The fillet of a rock on the Moon: Cohesion and size dependent abrasion rates from topographic diffusion, LRO/NAC and Apollo images

TL;DR

This study investigates how rock cohesion and size influence abrasion rates on the Moon, using topographic modeling and lunar images to reveal insights into regolith production and surface evolution.

Contribution

It introduces a method to estimate rock cohesion and abrasion rates from fillet morphology, linking surface features to physical properties and exposure age.

Findings

Abrasion rates for cm-sized boulders are around 0.2 mm/Myr.

For 10-m sized blocks, abrasion rates are approximately 20 mm/Myr.

Higher strength rocks exhibit about 50% reduced abrasion rates.

Abstract

The efficiency of regolith production is key in understanding the properties of airless surfaces. Debris aprons, of fillets, around rocks are an ubiquitous morphology on many surfaces without atmosphere, which origin and evolution are largely unknown. Here we show that fillet originates from the juxtaposed rock under abrasion and 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 cm-sized boulders similar to regional rates (0.2 mm/Myr), whereas for 10-m sized blocks the rate is two order of magnitude higher (20 mm/Myr). Rates for instances of rocks of higher strength are reduced by ~50%. Fillets around lunar rocks are consistent with abrasion by isotropic micrometeoroid bombardment.