Elliptical ejecta of asteroid Dimorphos is due to its surface curvature.

Kinetic deflection is a planetary defense technique delivering spacecraft momentum to a small body to deviate its course from Earth. The deflection efficiency depends on the impactor and target. Among them, the contribution of global curvature was poorly understood.

Morphology of ejecta features from the impact on asteroid Dimorphos.

Hypervelocity impacts play a significant role in the evolution of asteroids, causing material to be ejected and partially reaccreted. However, the dynamics and evolution of ejected material in a binary asteroid system have never been observed directly. Observations of Double Asteroid Redirection Test (DART) impact on asteroid Dimorphos have revealed features on a scale of thousands of kilometers, including curved ejecta streams and a tail bifurcation originating from the Didymos system.

The geology and evolution of the Near-Earth binary asteroid system (65803) Didymos.

Images collected during NASA's Double Asteroid Redirection Test (DART) mission provide the first resolved views of the Didymos binary asteroid system. These images reveal that the primary asteroid, Didymos, is flattened and has plausible undulations along its equatorial perimeter. At high elevations, its surface is rough and contains large boulders and craters; at low elevations its surface is smooth and possesses fewer large boulders and craters.

Recent collisional history of (65803) Didymos.

The Double Asteroid Redirection Test (DART, NASA) spacecraft revealed that the primary of the (65803) Didymos near-Earth asteroid (NEA) binary system is not exactly the expected spinning top shape observed for other km-size asteroids. Ground based radar observations predicted that such shape was compatible with the uncertainty along the direction of the asteroid spin axis. Indeed, Didymos shows crater and landslide features, and evidence for boulder motion at low equatorial latitudes.

Momentum transfer from the DART mission kinetic impact on asteroid Dimorphos.

The NASA Double Asteroid Redirection Test (DART) mission performed a kinetic impact on asteroid Dimorphos, the satellite of the binary asteroid (65803) Didymos, at 23:14 UTC on 26 September 2022 as a planetary defence test. DART was the first hypervelocity impact experiment on an asteroid at size and velocity scales relevant to planetary defence, intended to validate kinetic impact as a means of asteroid deflection. Here we report a determination of the momentum transferred to an asteroid by kinetic impact.

Ejecta from the DART-produced active asteroid Dimorphos.

Some active asteroids have been proposed to be formed as a result of impact events. Because active asteroids are generally discovered by chance only after their tails have fully formed, the process of how impact ejecta evolve into a tail has, to our knowledge, not been directly observed. The Double Asteroid Redirection Test (DART) mission of NASA, in addition to having successfully changed the orbital period of Dimorphos, demonstrated the activation process of an asteroid resulting from an impact under precisely known conditions.

Successful kinetic impact into an asteroid for planetary defence.

Although no known asteroid poses a threat to Earth for at least the next century, the catalogue of near-Earth asteroids is incomplete for objects whose impacts would produce regional devastation. Several approaches have been proposed to potentially prevent an asteroid impact with Earth by deflecting or disrupting an asteroid. A test of kinetic impact technology was identified as the highest-priority space mission related to asteroid mitigation.