ORBITAL AND 3D CONTEXT OF THE MSL CURIOSITY ROVER'S ALPHA PARTICLE X-RAY SPECTROMETER (APXS) DATA FROM GALE CRATER

The APXS instrument aboard the MSL Curiosity rover measures the bulk chemistry of a rock, soil or regolith target. A map that presents the geochemically classified and individually localized APXS targets, in context of the rover traverse and geology, can shed light on regional trends within Gale crater. Investigation in three dimensions can help place APXS targets into stratigraphic context. This study uses the ~1m/pix HiRISE DTM (Digital Terrain Model) that was produced by the MSL project using HiRISE stereo pairs and the Socet Set photogrammetry software. For this study, the ~0.25m/pix HiRISE mosaic was draped as a basemap onto the DTM, and investigated using ArcGIS and Fledermaus software suites. The geologic map was produced by the MSL project and the main geologic units encountered by the rover are: Bedded Fractured (BT), Rugged (RT), Hummocky Plains (HP), Cratered Surface (CS) and Striated (SR). APXS has encountered all these units so far, except CS unit. The APXS team has classified targets in Gale based on clusters in geochemical variation diagrams. This classification may be integrated with data from other instruments in the future. In ArcGIS, various datasets were integrated to investigate compositional trends (e.g. HiRISE mosaic, rover traverse, geology map, APXS target classification, etc.). The resulting APXS map(s) show the distribution of the APXS-classified targets, revealing compositional trends from Yellowknife Bay to the Kimberley. For example, Yellowknife Bay (in BF) represents typical Mars crust/soil compositions, whereas the Kimberley (in SR) waypoint area represents more potassium- and iron-rich rocks. Three-dimensional space showcases the transitions between classes along the rover traverse, within different geologic units and within stratigraphy. Identification of areas on the map, where we do not have APXS measurements of certain geologic units or rock types, makes one cognizant of future opportunities to fill these gaps. The maps also provide the opportunity to increase our understanding of the local and regional geology of Gale crater and the geochemical transitions between waypoints. The APXS characterization of geologic units identified from orbit provides a guide to trends and changes along the rover traverse, and facilitates comparisons between APXS data from MSL and MER.