Thermal Tomography of Asteroid Surface Structure

TL;DR

This paper develops a method to estimate asteroid surface thermal inertia, revealing it increases with depth and spin period, which impacts understanding of asteroid surface properties and planetary defense strategies.

Contribution

It introduces a new approach to estimate thermal inertia of asteroids and demonstrates its variation with depth and spin period, providing insights into surface structure and implications for orbit prediction.

Findings

Thermal inertia increases with asteroid spin period.

Thermal inertia rises rapidly within the top 10 cm of surface.

Results impact models of the Yarkovsky effect and planetary defense.

Abstract

Knowledge of the surface thermal inertia of an asteroid can provide insight into surface structure: porous material has a lower thermal inertia than rock. We develop a means to estimate thermal inertia values of asteroids and use it to show that thermal inertia appears to increase with spin period in the case of main-belt asteroids (MBAs). Similar behavior is found on the basis of thermophysical modeling for near-Earth objects (NEOs). We interpret our results in terms of rapidly increasing material density and thermal conductivity with depth, and provide evidence that thermal inertia increases by factors of 10 (MBAs) to 20 (NEOs) within a depth of just 10 cm. Our results are consistent with a very general picture of rapidly changing material properties in the topmost regolith layers of asteroids and have important implications for calculations of the Yarkovsky effect, including its perturbation of the orbits of potentially hazardous objects and those of asteroid family members after the break-up event. Evidence of a rapid increase of thermal inertia with depth is also an important result for studies of the ejecta-enhanced momentum transfer of impacting vehicles ("kinetic impactors") in planetary defense.