# The shape evolution of cometary nuclei via anisotropic mass loss

## TL;DR

This paper proposes a mathematical model demonstrating how anisotropic mass loss and subsurface collapse due to uneven solar exposure can transform spherical comet nuclei into bilobed shapes, explaining observed cometary morphologies.

## Contribution

It introduces a novel analytical and numerical framework linking non-uniform insolation to shape evolution of comet nuclei, providing a new explanation for bilobate forms.

## Key findings

- Explains the formation of bilobed comet nuclei through anisotropic mass loss.
- Accounts for larger light-curve amplitudes in comet nuclei compared to asteroids.
- Supports the idea that shape evolution is driven by solar irradiation patterns.

## Abstract

Context. Breathtaking imagery recorded during the European Space Agency's Rosetta mission confirmed the bilobate nature of comet 67P/Churyumov-Gerasimenko's nucleus. Its peculiar appearance is not unique among comets. The majority of cometary cores imaged at high resolution exhibit a similar build. Various theories have been brought forward as to how cometary nuclei attain such peculiar shapes. Aims. We illustrate that anisotropic mass loss and local collapse of subsurface structures caused by non-uniform exposure of the nucleus to solar irradiation can transform initially spherical comet cores into bilobed ones. Methods. A mathematical framework to describe the changes in morphology resulting from non-uniform insolation during a nucleus' spin-orbit evolution is derived. The resulting partial differential equations that govern the change in the shape of a nucleus subject to mass loss and consequent collapse of depleted subsurface structures are solved analytically for simple insolation configurations and numerically for more realistic scenarios. Results. The here proposed mechanism is capable of explaining why a large fraction of periodic comets appear to have peanut-shaped cores and why light-curve amplitudes of comet nuclei are on average larger than those of typical main belt asteroids of the same size.