Thermal environment and erosion of comet 67P/Churyumov-Gerasimenko

¹ Aix Marseille Univ, CNRS, CNES, Laboratoire d’Astrophysique de Marseille, Marseille, France
² Instituto de Astrofísica de Andalucía - CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
³ Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany
⁴ Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, USA
⁵ DLR Institut für Planetenforschung, Rutherfordstraße 2, 12489 Berlin, Germany
⁶ Institute for Theoretical Physics, Johannes Kepler University Linz, Austria
⁷ Alma Mater Studiorum - Università di Bologna, Dipartimento di Ingegneria Industriale, Via Fontanelle 40, 47121 Forlì, Italy
⁸ Zuse Institute Berlin, 14195 Berlin, Germany
⁹ CNRS, Laboratoire J.-L. Lagrange, Observatoire de la Côte d’Azur, Boulevard de l’Observatoire, CS 34229 - 06304 Nice Cedex 4, France

^★ Corresponding author; olivier.groussin@lam.fr

Received: 16 September 2024
Accepted: 12 December 2024

Abstract

Aims. This paper focuses on how insolation affects the nucleus of comet 67P/Churyumov-Gerasimenko over its current orbit. We aim to better understand the thermal environment of the nucleus, in particular its surface temperature variations, erosion, relationship with topography, and how insolation affects the interior temperature for the location of volatile species (H₂O and CO₂).

Methods. We have developed two thermal models to calculate the surface and subsurface temperatures of 67P over its 6.45-year orbit. The first model, with high resolution (300 000 facets), calculates surface temperatures, taking shadows and self-heating into account but ignoring thermal conductivity. The second model, with lower resolution (10 000 facets), includes thermal conductivity to estimate temperatures down to ~3 m below the surface.

Results. The thermal environment of 67P is strongly influenced by its large obliquity (52°), which causes significant seasonal effects and polar nights. The northern hemisphere is the coldest region, with temperatures of 210–300 K. H₂O is found in the first few centimetres, while CO₂ is found deeper (~2 m) except during polar night around perihelion, when CO₂ accumulates near the surface. Cliffs erode 3–5 times faster than plains, forming terraces. The equatorial region receives maximum solar energy (8.5×10⁹ J m⁻² per orbit), with maximum surface temperatures of 300–350 K. On the plains, H₂O is found in the first few centimetres, while CO₂ is found deeper (~2 m) and never accumulates near the surface. In the southern hemisphere, a brief intense perihelion heating raises temperatures to 350–400 K, which is followed by a 5-year polar night when surface temperatures drop to 55 K. Here H₂O remains in the first few centimetres, while CO₂ accumulates shallowly during polar night, enriching the region. Erosion is maximal in the southern hemisphere and concentrated on the plains, which explains the observed overall flatness of this hemisphere compared to the northern one. Over one orbit, the total energy from self-heating is 17% of the total energy budget, and 34% for thermal conduction. Our study contributes to a better understanding of the surface changes observed on 67P.