THE DOUBLE ASTEROID REDIRECTION TEST (DART): THE FIRST PLANETARY DEFENSE TEST MISSION (Invited Presentation)

On 26 September 2022, NASA’s Double Asteroid Redirection Test (DART) mission demonstrated technology that could one day potentially prevent an asteroid impact. The technology, called kinetic impact, changes the path of an asteroid through space by intentionally slamming a spacecraft into it. The DART mission targeted the 150-m diameter asteroid Dimorphos, which is the moon of the larger 760-m diameter asteroid called Didymos. This test was done at a binary asteroid system in the fall of 2022 so that the asteroids were close enough to Earth that telescopes on the ground could quantity the change in Dimorphos’ orbit.

During the mission’s final four hours, the DART spacecraft autonomously navigated to impact and slammed into Dimorphos amid three large boulders named Atabaque, Bodhran, and Caccavella. The impact occurred within 25 meters of the asteroid’s center of figure, which was close to ideal for deflection. Images taken by the spacecraft during the four hours leading to impact were streamed to the ground every second, which allowed people around the world to watch as Didymos and Dimorphos changed from points of light to resolved geological worlds.

The impact of the DART spacecraft decreased Dimorphos’ orbital period by 33 minutes and excavated a wide cone of material. The ejecta plume was observed by the LICIACube CubeSat contributed by the Italian Space Agency, as well as by telescopes on the ground and in space. Over time, the ejecta plume reshaped into an extended tail, which remains observable as of early July 2023.

Numerical simulations indicate that ejecta excavated by the DART impact substantially enhanced the asteroid deflection. Depending on the mass of Dimorphos—which is poorly constrained—the ejecta contributed 2 to 5 times more momentum to the deflection than the DART spacecraft itself. This encouraging result means that kinetic impact could be used to deflect larger asteroids (for a given warning time) or with shorter warning time (for a given asteroid size).

Although we know of no asteroids that pose a threat to Earth for at least the next century, the catalog of the near-Earth asteroid population is incomplete for objects large enough to cause regional devastation. The success of the DART mission builds optimism about our ability to defend Earth against an asteroid threat, should one be discovered with adequate warning time.