Momentum transfer from the DART mission kinetic impact on asteroid Dimorphos

The NASA DART mission performed a kinetic impact on asteroid Dimorphos, the satellite of (65803) Didymos, at 23:14 UTC on 26 September 2022 to test planetary defence. This first hypervelocity impact at relevant size and velocity scales aimed to validate kinetic impact as a deflection method. We determine the momentum transferred to Dimorphos by the impact. From the measured change in the binary orbit period, we find an instantaneous reduction in Dimorphos’s along-track orbital velocity of 2.70 ± 0.10 mm s−1, indicating enhanced momentum transfer due to recoil from impact ejecta. For a Dimorphos bulk density between 1,500 and 3,300 kg m−3, the expected momentum enhancement factor β ranges from 2.2 to 4.9, depending on Dimorphos’s mass. Assuming Dimorphos and Didymos have equal densities of 2,400 kg m−3, β = 3.6+0.13−0.10 (1σ). These β values show that escaping ejecta contributed substantially more momentum than the incident spacecraft, demonstrating that the DART kinetic impact effectively deflected Dimorphos.

Andrew F. Cheng, Harrison F. Agrusa, Brent W. Barbee, Alex J. Meyer, Tony L. Farnham, Sabina D. Raducan, Derek C. Richardson, Elisabetta Dotto, Angelo Zinzi, Vincenzo Della Corte, Thomas S. Statler, Steven Chesley, Shantanu P. Naidu, Masatoshi Hirabayashi, Jian-Yang Li, Siegfried Eggl, Olivier S. Barnouin, Nancy L. Chabot, Sidney Chocron, Gareth S. Collins, R. Terik Daly, Thomas M. Davison, Mallory E. DeCoster, Carolyn M. Ernst, Fabio Ferrari, Dawn M. Graninger, Seth A. Jacobson, Martin Jutz, Kathryn M. Kumamoto, Robert Luther, Joshua R. Lyzhoft, Patrick Michel, Naomi Murdoch, Ryota Nakano, Eric Palmer, Andrew S. Rivkin, Daniel J. Scheeres, Angela M. Stickle, Jessica M. Sunshine, Josep M. Trigo-Rodriguez, Jean-Baptiste Vincent, James D. Walker, Kai Wünnemann, Yun Zhang, Marilena Amoroso, Ivano Bertini, John R. Brucato, Andrea Capannolo, Gabriele Cremonese, Massimo Dall'Ora, Prasanna J. D. Deshapriya, Igor Gai, Pedro H. Hasselmann, Simone Leva, Gabriele Impresario, Stavro L. Ivanovski, Michèle Lavagna, Alice Lucchetti, Elena M. Epifani, Dario Modenini, Maurizio Pajola, Pasquale Palumbo, Davide Perna, Simone Pirrotta, Giovanni Poggiali, Alessandro Rossi, Paolo Tortora, Marco Zannoni, Giovanni Zanotti