NASA’s DART mission was the first to demonstrate a planetary-defense asteroid impact.
The Double Asteroid Redirection Test launched on November 24, 2021, and struck Dimorphos, the small moonlet of the asteroid Didymos, on September 26, 2022. DART was designed to test whether a spacecraft could intentionally alter an asteroid’s motion through a kinetic impact.
The impact shortened Dimorphos’s orbital period by about 32 minutes, far exceeding the mission’s minimum success criterion. DART did not destroy the asteroid, and it was not intended to stop a known threat. Deep Impact also deliberately struck a small body, Comet Tempel 1, but its goal was scientific study rather than planetary defense. The European Space Agency’s Hera mission is examining the DART impact site in greater detail.