Modeling of comet water production

II. Dust layer removal model: The case of 67P/Churyumov-Gerasimenko

¹ Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, PR China
² School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, PR China
³ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
⁴ Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany
⁵ European Space Agency (ESA), ESAC, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain

^★ Corresponding author: zhaoyuhui@pmo.ac.cn

Received: 10 June 2025
Accepted: 24 September 2025

Abstract

Aims. This study aims to simulate the dynamic evolution of a cometary surface using a dust layer removal model we first proposed in our previous work. There is a focus on understanding the microphysical mechanisms driving localized activity and validating the model using inversion results derived from observations.

Methods. We implemented a dynamic model within the mass-loss-driven shape evolution model framework that switches between a pure-ice sublimation model and a two-layer thermophysical model, depending on whether the gas pressure exceeds the tensile strength of the dust layer. Using the shape model of comet 67P/Churyumov-Gerasimenko, we simulated the accumulation and ejection of dust over a full orbit and systematically investigated the effects of porosity, dust particle size, and initial layer thickness on sublimation-driven activity.

Results. The model qualitatively reproduces cycling dust removal activities triggered by subsurface gas pressure buildup. The results indicate the dust layer removal exhibits periodic evolution, representing a general behavior that is independent of the dust layer thickness at aphelion. Higher porosity and larger dust particle sizes enhance the permeability and reduce the tensile strength of the dust layer, thereby promoting more frequent dust removal activities. The model qualitatively fits the effective active fraction curves and distributions derived from observations, and we identify a feasible parameter space that reproduces these trends. Our preliminary estimates indicate that even with an overestimated contribution of dust fallout, our model remains physically consistent and supports the plausibility of dust layer removal.

Conclusions. The model captures both the temporal variability and spatial heterogeneity of cometary activity, offering a physically consistent explanation for observed variations in water production and nongravitational effects across different times and surface regions. This approach holds promise for future applications in the nongravitational forces’ inversion and the study of surface evolution. Incorporating a higher spatial resolution and additional physical processes, such as dust fallback, self-heating, and gravity, is essential for improving the model’s accuracy in regulating activity and shaping the near-surface environment.