New Post-DART Collision Period for the Didymos System: Evidence for Anomalous Orbital Decay

TL;DR

This paper reports a significant, unexpected decrease in the orbital period of the Didymos asteroid system following the DART impact, suggesting anomalous orbital decay not explained by existing models.

Contribution

It provides new observational evidence of an unexplained orbital period decrease in the Didymos system after DART impact, challenging current understanding of post-impact dynamics.

Findings

Measured a 1-minute decrease in orbital period post-impact

Observed a deviation from previous measurements by 3.5 sigma

Concluded that known mechanisms cannot explain the period change

Abstract

On September 26, 2022, NASA's DART spacecraft impacted Dimorphos, the secondary asteroid in the (65803) Didymos system, so that the efficiency with which a satellite could divert an asteroid could be measured from the change in the system's period. We present new data from the Thacher Observatory and measure a change in period, $\Delta P = -34.2 \pm 0.1$ min, which deviates from previous measurements by $3.5\,\sigma$. This suggests that the system period may have decreased by $\sim 1$ minute in the 20 to 30 days between previous measurements and our measurements. We find that no mechanism previously presented for this system can account for this large of a period change, and drag from impact ejecta is an unlikely explanation. Further observations of the (65803) Didymos system are needed to both confirm our result and to further understand this system post impact.