Degradation of rocks on the Moon: Insights on abrasion from topographic diffusion, LRO/NAC and Apollo images

Abstract

The efficiency of regolith production is key in understanding the properties of airless surfaces. Debris aprons, of fillets, around rocks are a ubiquitous morphology on many surfaces without atmosphere, which origin and evolution are largely unknown. Here we develop a model for the morphological evolution of the rock-fillet system on the Moon that considers fillet material to be produced by the juxtaposed rock under abrasion. We show that rocks of different cohesion have fillets with distinct morphological evolution. Thus, a fillet around a rock allows to disentangle rock cohesion from its surface exposure age. By combing topographic diffusion modeling with images of blocks of known age on the Moon, we find abrasion rates for m–sized rocks to be higher than for cm–sized rocks. Artificial images constructed with model topography indicate that rocks with fillet can be identified in orbital images by a bright halo around a rock and by the fillet shadows. Fillets around lunar rocks are consistent with abrasion by isotropic micrometeoroid bombardment.