AN OVERVIEW OF CURIOSITY’S SEARCH FOR ANCIENT HABITABLE ENVIRONMENTS

The Mars Science Laboratory (MSL) Rover Curiosity is exploring ancient sediments in Gale Crater in search for evidence for past habitable environments on Mars. Remote sensing observations of the central ~5 km thick mound (Mt. Sharp) of layered rocks indicate the presence of clay and hydrated sulfate minerals in the mounds basal strata, which suggest aqueous deposition under a variety of conditions, some of which may have favored sedimentary organic matter preservation. These rocks are the mission’s primary science target. Another prominent feature of Gale Crater is the Peace Vallis Alluvial fan that extends from the northern rim of Gale toward the dune field at the base of Mt Sharp. In the distal region of this fan is Yellowknife Bay (YKB), ~500 m east of the Bradbury landing site and one of the lowest points of the current Gale Crater floor. Curiosity’s initial drive to YKB was strongly motivated by an important contact of three major mapping units, including one of high thermal inertia, and the need to understand the units that underlie and/or contact the lower mound units. The full instrument payload and drill onboard Curiosity was used to study a section of fluvio-lacustrine sedimentary rocks (showing some signs of volcanic influence), known as Yellowknife Bay formation, which could be as young as middle Hesperian to even early Amazonian. Collectively, detailed stratigraphic, sedimentological, textural, geochemical and mineralogical data provide support for a habitable subaqueous sedimentary environment that persisted from 100’s yrs to 10’s Kyrs. Sedimentary fabrics reveal active early diagenetic processes and the influence of at least two generations of fluids. Chemical and mineralogical data indicate mudstones of the Sheepbed member were most likely deposited in a low salinity, circum-neutral pH lake. Drilling provided striking images of grey mudstones, previously unfamiliar on Mars, that together with other evidence indicate variable redox states. Curiosity left YKB for the lower mound strata of Mt. Sharp in early July 2013 to explore its intriguing ancient record of environmental evolution as indicated by variations in remote mineralogical signatures.