DART
DART was a NASA spacecraft that crashed into the asteroid moon Dimorphos in 2022 to test deflecting an asteroid.
DART, the Double Asteroid Redirection Test, was the first mission to test planetary defence by changing an asteroid's motion. Launched in November 2021, the 570-kilogram craft struck Dimorphos, a moonlet about 160 metres across orbiting the larger asteroid Didymos, on 26 September 2022 at about 6.1 kilometres per second.
Neither asteroid posed any danger to Earth; the pair was chosen because a change in Dimorphos's orbit around Didymos could be measured from Earth. Before the impact, Dimorphos took 11 hours 55 minutes to orbit. Afterwards, the period was about 32 minutes shorter, far more than the minimum goal of 73 seconds.
The extra change came from the huge plume of debris thrown off, which acted like a rocket exhaust. An Italian cubesat, LICIACube, photographed the plume. The result showed that a kinetic impactor could push a hazardous asteroid off course if it were found early enough.
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