Raman Analysis of Weathered Rocks from the Fido Mars Rover Test Site, Silver Lake, California

Introduction. FIDO is the prototype rover for the Mars 2003 mission, complete with an Athena-like science payload [1]. FIDO will be deployed in April 1999 for a series of tests at Silver Lake, CA [2]. In preparation for these tests, we have examined a suite of rocks collected at the site to anticipate the problems expected in field analyses on available rock surfaces as opposed to surfaces that have been prepared in the laboratory for optimal analysis conditions. The results presented in this abstract are qualitative. We are also conducting systematic analyses to quantify the Raman spectral characterization of specific minerals and rock types, including igneous, metamorphic, and sedimentary varieties , under field conditions. Silver Lake test site. The focus of the 2003 and 2005 Mars rover missions is to traverse across sites and collect samples from areas that may have been ancient shallow seas or lakes, or perhaps hydrothermal systems. The theme is to acquire data and samples to test the hypothesis that Mars once supported warm, wet conditions and that organic materials and perhaps microorganisms developed in such environments. The Silver Lake area, located north of Baker in the Mojave Desert, CA, is an excellent analog for rover trials because of evidence for lacustrine, fluvial, and groundwater processes [3] that were more extensive during the wet Pleistocene glacial epochs and occasionally during the Holocene (e.g., [4]). The features include a break-out channel that catastrophically drained the lake, beach ridges, soil profiles, alluvial fans, and cali-che deposits. Furthermore, bedrock near the site ranges from metamorphosed rocks such as quartzite and gneiss to meta-andesite, to dolostones and limestones. Cobbles of crystalline rock are included in carbonate-cemented gravels and desert pavement. Samples. The variety and setting of different rocks occurring at the Silver Lake test site are described in [3]. Individual cobbles used in our analyses were collected from surfaces of alluvial fans on the northwestern side of the playa. They typically have three distinct coatings. Tops of the cobbles have a dark-gray, glossy, thin coating of desert varnish. Bottoms, which were sitting in fine-grained aeolian accretion mantles, have a red varnish. Both coatings are inferred to be fixed to rock surfaces by bacterial action [4]. Further, a number of the surfaces are coated by thin caliche deposits. Results. Analysis by laser Raman spectroscopy, especially when employed in a linear traverse – point-counting mode [5] allows mineral identification, quan-tification of mineral …