Bedrock Chute Formation by Dry Rockfall in Endeavour Crater, Mars

Abstract Degradation of crater topography is important on planetary surfaces as it can record environmental conditions through rates and processes of erosion. Regolith creep is classically thought to dominate crater wall degradation, leading to smooth crater walls. Processes that create rough topography, such as chutes and alcoves, are often attributed to volatiles. Here we explore an alternate hypothesis for chute formation by erosion from dry rockfall. We mapped the western rim of Endeavour crater, Mars, including the Marathon and Perseverance valleys visited by NASA's Mars Exploration Rover (MER) Opportunity. Marathon Valley is a broad alcove with locally steep, rubbly outcrops, a moderately sloping (18°) bedrock floor dissected by a network of shallow grooves and boulders downslope. When initiated from these steep (>45°) outcrops, rockfall modeling shows focused impacts near the headwall of Marathon Valley and rocks that traverse the valley floor even at gradients below the angle of repose. Perseverance Valley is a smaller chute with relief that is too subtle to be captured in the digital elevation model, and therefore the model does not produce funneled rockfall there. Across the Endeavour crater rim, the rockfall‐erosion hypothesis is consistent with locally steep rock outcrops as rockfall sources, boulder fields, and the rough chute‐and‐spur topography. We propose that through topographic steering, rockfall can be funneled into chutes and alcoves, concentrating impacts and erosion there, and further developing these landforms in the absence of flowing water.