THE FILLING OF ENDEAVOUR CRATER, MARS: A MODELING APPROACH TO UNDERSTANDING HiRISE, CRISM, AND OPPORTUNITY OBSERVATIONS

Endeavour Crater, a partially sediment-filled crater within Meridiani Planum, is an important test-bed for hypotheses of the origin of the Meridiani deposits. The present-day crater is ~20 km wide and ~500 m deep, and encloses an asymmetric sedimentary mound. Despite significant erosion of these deposits, much of the present-day sediment surface around Endeavour appears to be a primary depositional surface. In the context of the playa hypothesis for the origin of the Meridiani deposits, this surface would represent the paleo-water table. HiRISE stereo-topography reveals that the sediment surface approaching Endeavour dips steeply inwards, forming a smooth and continuous slope into the crater, interrupted by occasional outcrops of phyllosilicate-bearing rim material. In addition, the plains surrounding the crater are marked by two distinct crater populations: low relief eroded craters interpreted as post-dating the depositional period, and older inverted craters visible both from orbital and rover observations. This study uses hydrological models to investigate the sedimentary filling of Endeavour Crater. Groundwater upwelling and evaporitic cementation of sediments reproduces the unique topography of the sediment surface for cases in which the permeability of the sediments is significantly less than that of the ancient regolith beneath. As a result of the diffusive nature of groundwater flow, the sediment surface follows a smoothed representation of the underlying pre-sediment topography - following the long-wavelength shape of the crater, while smoothing over the short-wavelength relief of the rim. The required low permeability of the sediments is consistent with their heavily cemented nature in microscopic imager observations. Inversion of the small craters formed during the period of active deposition would result from the increase in permeability below the crater floors, allowing an enhanced flux of groundwater to the surface. Continued numerical modeling in concert with remote sensing and in situ observations will shed light on both the origin of these deposits, and their implications for the hydrology and climate of Mars at the time.