THE CLAY-BEARING UNIT IN GALE CRATER: OVERVIEW AND PLANS FOR INVESTIGATION WITH THE CURIOSITY ROVER

The Mars Science Laboratory (MSL) Curiosity rover will soon be exploring sedimentary strata within the central mound of Gale crater that have distinct mineralogical and morphological properties in orbital data sets, including spectral signatures of Fe/Mg smectite clay minerals (Fox et al. 2017, Cofield et al. 2017). These clay-bearing strata may record significant environmental change within Gale crater (Milliken et al. 2010), and in-situ measurements made by Curiosity will be crucial to understanding the origin of smectite clays and the environmental conditions in which they were deposited. The rover is currently on Vera Rubin Ridge (VRR), a hematite-enriched, erosion-resistant feature on the north-west slope of Mount Sharp (Fraeman et al. 2013), and is expected to descend VRR and arrive at the clay-bearing unit later in 2018. Here we summarize our current knowledge regarding the clay-bearing unit based on the available orbital data sets and discuss the strategic plan for Curiosity’s investigation of this unit.

CRISM spectral signatures consistent with ferric iron smectites were detected within an interval of the Mount Sharp stratigraphy just south of VRR. The strongest CRISM smectite signatures are associated with smooth, linearly ridged terrain. The smooth ridged material appears to be interbedded with a lighter-toned, polygonally fractured material. The stratigraphic relationship between the clay-bearing unit, Vera Rubin Ridge, and strata exposed further up-section remains unclear due to uncertainties in the geometric orientation of these strata.

MSL activities at the clay-bearing unit will address key mission science goals related to 1) the geologic context of Gale crater, 2) the habitability of ancient Mars and the search for modern or relict organic molecules, and 3) the evolution of the martian climate. Several locations within the clay-bearing unit have been identified from orbit as potential targets along Curiosity’s traverse where observations to address these goals will be made: the morphologic subunits of the clay-bearing unit (smooth vs. fractured), the contact between the southern edge of VRR and the clay-bearing unit, a location with very strong smectite signatures (as seen from orbit), light-toned mounds, and the edge of an overlying erosionally resistant unit.