Thermal Shadows and Compositional Structure in Comet Nuclei

TL;DR

This study uses a 3D thermal model to show how surface albedo variations create thermal shadows and compositional gradients in comet nuclei, affecting their evolution over millions of years.

Contribution

It demonstrates that non-uniform surface albedo causes long-lasting thermal and compositional structures in comets, influenced by obliquity, thermal conductivity, and heliocentric distance.

Findings

Thermal shadows lead to strong lateral thermal gradients.

Compositional gradients can persist for over 10 million years.

Non-uniform structures can form during comet evolution, not just from initial formation.

Abstract

We use a fully 3-dimensional thermal evolution model to examine the effects of a non-uniform surface albedo on the subsurface thermal structure of comets. Surface albedo markings cast "thermal shadows", with strong lateral thermal gradients. Corresponding compositional gradients can be strong, especially if the crystallization of amorphous water ice is triggered in the hottest regions. We show that the spatial extent of the structure depends mainly on the obliquity, ther- mal conductivity and heliocentric distance. In some circumstances, subsurface structure caused by the thermal shadows of surface features can be maintained for more than 10 Myr, the median transport time from the Kuiper Belt to the inner solar system. Non-uniform compositional structure can be an evolutionary product and does not necessarily imply that comets consist of building blocks accumulated in different regions of the protoplanetary disk.