Work

Towards a coupled activity-fallback model for comets – I. 67P/Churyumov–Gerasimenko’s water activity from a microphysics model with dynamic dust-depth

Year: 2026

Type: article

Abstract: ABSTRACT We apply a two-layer thermophysical model, with water sublimating from below a dust-crust with dynamically varying depth, to simulate the water outgassing rate, dust-ejections, and non-gravitational forces and torques of comet 67P/Churyumov–Gerasimenko. The dust-depth is determined at each time-step by the balance of dehydration and subsurface pressure, leading to alternating ejections and crust build-up. This model is the first stage of implementing a fully coupled activity-fallback model that self-consistently incorporates dust-fallback into the ejection depth calculation, but already a number of conclusions can be drawn from these results. The two-layer model with only dehydration and ejections is able to reproduce much of the Rosetta outgassing, dust-ejection data, and non-gravitational dynamics, particularly in the comet’s more primitive southern terrain. Best agreement is found for nucleus material made up of small aggregates ($d_{\mathrm{ agg}}\sim 1$ mm) with not-too-high dust-to-ice ratios ($\delta \sim 2{-}8$) and low average strengths (${\lesssim} 1$ Pa) that decreases with depth. Disagreements between the observations and model are greatest for the northern-facing and dust-covered terrains, suggesting the importance of surface modification by fallback and material processing here, which will be the subject of investigation in the next paper.

Source: Monthly Notices of the Royal Astronomical Society

DOI: 10.1093/mnras/stag1930