ASTERIA -- Thermal Inertia Evaluation of asteroid Didymos

TL;DR

This study estimates the pre-impact thermal inertia of asteroid Didymos using ASTERIA, providing insights into surface alterations post-DART impact and suggesting that near-Earth asteroids have lower thermal inertia than previously thought.

Contribution

It introduces ASTERIA as an alternative method to thermophysical modeling for estimating asteroid thermal inertia through orbital drift analysis.

Findings

Estimated Didymos thermal inertia: 211-258 J m$^{-2}$ K$^{-1}$ s$^{-1/2}$

Results align with previous data, supporting lower thermal inertia in near-Earth asteroids

Robust estimates confirmed against variations in physical parameters

Abstract

Asteroid Didymos, recently targeted by the NASA DART mission, is also planned to be visited by the ESA Hera mission. The main goal of the DART mission was to impact Dimorphos, the small satellite of Didymos, which was accomplished in September 2022. This collision altered the Didymos-Dimorphos system, generating a notable quantity of ejecta that turned Dimorphos into an active asteroid, with some ejecta potentially settling on the surfaces of both components. This prompts the investigation into the extent of post-impact surface alterations on these bodies compared to their original states. The purpose of this study is to evaluate the pre-impact thermal inertia of Didymos independently. We employed ASTERIA, an alternative to conventional thermophysical modeling, to estimate the surface thermal inertia of Didymos. The approach is based on a model-to-measurement comparison of the Yarkovsky effect-induced drift on the orbital semi-major axis. These results, alongside existing literature, enable an evaluation of the impact-induced alterations in Didymos's thermal inertia. Our nominal estimate with a constant thermal inertia model stands at $\Gamma = 211_{-55}^{+81}$ J m$^{-2}$ K$^{-1}$ s$^{-1/2}$, while assuming it varies with the heliocentric distance with an exponent of $-0.75$ thermal inertia of Didymos is found to be $258_{-63}^{+94}$ J m$^{-2}$ K$^{-1}$ s$^{-1/2}$. Subsequent verification confirmed that this result is robust against variations in unknown physical parameters. The thermal inertia estimates for Didymos align statistically with values reported in the literature, derived from both pre- and post-impact data. The forthcoming Hera mission will provide an opportunity to corroborate these findings further. Additionally, our results support the hypothesis that the thermal inertia of near-Earth asteroids is generally lower than previously expected.