Constraints on the perturbed mutual motion in Didymos due to impact-induced deformation of its primary after the DART impact

TL;DR

This study models how impact-induced deformation of Didymos's primary asteroid could alter its mutual orbit with its secondary, providing insights for the DART mission's impact effects and potential observational signatures.

Contribution

It introduces a numerical simulation approach to assess how shape deformation of the primary affects the mutual orbit after impact.

Findings

Deformation causes the orbital period to shorten.

Surface layer movement >0.4 m affects orbital and spin periods.

Shape change significantly perturbs the mutual dynamics.

Abstract

Binary near-Earth asteroid (65803) Didymos is the target of the proposed NASA Double Asteroid Redirection Test (DART), part of the Asteroid Impact & Deflection Assessment (AIDA) mission concept. In this mission, the DART spacecraft is planned to impact the secondary body of Didymos, perturbing mutual dynamics of the system. The primary body is currently rotating at a spin period close to the spin barrier of asteroids, and materials ejected from the secondary due to the DART impact are likely to reach the primary. These conditions may cause the primary to reshape, due to landslides, or internal deformation, changing the permanent gravity field. Here, we propose that if shape deformation of the primary occurs, the mutual orbit of the system would be perturbed due to a change in the gravity field. We use a numerical simulation technique based on the full two-body problem to investigate the shape effect on the mutual dynamics in Didymos after the DART impact. The results show that under constant volume, shape deformation induces strong perturbation in the mutual motion. We find that the deformation process always causes the orbital period of the system to become shorter. If surface layers with a thickness greater than ~0.4 m on the poles of the primary move down to the equatorial region due to the DART impact, a change in the orbital period of the system and in the spin period of the primary will be detected by ground-based measurement.