RECONSTRUCTING THE PALEOLACUSTRINE HISTORY OF SOUTHWESTERN MELAS CHASMA TO PROVIDE GEOLOGIC CONTEXT FOR FUTURE MARS ROVER EXPLORATION (Invited Presentation)

Along the wallrock in southwestern Melas Chasma is an enclosed 30 km x 120 km basin perched 1 km above the Valles Marineris canyon floor. Eleven fan-shaped landforms within the basin record various depositional environments ranging from subaerial to shallow subaqueous to deep subaqueous emplacement. A distinctive megaripple marker bed, with inferred indurated aeolian bedforms, is within the stratigraphic record of presumed lacustrine deposits, and is interpreted to demarcate a minimum of two lake highstands. Tributary drainage pattern in the western valley network changed from a dendritic to a meandering system, recording a shift in fluvial activity that is also consistent with fluctuating lake levels. Landform scale was used to estimate average discharge (~30 m3/s), formative discharge (200–300 m3/s), and fan formation timescale, which further inform the duration of lacustrine activity within the basin. Climate conditions conducive to lake stability had to be maintained for a duration long enough to construct these fans over periods of at least centuries to millennia during the Late Hesperian to Early Amazonian.

Southwest Melas Chasma is one of eight candidate landing sites for NASA’s 2020 Mars rover undergoing detailed characterization studies as part of the landing site evaluation process. This basin is an ideal exploration zone for the mission with the high biosignatures preservation potential of lacustrine deposits, the excellent stratigraphic exposure and well defined geologic context. The 2020 rover has the capability to drill and cache samples for future return to Earth. Traverse distances between regions of interest are short (few km). During a nominal primary mission, the rover can collect samples from the rich aqueous history as well as hydrated silica outcrops (identified in CRISM spectra, but of unknown origin), yielding a diversity of scientifically rich specimens for further detailed study in terrestrial labs. With over 90% of the landing ellipse mapped as high priority region of interests, the mission will be devoted to hypothesis testing using the instrument payload, rather than driving to science targets. Adding daughter payloads, such as MarsDrop, increases ground based observations (e.g., surface images, methane measurements) at additional landing sites.