The Case for a Bajada at Gale Crater, Mars

Based on analysis of CTX, HRSC and THEMIS images, the landing ellipse for Mars Science Laboratory in Gale Crater is situated on the western side of a coalescing fan system, or bajada, that extends in west to east direction for about 60 km. The distal end of the fan system may include lacustrine facies and exhibits in some cases enhanced thermal inertias as compared to surrounding areas. The fluvial distributary system for the fans is evident as a set of degraded channels (some showing inverted relief) that extend southward from the northern rim of Gale Crater, and occasionally the cachements extend beyond this rim to the north. Analysis of CRISM hyperspectral data covering 0.4 to 2.5 μm shows albedo and color variations that correlate with surface morphology for this coalescing system. For example, relatively smooth plains within the landing ellipse are darker and redder than the high thermal inertia portion of the largest fan, located to the north. The two units are separated by an erosional boundary. Detailed mineralogic inferences from analysis of CRISM data are ongoing and will be reported as part of this paper; they are likely associated with varying amounts of ferric oxides and oxyhydroxides.