# Comet 67P/Churyumov-Gerasimenko rotation changes derived from sublimation induced torques

## TL;DR

This paper models how sublimation-driven torques from comet 67P/Churyumov-Gerasimenko cause observable changes in its rotation period and axis orientation, providing insights into surface activity and physical properties.

## Contribution

It introduces an analytic model linking sublimation-induced torques to rotation changes, estimating surface activity distribution and physical properties of the comet.

## Key findings

- Rotation changes constrain surface activity and sublimation rates.
- Surface active fraction distribution aligns with observed rotation data.
- Sublimation activity increases faster than insolation near perihelion.

## Abstract

(Context) The change of the rotation period and the orientation of the rotation axis of comet 67P/Churyumov-Gerasimenko (67P/C-G) is deducible from images taken by the scientific imaging instruments on-board the Rosetta mission with high precision. Non gravitational forces are a natural explanation for these data. (Aims) We describe observed changes for the orientation of the rotation axis and the rotation period of 67P/C-G. For these changes we give an explanation based on a sublimation model with a best-fit for the surface active fraction (model P). Torque effects of periodically changing gas emissions on the surface are considered. (Methods) We solve the equation of state for the angular momentum in the inertial and the body-fixed frames and provide an analytic theory of the rotation changes in terms of Fourier coefficients, generally applicable to periodically forced rigid body dynamics. (Results) The torque induced changes of the rotation state constrain the physical properties of the surface, the sublimation rate and the local active fraction of the surface. (Conclusions) We determine a distribution of the local surface active fraction in agreement with the rotation properties, period and orientation, of 67P/C-G. The torque movement confirms that the sublimation increases faster than the insolation towards perihelion. The derived relatively uniform activity pattern is discussed in terms of related surface features.