MINERALOGY OF THE GALE CRATER RIM: THE REGIONAL CONTEXT FOR CURIOSITY'S EXPLORATION

In situ exploration by the MSL Curiosity rover at Gale crater will focus on sedimentary clay-, sulfate-, and hematite-bearing sequences in and around Mt. Sharp. Understanding the regional setting of Gale crater, including the composition of the surrounding bedrock, is critical for the successful interpretation of the sedimentary sequences and secondary minerals relevant to questions of past habitability.

Bedrock composition is determined by study of the Gale crater walls with orbital data. Discrete outcrops enriched in olivine and pyroxene, exposed in knobs and small impact craters along the southern and northwestern crater walls, have been discovered using high spatial resolution, near-infrared CRISM data (~20m/pixel). Additionally, spectra of some wall units exhibit 1.9-µm absorptions, indicating the presence of hydrated minerals. Further analyses of CRISM data are ongoing to establish whether these are clay minerals, sulfates, or other hydrated phases.

A key question as the rover traverses units of Mt. Sharp is their provenance. Do sediments comprising the mound represent heavily altered Noachian basaltic bedrock, transported from around the crater and then extensively altered by interaction with fluids? This scenario could explain the apparent absence of mafic minerals. Previous compositional analyses have detected olivine and pyroxene in dunes along the western flank of Mt. Sharp but not in consolidated materials within the mound itself (Rogers & Bandfield, 2009; Milliken et al., 2010; Thomson et al., 2011). Alternatively, do the sedimentary units within Mt. Sharp represent materials derived from further afield, e.g. ash fall from nearby Apollinaris Patera volcano? The greater susceptibility of glassy materials to chemical weathering may require less extensive interaction with water than a basaltic protolith.

Bedrock samples, ballistically emplaced by impact cratering, may lie along the rover’s traverse path, providing a direct means of sampling the composition of altered Noachian crust and the oldest Gale bedrock. In the absence of these data, remote compositional analysis of regional bedrock will be an essential component for discriminating between competing scenarios for the timing, longevity, and environmental setting of aqueous alteration at Gale crater.