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

Abstract

Abstract On 2022 September 26, 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 systems period. We present new data from the Thacher Observatory and measure a change in period, ΔP = − 34.2 ± 0.1 minutes, which deviates from previous measurements by 3.5σ. This suggests that the system period may have decreased by ∼1 minute in the 20–30 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.