What was the DART mission?
DART (Double Asteroid Redirection Test) was a NASA spacecraft that deliberately crashed into the small asteroid Dimorphos on 26 September 2022, shortening its orbit around a larger asteroid by about 32 minutes and proving that an asteroid can be nudged off course.
DART, short for Double Asteroid Redirection Test, was the world's first full-scale experiment in planetary defence. The question it set out to answer was simple: if we hit an asteroid hard enough with a spacecraft, will its path change in a measurable way?
The target was chosen with care. Didymos is an asteroid about 780 m across, and it has a small moon, Dimorphos, roughly 150 m wide, which circles it every 11 hours and 55 minutes. Neither posed any threat to Earth. Because Dimorphos orbits Didymos, any change in its speed would show up as a change in that orbital period, which astronomers could measure from Earth by watching how the pair's combined brightness rose and fell.
DART launched in November 2021. On 26 September 2022 it steered itself into Dimorphos at about 6.1 km/s, sending back pictures of a boulder-strewn surface until the final second. A small Italian satellite called LICIACube, released beforehand, photographed the huge plume of debris thrown out by the impact. Telescope measurements afterwards showed that the orbit had shortened by about 32 minutes, far more than the minimum of 73 seconds the team had hoped for. The ejected rubble acted like a rocket exhaust, giving Dimorphos an extra push beyond the impact itself.
The result showed that a "kinetic impactor" can work, especially against loosely bound rubble-pile asteroids, provided we have years of warning so that a small nudge can grow into a large miss. The European Space Agency's Hera spacecraft, launched in October 2024 and due to reach the pair in late 2026, will survey the crater and measure the mass of Dimorphos, turning DART's single experiment into a properly calibrated tool.