Cliff collapse on Comet 67P/Churyumov-Gerasimenko -- II. Imhotep and Hathor

TL;DR

This study uses MIRO observations to analyze cliff collapses on comet 67P, revealing detailed properties of near-surface materials, including stratification, ice content, and physical characteristics, providing insights into comet surface processes.

Contribution

It presents the first detailed thermophysical analysis of collapsed cliffs on comet 67P, constraining subsurface composition and stratification through microwave observations.

Findings

Imhotep has a dust/ice mixture with sublimating CO2 ice 11 cm below surface.

Hathor has a thin dust mantle with no detectable CO2 ice within 1 meter.

Hathor's mantle density suggests compression has occurred.

Abstract

Cliff collapses on Comet 67P/Churyumov-Gerasimenko expose relatively pristine nucleus matter and offer rare opportunities to characterise ice-rich comet material. Here, Microwave Instrument for \emph{Rosetta} Orbiter (MIRO) observations of two collapsed or crumbling cliffs in the Imhotep and Hathor regions have been assembled. The empirical diurnal antenna temperature curves are analysed with thermophysical and radiative transfer models in order to place constraints on the physical properties and degrees of stratification in the near-surface material. The Imhotep site consists of an exposed dust/water-ice mixture with thermal inertia 100-$160\,\mathrm{J\,m^{-2}\,K^{-1}\,s^{-1/2}}$, having sublimating $\mathrm{CO_2}$ ice located $11\pm 4\,\mathrm{cm}$ below the surface. Its estimated age is consistent with an outburst observed on 2014 April 27-30. The Hathor site has a $0.8\pm 0.2\,\mathrm{cm}$ dust mantle, a thermal inertia of $40\pm 20\,\mathrm{J\,m^{-2}\,K^{-1}\,s^{-1/2}}$, no $\mathrm{CO_2}$ ice to within $1.0\,\mathrm{m}$ depth, and a mantle bulk density of $340\pm 80\,\mathrm{kg\,m^{-3}}$ that is higher than the theoretically expected $180\pm 10\,\mathrm{kg\,m^{-3}}$, suggesting that compression has taken place.