Asteroid modelling by starlight diffraction: The shape of Dimorphos, the satellite of (65803) Didymos

TL;DR

This study uses stellar occultation diffraction data to model and constrain the shape and size of Dimorphos, revealing an equatorially elongated post-impact shape consistent with recent findings.

Contribution

First use of simultaneous diffraction signatures from multiple occultation chords to model asteroid shape, providing new constraints on Dimorphos' post-impact geometry.

Findings

Projected shape well constrained and consistent with recent data

Extended 3D model suggests equatorially elongated shape

Diffraction data effectively constrains asteroid morphology

Abstract

The DART spacecraft impacted Dimorphos, the satellite of (65803) Didymos, in September 2022. Evidence of crater formation and possible global reshaping has been obtained indirectly from spacecraft and ground-based data. Since the impact, several stellar occultations by Didymos have been observed, but only one in particular, on January 21, 2023, can provide useful constraints on the size and shape of Dimorphos. We modelled the diffraction signatures recorded on multiple occultation chords to constrain the projected shape and size of Dimorphos, assuming an ellipsoidal model. This is the first time diffraction observed simultaneously on several chords of a single event has been used for such a purpose. The projected shape at the epoch of the event is well constrained and consistent with recent post-DART determinations. When extended to a full three-dimensional ellipsoidal solution, the result remains compatible with previous studies, suggesting an equatorially elongated post-impact shape.