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

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.

Automated summary

Understanding the properties and evolution of airless surfaces is important, and the efficiency of regolith production plays a key role in this. We developed a model to study the morphological evolution of the rock-fillet system on the Moon, and found that different cohesive rocks have distinct morphological evolution of fillets. This allows us to distinguish rock cohesion from its surface exposure age by examining the fillet around a rock. Combining topographic diffusion modeling with images of known age rocks, we determined that the abrasion rate for m-sized rocks is higher than for cm-sized rocks. Our findings suggest that fillets around lunar rocks are a result of isotropic micrometeoroid bombardment.