DEGRADATION OF ENDEAVOUR CRATER BASED ON ORBITAL AND ROVER-BASED OBSERVATIONS

Endeavour is a ~22 km diameter Noachian age crater that has been extensively eroded and then embayed by younger Burns formation sulfate-rich sandstones. The Opportunity rover has been exploring Endeavour’s western rim segments since 2011, complemented by an extensive array of orbital data over the traverse areas. Impact crater densities suggest the nearby ~19 km diameter Bopolu crater is on the order of 0.5 billion years younger than Endeavour, but has experienced much less degradation, showing steeper and more rugged walls. By way of contrast, Endeavour’s rim segments have been rounded by erosion, with pediment-like surfaces extending to the interior and exterior of the rim crests. Endeavour clearly experienced an early period of extensive erosion before Bopolu was formed. Results from the MARSSIM landscape evolution model show that Bopolu can be degraded to a similar state as Endeavour through early fluvial and diffusive mass wasting processes, with lacustrine deposits forming in the interior. The Perseverance valley system (PVS) is superimposed on Endeavour’s Cape Byron eroded and rounded rim segment, although PVS must still be an ancient system, given that several small craters are superimposed on its channels. PVS may record the waning stages of early degradation at Endeavour, forming by overflow of a lake located to the west of the rim, thereby generating the shallow channels west of the rim and an anastomosing channel system cutting downhill into the crater. A key issue with this scenario is that the western plains tilt ~0.8˚ away from the rim and do not form a catchment. Using an exponentially decreasing elevation of Endeavour’s original, degraded rim and ejecta deposit, Athy’s Law for sediment compaction scaled for Mars gravity, and an appropriate mix of deep mudstones and shallow sandstones, we find that embaying Burns formation would have led to a catchment before gravitationally-induced compaction. This result does not prove that PVS was a fluvial system and observations from Opportunity as it descends the PVS will provide key data to support or refute a fluvial mechanism, as opposed to processes that involve debris flows, ice, and/or wind, or some more complicated set of processes, perhaps involving fluvial action.