DART

DART, NASA's Double Asteroid Redirection Test, was the first mission dedicated to demonstrating a way to deflect an asteroid, by changing its motion in space with a kinetic impact.^[1] It was built and operated by the Johns Hopkins Applied Physics Laboratory for NASA's Planetary Defense Coordination Office.^[2]

The mission

DART launched on a SpaceX Falcon 9 rocket from Vandenberg Space Force Base in California on 24 November 2021.^[3] Its target was Dimorphos, a moonlet about 170 m across that orbits the larger asteroid Didymos; neither posed any threat to Earth.^[3] Fifteen days before impact, DART released LICIACube, a small spacecraft from the Italian Space Agency, to photograph the collision.^[3] DART struck Dimorphos on 26 September 2022 at about 6.1 km per second, some 11 million km from Earth.^[3]

What it found

Before the impact, Dimorphos took 11 hours and 55 minutes to circle Didymos, and NASA had set a change of 73 seconds as the minimum for success.^[4] The orbit was shortened by 33 minutes, plus or minus 1 minute.^[5] It was the first time humans had deliberately changed the motion of a celestial object.^[4]

Debris thrown off by the impact pushed Dimorphos further, so the momentum change was larger than the spacecraft alone could have given.^[6] The impact also shifted the pair's orbit around the Sun by a fraction of a second.^[2] The team concluded that a kinetic impactor can change an asteroid's path, given warning time of several years at a minimum and preferably decades.^[6]

ESA's Hera mission followed to survey the aftermath of the impact.^[7] The test in the context of other defense work is covered in Planetary defense, and the target pair in Didymos and Dimorphos.