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.

Astronomical Institute of the Czech Academy of Sciences Ondřejov Czech Republic

Cardiff University Cardiff UK

Carnegie Institution for Science Las Campanas Observatory La Serena Chile

Green Bank Observatory Green Bank WV USA

Isfahan University of Technology Isfahan Iran

Jet Propulsion Laboratory California Institute of Technology Pasadena CA USA

Johns Hopkins University Applied Physics Laboratory Laurel MD USA

Las Cumbres Observatory Goleta CA USA

Lowell Observatory Flagstaff AZ USA

Magdalena Ridge Observatory New Mexico Institute of Mining and Technology Socorro NM USA

National Radio Astronomy Observatory Charlottesville VA USA

Niels Bohr Institute University of Copenhagen Copenhagen Denmark

Northern Arizona University Flagstaff AZ USA

Seoul National University Gwanak gu Seoul Korea

SETI Institute Mountain View CA USA

United States Naval Academy Annapolis MD USA

Universidad Católica de la Santísima Concepción Concepción Chile

Universidad de Antofagasta Antofagasta Chile

Universität Hamburg Hamburg Germany

University of California Santa Barbara Santa Barbara CA USA

University of Edinburgh Royal Observatory Edinburgh UK

University of Maryland College Park MD USA

University of St Andrews St Andrews UK

University of Washington Seattle WA USA

Nature. 2023 Apr;616(7957):437-438. doi: 10.1038/d41586-023-01020-1. PubMed

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Successful kinetic impact into an asteroid for planetary defence

Ejecta from the DART-produced active asteroid Dimorphos