USA · NASA/APLfirstrobotic
September 26, 2022
DART impacts Dimorphos — first asteroid deflection test
In the mission operations center at the Johns Hopkins Applied Physics Laboratory on the evening of 26 September 2022, the last pictures arrived one per second. A grey smudge became a lumpy world, then a boulder field rushing up to fill the frame, and then, at 7:14 p.m. Eastern time, the final image cut off mid-transmission as the spacecraft struck home. The room erupted. For the first time in history, the death of a spacecraft was the proof of its success: DART had flown itself into an asteroid at full speed, exactly as designed.
The target was Dimorphos, a 160-metre moonlet circling the larger asteroid Didymos some 11 million kilometres from Earth, a natural laboratory chosen because the pair posed no threat whatsoever. The 570-kilogram spacecraft closed at roughly 22,500 kilometres per hour, steering itself through the final four hours with its SMART Nav autonomous targeting system, since radio commands from Earth would arrive far too slowly for terminal guidance. Dimorphos had never been resolved by any telescope; DART discovered its target's true face less than an hour before destroying itself against it.
Two weeks later, on 11 October, NASA confirmed the result. Dimorphos's orbit around Didymos had shortened by 32 minutes, against a pre-launch success threshold of just 73 seconds, a margin of more than 25 times. Later analysis refined the change to about 33 minutes and found the impact had even reshaped the moonlet. Most of the push came not from the spacecraft itself but from the recoil of over a thousand tonnes of rock blasted into space, a plume so vast that telescopes tracked a 10,000-kilometre tail streaming off the asteroid for months.
Trailing three minutes behind, an Italian CubeSat called LICIACube swept past to photograph the eruption of debris, Italy's first deep-space mission serving as the world's smallest action photographer. The follow-up belongs to Europe: ESA's Hera spacecraft launched in October 2024 and is en route to survey the crater and measure Dimorphos's new shape in detail. Together the missions close the loop on a question humanity had only ever answered in the movies: yes, we can move an asteroid.
“All of us have a responsibility to protect our home planet. After all, it's the only one we have.”
Mission Data
Launch
24 Nov 2021 (Falcon 9, Vandenberg)
Impact
26 Sep 2022, 23:14 UTC
Impact speed
~22,500 km/h
Spacecraft mass at impact
~570 kg
Orbit period change
32 min (refined to ~33 min)
Distance from Earth
~11 million km
Key Facts
NASA's bar for success was shifting Dimorphos's orbit by 73 seconds; DART shifted it by over half an hour, beating the threshold more than 25 times over.
The spacecraft did its own targeting: for the final four hours, the SMART Nav autonomy system steered toward an asteroid that no telescope on Earth had ever resolved.
Recoil from more than a million kilograms of ejected rock gave Dimorphos a bigger shove than the spacecraft impact itself.
Italy's LICIACube, a briefcase-sized CubeSat released 15 days before impact, flew past three minutes afterwards to photograph the debris plume on Italy's first deep-space mission.
The impact did not just move Dimorphos, it deformed it; NASA's 2024 analysis found the moonlet's shape changed from a squashed sphere toward a stretched 'watermelon'.
Why It Mattered
DART transformed planetary defence from a thought experiment into an engineering discipline with flight heritage. For the first time, humanity deliberately and measurably changed the orbit of a celestial body, validating the kinetic impactor as a practical tool should a dangerous asteroid ever be found on a collision course. Its data on momentum transfer, including the discovery that ejecta recoil multiplies the push, now anchors every serious deflection model, and the mission seeded an international pipeline with ESA's Hera flying out to inspect the aftermath.
