A change of the rotation period of asteroid (65803) Didymos caused by the DART impact

TL;DR

This study analyzed photometric data of asteroid Didymos before and after the DART impact, revealing a small but significant slowdown in its rotation period likely due to reshaping caused by the impact.

Contribution

The paper presents the first detection of a change in Didymos's primary rotation period resulting from the DART impact, using extensive light curve analysis and shape modeling.

Findings

Detected a 0.18-second increase in Didymos's rotation period after impact.

Confirmed the impact caused reshaping, making Didymos more oblate.

Demonstrated the effectiveness of light curve analysis in monitoring asteroid physical changes.

Abstract

On 26 September 2022, the NASA Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the secondary component of the binary asteroid (65803)~Didymos. This experiment tested the Kinetic Impactor technology for diverting dangerous asteroids. Due to the impact, the binary system's angular momentum has changed, resulting in a significant change in the orbital period of Dimorphos. Precise values of the pre- and post-impact orbital periods were derived from a large set of photometric light curves measured for the Didymos-Dimorphos system during six apparitions from 2003 to 2023. We used these data to detect a possible change in the rotation period of the primary as a consequence of the impact. We analyzed the binary system's light curves using the binary asteroid light curve decomposition method. We selected parts of the light curves covering orbital phases outside mutual events, which represent the primary rotational light curves. We applied the light curve inversion method to construct a convex shape model of Didymos and determine its rotation period before and after the impact. These two periods were treated as independent free parameters of the modeling. We found a value of 2.2603891 +/- 0.0000002 h for the pre-impact period and 2.260440 +/- 0.000008 h for the post-impact period. Their difference 0.18 +/- 0.03 s is small yet significant, indicating that the rotation of Didymos became slower after the DART impact. The most plausible physical explanation is Didymos's post-impact reshaping, making its shape more oblate.