A European spacecraft has begun close inspections of an asteroid rammed by NASA four years ago in a planetary defence test. The European Space Agency announced Wednesday that its Hera spacecraft is now studying Didymos and its moonlet Dimorphos from just 25 to 30 kilometres away.

NASA's DART spacecraft, short for Double Asteroid Redirection Test, deliberately slammed into the small Dimorphos in 2022 to see whether such a move might one day help save Earth from a killer space rock. The impact shortened the moonlet's orbit around Didymos and, more importantly, nudged it onto a slightly different path around the sun. The impact also sent rubble and even boulders flying off Dimorphos, providing an extra kick to its momentum, and the debris trail stretched more than 10,000 kilometres into space for months. Some of that debris could still be in the vicinity, according to scientists.S1S2

Hera, a car-sized spacecraft launched in 2024, is carrying 25 science instruments as well as a pair of shoebox-sized CubeSats to survey Dimorphos more closely and attempt to land on it. Next month it will venture even closer, to about 20 kilometres away. ESA officials describe this phase as a "crash site investigation" worthy of its finest robotic detective. Dimorphos is an estimated 151 metres in diameter, while Didymos is roughly 780 metres across.S1S2