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Project Progress

During Year 5 of NAI membership, we completed our remote sensing analog studies of the Badwater Basin in Death Valley designed to evaluate spatial resolution detectability thresholds for a variety of evaporite minerals under natural geological conditions (e.g. complex mixtures involving silicates) and at the spatial resolutions of the Thermal Emission Spectrometer (TES) and Thermal Emission Imaging System (THEMIS) instruments, both of which are presently mapping from Mars orbit. The work had two basic thrusts: Predictive mapping of surface mineralogy using high altitude remote sensing (MASTER) data and the Environment for Visualizing Images (ENVI) analysis tools, as well as ground truth, involving field spectroscopy and lab determinations of mineralogy. This work was submitted to the Journal of Geophysical Research-Planets and is presently in review. The basic findings follow: At TES resolution (3 km/pixel), carbonate abundances were at the detection limit in Death Valley, while sulfates were not detectable. However, at THEMIS spatial resolution (100 m/pixel), both carbonates and sulfates were detectable. The flat responses of halite in the mid-infrared (IR) rendered it essentially invisible at both resolutions. The next phase of this research will examine the spectral resolution thresholds for the same data sets. This work formed the basis for a Masters Thesis by Alice Baldridge, who defended last year and is presently in the PhD program at ASU.

A second study completed during Year 5 was a study of the margins of the Martian North polar remnant ice cap to search for sites of possible magma-cryosphere (volcano-ice) interactions. The study commenced with broad photogeological reconnaissance using Viking data to identify potential water-formed geomorphic features. This was followed by detailed studies at four sites, selected to cover a range of potential processes. Hypotheses posed for the origin of geomorphic features were tested using Mars Orbiter Laser Altimeter (MOLA) data and geographic-information-system (GIS) tools (e.g. Digital Elevation Models) and comparisons to terrestrial analogs. In the course of this work, we discovered that MOLA data are sensitive to subglacial topography in areas that have been recently deglaciated, but are now covered by snow. This ability to see through the ice has opened up our access to polar geological history using MOLA topography. In addition, the hypothesis of a pseudocrater origin for a small field cinder cone-like features was tested using MOLA data. It was determined that they are more likely of a subglacial origin, but still formed by a process involving liquid water. At another site, we discovered that small coniform features hypothesized to be of volcanic origin are likely of a volcanic origin and that associated channels may have been formed by hydrothermal outflows. Finally, we investigated the margins of Chasma Boreal, a major re-entrant feature in the North polar cap margin and two associated chasmata. We documented additional evidence to support a formation by subglacial outfloods along the ice margin very recently in Martian history. The first three of the study sites have been written up and submitted to the Journal of Geophysical Research-Planets and Icarus. Our study of the Chasma Boreal site is still in progress and awaiting new data releases from THEMIS expected in the Fall. The above studies formed the basis for a Masters thesis by Meredith Payne, who successfully defended in December 2002 and is now enrolled in a PhD program at ASU.

A highlight of Year 5 was the publication in Science of a paper by Co-I Christensen that provided an alternative hypothesis for the origin of the numerous seep sites identified previously by Mailn and Edgett with Mars Orbiter Camera (MOC) data. Christensen’s paper, based on THEMIS visible imaging, suggests that the seeps could have formed beneath snow-pack that accumulated during a recent period of low obliquity, and not by outflows of subsurface water (e.g. hydrothermal brines) as previously suggested.

Reconnaissance studies of Astrobiology landing sites on Mars for the Mars Exploration Rover mission (successfully launched in June), and detailed studies of the Gusev Crater site constituted another major focus of the project during Year 5. Gusev was selected as the site for the first MER landing, scheduled to occur in January 2004. Detailed studies of the second landing site for MER, the hematite site at Meridiani Planum, were also carried out incorporating new imaging data from the Odyssey Mission. Results of these Mars landing site studies were presented at a community landing site workshop, to the Mars Exploration Assessment Group (MEPAG), and to the MER project team.

In addition to planning for NASA missions, Ronald Greeley also participated extensively in planning for the Mars Express mission, which was successfully launched by the European Space Agency in 2003. Greeley is a Co-Investigator on the German High Resolution Stereo Camera, and he provided our list of high priority imaging targets for Astrobiology to the High Resolution Stereo Camera] (HRSC) imaging team.