The Double Asteroid Redirection Test (DART) was a NASA space mission to test a method of planetary defense against near-Earth objects (NEOs). It was designed to assess how much a spacecraft impact can deflect an asteroid by hitting it head-on. The target asteroid, Dimorphos, is a 525 feet (160 m) wide moonlet of the asteroid Didymos; neither asteroid poses an impact threat to Earth, but their joint characteristics made them an ideal target. Launched on 24 November 2021, the DART spacecraft collided with Dimorphos at 14,000 mph (23,000 km/h) on 26 September 2022 about 6.8 million miles (10.9 million kilometers) from Earth. The collision shortened Dimorphos's orbit around Didymos by 32 minutes, greatly in excess of the pre-defined success threshold of 73 seconds.

Wikipedia: https://en.wikipedia.org/wiki/Double_Asteroid_Redirection_Test. Related NASA reference: https://science.nasa.gov/mission/dart/. Description adapted from Wikipedia contributors (CC BY-SA 4.0; https://creativecommons.org/licenses/by-sa/4.0/).