Pits formation from volatile outgassing on 67P/Churyumov-Gerasimenko

TL;DR

This study models the thermal evolution of comet 67P/Churyumov-Gerasimenko's subsurface, showing how volatile processes can form pits within the comet's lifetime, influenced by dust mantle presence and porosity.

Contribution

It provides a detailed simulation-based analysis of pit formation mechanisms on 67P, emphasizing the roles of clathrate destabilization, ice crystallization, and subsurface porosity.

Findings

Pits can form via sinkholes or outbursts within the comet's lifetime.

Dust mantle presence affects sublimation and outgassing behavior.

Subsurface is heterogeneous at 100-200 meters scale.

Abstract

We investigate the thermal evolution of comet 67P/Churyumov-Gerasimenko's subsurface in the Seth_01 region, where active pits have been observed by the ESA/Rosetta mission. Our simulations show that clathrate destabilization and amorphous ice crystallization can occur at depths corresponding to those of the observed pits in a timescale shorter than 67P/Churyumov-Gerasimenko's lifetime in the comet's activity zone in the inner solar system. Sublimation of crystalline ice down to such depths is possible only in the absence of a dust mantle, which requires the presence of dust grains in the matrix small enough to be dragged out by gas from the pores. Our results are consistent with both pits formation via sinkholes or subsequent to outbursts, the dominant process depending on the status of the subsurface porosity. A sealed dust mantle would favor episodic and disruptive outgassing as a result of an increasing gas pressure in the pores, while a high porosity should allow the formation of large voids in the subsurface due to the continuous escape of volatiles. We finally conclude that the subsurface of 67P/Churyumov-Gerasimenko is not uniform at a spatial scale of 100-200~m.