Rahil Makadia, Steven R. Chesley, David Herald, Davide Farnocchia, Nancy Chabot, Shantanu P. Naidu, Andrew S. Rivkin, Alexandros Siakas, D. Souami, Paolo Tanga, Sotirios Tsavdaridis, Kleomenis Tsiganis, Sébastien Bouquillon, Siegfried Eggl
In September 2022, NASA's Double Asteroid Redirection Test (DART) spacecraft crashed into Dimorphos and demonstrated the kinetic impact method of protecting Earth from asteroids. A fraction of the impulse delivered to Dimorphos was also imparted onto the Didymos system's barycenter, changing its heliocentric orbit. Here, we present the first-ever measurement of human-caused change in the heliocentric orbit of a celestial body. Thanks to stellar occultation and radar measurements, we estimate that the Didymos system experienced an along-track velocity change of -11.7 ± 1.3 micrometers per second. We constrain the heliocentric momentum enhancement factor for DART at 2.0 ± 0.3 and the bulk densities of Didymos and Dimorphos at 2600 ± 140 and 1540 ± 220 kilograms per cubic meter, respectively. Our results demonstrate that targeting the secondary asteroid in binary systems constitutes a possible strategy for kinetic impact deflection, adding to humanity's planetary defense capabilities.