Modeling of comet water production

I. Sensitivity to macro- and micro-model parameters

¹ Key Laboratory of Planetary Sciences, 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 authors; skorov@mps.mpg.de; zhaoyuhui@pmo.ac.cn

Received: 4 September 2024
Accepted: 19 November 2024

Abstract

Aims. This study investigates the impact of microscopic and macroscopic cometary surface properties on water production variations with heliocentric distance, focusing on dust layer thickness, grain size, nucleus shape, and spin axis orientation.

Methods. We employed a two-layer thermophysical model to calculate effective gas production, incorporating a dust layer of porous aggregates of submillimeter- and millimeter-sized grains. The model includes radiative thermal conductivity and permeability for volatile diffusion and considers dust layer evolution and tensile strength. We examined different cometary nucleus shape models based on spacecraft observations and calculated power-law exponents for water production rates as functions of heliocentric distance.

Results. A two-layer outgassing model with fixed layer properties showed minimal qualitative differences from a simpler water ice sublimation model. The study reaffirms the critical role of the spin axis inclination and illuminated cross-section variation with the heliocentric distance in gas production. Using 67P/Churyumov-Gerasimenko’s orbital parameters, the study demonstrates that dust accumulation and layer growth significantly alter production rate exponents. Additionally, considering tensile strength in a homogeneous spherical nucleus model revealed the potential for local dust crust removal near perihelion.

Conclusions. Macroscopic properties such as nucleus shape and spin axis orientation significantly influence water production rate variations with heliocentric distance. Microscopic surface characteristics and dust layer growth also play crucial roles in cometary activity. Incorporating tensile strength and dust removal mechanisms into models provides a more accurate representation of comet activity, particularly near perihelion. This refined model enhances our understanding of comet outgassing, highlighting the importance of detailed surface property data for an accurate interpretation of observations.