Water Ice Exposure Mechanism on the Surface of Comet 67P/Churyumov-Gerasimenko (Supplementary material)

Description

Abstract

Bright features on comet nuclei are associated with the temporary exposure of volatiles due to surface erosion or frost deposition. Earlier studies have shown that their composition is mainly linked to water ice, with carbon dioxide identified in one specific area. The presence of volatile exposure indicates surface erosion and inhomogeneity in the nuclear material. Morphological and spatial analysis of the OSIRIS dataset is used to identify the time-series evolution of bright spots and the nature of their formation on comet 67P. The results of surface analysis revealed 340 ice-exposed locations, including 114 unique locations that had not been previously reported. The time-series analysis confirmed the cycling mechanism of exposure and activity persistence at substantial heliocentric distances, with the process intensifying near perihelion. Our study elucidates the mechanism of water-ice erosional exposure through heat- and mass-transfer models. Two dominant scenarios were considered as the primary formation mechanisms: (a) Continuous Erosion and (b) Cyclic Surface Erosion. The considered scenarios were applied to describe several types of bright spots: areal volatile exposure in a smooth material and volatile exposure in consolidated material, including consolidated material and separated boulders. It was found that neither mechanism alone can fully explain the diversity of observed exposures. It was found that neither mechanism alone can fully explain the observed diversity of exposures, and it is likely a combination of mechanisms. In materials with high volatile concentrations, it is assumed that the predominant mechanism is Continuous Erosion. In contrast, in materials with lower volatile concentrations or non-uniform structures, dry crust formation and its destruction can be presumed during Cyclic Surface Erosion.