target transformation methods to efficiently parse through the large quantity of data. These methods allow for the rapid analysis of thousands of images and provide a quantitative means to determine the significant spectral constituents of an image. These methods were used to produce a global distribution map of CRISM images with a significant likelihood of containing the spectral types of interest. Previous detections of serpentine using traditional CRISM analysis techniques were typically corroborated and additional detections were identified in isolated locations across the martian southern highlands. Most serpentine across Mars is associated with another Fe/Mg-phyllosilicate phase like talc and/or saponite. Except for in the Nili Fossae region, serpentine shows no clear relationship with ultramafic bedrock or with the other mineral phases investigated (Mg-carbonate and talc/saponite). Most serpentine detections were found in isolated exposures, associated with crater ejecta, knobby terrain, or as part of discontinuous layers in crater or valley walls. Nili Fossae shows more pervasive and extensive detections of a serpentine + phyllosilicate endmember than previously recognized, particularly in the eastern portion of Nili Fossae where the highest concentration of olivine-rich basalts is located. These findings imply that large, regional-scale near surface serpentinizing systems were likely rare on Mars. However, low-concentration serpentine detections across the southern highlands do suggest more pervasive serpentinization early in Mars history, when the planet was more geologically active

Separation of Atmospheric and Surface Spectral Features in Mars Global Surveyor Thermal Emission Spectrometer (TES) Spectra

We present two algorithms for the separation of spectral features caused by atmospheric and surface components in Thermal Emission Spectrometer (TES) data. One algorithm uses radiative transfer and successive least squares fitting to find spectral shapes first for atmospheric dust, then for water-ice aerosols, and then, finally, for surface emissivity. A second independent algorithm uses a combination of factor analysis, target transformation, and deconvolution to simultaneously find dust, water ice, and surface emissivity spectral shapes. Both algorithms have been applied to TES spectra, and both find very similar atmospheric and surface spectral shapes. For TES spectra taken during aerobraking and science phasing periods in nadir-geometry these two algorithms give meaningful and usable surface emissivity spectra that can be used for mineralogical identification

Hydrated silica on Mars: Combined analysis with near-infrared and thermal-infrared spectroscopy

Hydrated silica is found in a variety of martian deposits within aqueously altered mineral suites. Its common occurrence is attributed to its ease of formation in different weathering environments. Because of its presence in disparate units, hydrated silica makes a good tracer mineral to compare otherwise dissimilar martian deposits and relate their relative degrees of aqueous alteration. This work combines near-infrared and thermal-infrared spectroscopy to determine the relative degree of crystallinity and bulk SiO_2 abundance of surfaces containing hydrated silica. A range of crystalline structures are present, from non-crystalline (hydrated glass) to weakly crystalline (opal) to crystalline (quartz), implying a range in the maturity of these silica deposits. However, bulk SiO_2 contents show less diversity, with most martian hydrated silica deposits having SiO_2 abundances similar to Surface Type 2 (basaltic andesite or weathered basaltic composition)—a widespread and common surface composition that suggests limited interaction with water. We also find that hydrated silica crystallinity—as a proxy for degree of alteration—is correlated with the geochemistry of the deposit as inferred by its associated minerals: highly crystalline hydrated silica is found with Fe/Mg-phyllosilicates, moderately crystalline hydrated silica is associated with Al-phyllosilicates, and poorly crystalline phases are associated with sulfates. This corroborates previous predictions of the waning of surficial water from the Noachian → Hesperian and demonstrates the usefulness of hydrated silica as a stand-alone mineral for predicting the degree of alteration of ancient mineral suites

Widespread Shallow Water Ice on Mars at High and Mid Latitudes

The auxiliary information associated with "Widespread Shallow Water Ice on Mars at High and Mid Latitudes" by Piqueux et al. consists of a set of 2 maps (d_m.ascii and TI_SI.ascii) and 2 coordinate files (Lon.ascii and Lat.ascii). - d_m.ascii (720 x 360): Depth to the top of the water ice table, in meter - TI_SI.ascii (720 x 360): Upper (dry) regolith thermal inertia, in J m^2 K-1 s^-1/2 These maps are projected on a simple cylindrical canevas; the coordinates can be using these two files: - Lon.ascii (720 x 1) - Lat.ascii (1 x 360) Resolution is 2ppd. Empty bin are assigned -32768. These files were created from work performed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Government Support Acknowledged

Interpretation of thermal emission. I. The effect of roughness for spatially resolved atmosphereless bodies

International audienceSpacecraft observations of atmosphereless Solar System bodies, combined with thermophysical modeling, provide important information about the thermal inertia and degree of surface roughness of these bodies. The thermophysical models rely on various methods of generating topography, the most common being the concave spherical segment. We here compare the properties of thermal emission for a number of different topographies - concave spherical segments, random Gaussians, fractals and parallel sinusoidal trenches - for various illumination and viewing geometries, degrees of surface roughness and wavelengths. We find that the thermal emission is strongly dependent on roughness type, even when the degrees of roughness are identical, for certain illumination and viewing geometries. The systematic usage of any single topography model may therefore bias determinations of thermal inertia and level of roughness. We outline strategies that may be employed during spacecraft observations to disentangle thermal inertia, level of roughness and type of topography. We also compare the numerically complex and time consuming full-scale thermophysical models with a simplified statistical approach, which is fairly easy to implement and quick to run. We conclude that the simplified statistical approach is similar to thermophysical models for cases tested here, which enables the user to analyze huge amounts of spectral data at a low numerical cost. (C) 2015 Elsevier Inc. All rights reserved