FIRST FIELD RECONNAISSANCE GEOLOGIC MAPPING ON MARS USING THE MARS EXPLORATION ROVER SPIRIT

Chemical, mineralogical, and lithologic variations within generalized terrain units previously mapped in orbital Mars Reconnaissance Orbiter/High Resolution Science Imaging Experiment image data are documented for the first time on the surface of Mars through in situ observations during the Mars Exploration Rover mission. Direct field observations on Mars made from the rover perspective during Spirit’s traverse through the Columbia Hills, Gusev Crater, Mars (sols 156 to present) now support the conclusion that (1) Mars is geologically complex at meter length scales, (2) the record of its geologic history is well preserved and exposed, (3) stratigraphic units may be identified and correlated across significant areas on the ground, and (4) outcrops and geologic relationships between materials may be analyzed with techniques commonly used in the field on Earth. The last point validates a fundamental, and until now experimental, design criteria for the MER mission.

Based on this field study we can say that the Columbia Hills have recorded several events not obvious from orbital observations alone. We can also demonstrate from direct observation (characterized rocks above and below a major unconformity) that the early history of Mars was a time of widespread deposition and modification of what are now stratigraphically correlatable materials. Fluids in degrees that varied laterally within the same map unit have substantially altered volcanoclastic and impactite protoliths geochemically and mineralogically. Summary stratigraphic results show that subsequent geological activity and atmospheric interaction with the surface, although much reduced in rate and scale of fluid involvement, has occurred over geologic time sufficient enough to result in widespread alteration products and significant landscape erosion of less consolidated rocks and tuffs. We will be able to do terrestrial style field geology on Mars.