The NASA Double Asteroid Redirection Test (DART) spacecraft successfully impacted the Didymos-Dimorphos binary asteroid system on 2022 September 26 UTC. We provide an update to its pre-impact mutual orbit and estimate the post-impact physical and orbital parameters, derived using ground-based photometric observations taken from July 2022 to February 2023. We found that the total change of the orbital period was −33.240±0.072 min. (all uncertainties are 3σ). We obtained the eccentricity of the post-impact orbit to be 0.028±0.016 and the apsidal precession rate of 7.3±2.0 deg./day from the impact to 2022 December 2. The data taken later in December to February suggest that the eccentricity dropped close to zero or the orbit became chaotic approximately 70 days after the impact. Most of the period change took place immediately after the impact but in a few weeks following the impact it was followed by additional change of −27−58+19 seconds or −19±18 seconds (the two values depend on the approach we used to describe the evolution of the orbital period after the impact -- an exponentially decreasing angular acceleration or an assumption of a constant orbital period, which changed abruptly some time after the impact, respectively). We estimate the pre-impact Dimorphos-Didymos size ratio was 0.223±0.012 and the post-impact is 0.202±0.018, which indicates a marginally significant reduction of Dimorphos' volume by (9±9)% as the result of the impact.
@article{arxiv.2403.02804,
title = {Dimorphos orbit determination from mutual events photometry},
author = {Peter Scheirich and Petr Pravec and Alex J. Meyer and Harrison F. Agrusa and Derek C. Richardson and Steven R. Chesley and Shantanu P. Naidu and Cristina Thomas and Nicholas A. Moskovitz},
journal= {arXiv preprint arXiv:2403.02804},
year = {2024}
}