Orbital period change of Dimorphos due to the DART kinetic impact

Abstract

The Double Asteroid Redirection Test (DART) spacecraft successfully performed the first test of a kinetic impactor for asteroid deflection by impacting Dimorphos, the secondary of near-Earth binary asteroid (65803) Didymos, and changing the orbital period of Dimorphos. A change in orbital period of approximately 7 min was expected if the incident momentum from the DART spacecraft was directly transferred to the asteroid target in a perfectly inelastic collision1, but studies of the probable impact conditions and asteroid properties indicated that a considerable momentum enhancement (β) was possible2,3. In the years before impact, we used lightcurve observations to accurately determine the pre-impact orbit parameters of Dimorphos with respect to Didymos4–6. Here we report the change in the orbital period of Dimorphos as a result of the DART kinetic impact to be −33.0 ± 1.0 (3σ) min. Using new Earth-based lightcurve and radar observations, two independent approaches determined identical values for the change in the orbital period. This large orbit period change suggests that ejecta contributed a substantial amount of momentum to the asteroid beyond what the DART spacecraft carried.

The Perturbed Full Two-body Problem: Application to Post-DART Didymos

“…While DART imaged the system before the impact, there are significant uncertainties in the positions of the bodies' centers of mass since the internal density distributions are unknown, which manifests in a large uncertainty in the preimpact semimajor axis. Thus, the pre-impact separation is instead measured with radar data in Thomas et al (2023). This is equal to the pre-impact semimajor axis in the circular preimpact orbit assumption.…”

“…In the first planetary defense test of a kinetic impactor, the NASA Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the secondary in the Didymos binary asteroid system, on 2022 September 26 (Daly et al 2023). The impact altered the trajectory of Dimorphos around Didymos, reducing the orbit period by around 33 minutes (Thomas et al 2023). Initial analysis of observations of the system reveals a reduction in the secondary's tangential (along-track) component of orbital velocity by about 2.7 mm s −1 (Cheng et al 2023).…”

Asteroid collision shows how much amateur astronomers have to offer

“…These skywatchers are among the authors of a study in Nature that describes how the asteroid, named Dimorphos, became temporarily brighter and redder as the spacecraft hit it 1 . One of five papers about the impact published in Nature [1][2][3][4][5] , it describes a real-time view of a cosmic collision -similar to that when Comet Shoemaker-Levy 9 slammed into Jupiter in July 1994.…”

Ejecta from the DART-produced active asteroid Dimorphos

“…Mass shedding from the surface of Dimorphos due to rotation is not likely given its slow rotation if its spin is tidally locked. But mass movement and shedding from Didymos could potentially be triggered by ejecta re-impact due to its fast rotation causing a net outward acceleration at its equator 42 , though no clear indication has been confirmed yet 3 .…”