Direct detection of an asteroid’s heliocentric deflection: The Didymos system after DART
- Rahil Makadia
- Steven R. Chesley
- David Herald
- Davide Farnocchia
- Nancy L. Chabot
- Shantanu P. Naidu
- Andrew S. Rivkin
- Alexandros Siakas
- Damya Souami
- Paolo Tanga
- Sotirios Tsavdaridis
- Kleomenis Tsiganis
- Sébastien Bouquillon
- Siegfried Eggl
2026-03-06
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.