OVERVIEW OF 3 YEARS OF CHEMCAM CHEMICAL COMPOSITIONS ALONG THE CURIOSITY’S TRAVERSE AT GALE CRATER, MARS

Curiosity rover has been on Gale crater for ~ 3 years now. It has driven for >10 km from its landing site up to the base of Mount Sharp. The ChemCam instrument, using the LIBS technique, has been widely used in order to assess the chemistry of rocks & soils remotely, as well as to produce images up to the horizon. ChemCam has sampled >1000 targets, corresponding to more than 250000 laser shots and more than 5000 context images. A major LIBS recalibration using > 350 standards was recently completed in order to improve our accuracy. In this study we will highlight the characteristic of each important unit that the rover went through, using this new calibration for ChemCam.

The Bradbury landing site (sols 0-53; 326-520), a plain located at a distal portion of the alluvial fan from Peace Vallis, exposed several float rocks as well as some conglomerates. These rocks have igneous compositions ranging from mafic up to trachytic end-member. These observations provided an important clue concerning the diversity of early Mars magmatism that was not previously recognized.

Another area, called Sheepbed (sols 126-300), is essentially composed of mudstones. Curiosity performed its first drill sampling at this location. The mudstones show a very homogeneous composition, close to the average Martian crust.

The nearby Shaler fluvial sandstone outcrop (sols 306-325), the first outcrop of potential deltaic foreset beds, shows K enrichment. This enrichment is also observed at the Kimberley formation (another drill site flanked by foreset beds), located at 7 km SW of Shaler, with up to 5.3 wt % at the Mount Remarkable member.

The Pahrump outcrop (sols 801-919) corresponds to the first observed material at Mt Sharp’s base, and present a diverse composition, suggesting a stronger alteration.

Further along the traverse, light-toned Murray unit (sols 992 on) contained an outcrop highly enriched in SiO₂ (75-85 wt %) and TiO₂, where a drill has just been performed.

ChemCam also analyzed more than 200 soil locations. The analyses indicated that fine soil compositions are similar to elsewhere on Mars, with some hydration.

Overall, ChemCam has observed a wide variety of rocks, from sedimentary to igneous, with a large diversity of chemistry and implied formation processes.