NASA's DART (2023): The First Test of Deflecting an Asteroid

NASA’s DART spacecraft crashed into the small asteroid Dimorphos on 26 September 2022, the first full-scale test of deflecting an asteroid. In a 2023 Nature paper, Terik Daly and colleagues reconstructed the impact from DART’s final images, and a companion study showed the asteroid’s orbit had measurably changed.

Why test asteroid deflection?

No known asteroid poses a threat to Earth for at least the next century. But the catalog of near-Earth asteroids is still incomplete for objects big enough to devastate a region if they hit. The Alvarez team’s 1980 evidence that an asteroid ended the age of dinosaurs made the stakes clear. Several ways to push a dangerous asteroid aside had been proposed, and a test of the simplest, the kinetic impactor, which means hitting the asteroid hard with a spacecraft, was ranked the top-priority mission for asteroid mitigation. Earlier missions had smashed into small bodies to study them, but none had tried to move one, and none had produced a measurable deflection.

What the paper found

• A direct hit. DART autonomously struck Dimorphos, the small moon of the near-Earth asteroid (65803) Didymos, on 26 September 2022.
• The exact spot. The spacecraft hit between two large boulders, grazing one of them.
• The full story of the last moments. The team reconstructed the timeline of the impact, the nature of the impact site, and the size and shape of Dimorphos.
• A big orbital change. A companion paper measured that the impact shortened Dimorphos’s 11.9-hour orbit around Didymos by 33.0 ± 1.0 minutes. Momentum from the spacecraft alone should have changed it by only about 7 minutes. The rest came from recoil: debris blasted off the surface pushed the asteroid like a rocket exhaust.

How they did it

The target was chosen with measurement in mind. Because Dimorphos orbits Didymos, telescopes on Earth can time that orbit by watching the pair’s combined light dip as one body passes in front of the other. Change the orbit, and the timing changes. That made the deflection measurable from the ground with light curves and radar.

DART steered itself to the target and sent back images until the moment of impact. Daly and colleagues used those final frames to map the impact site, locate where the spacecraft struck relative to the boulders, and model the shape of Dimorphos.

Why it mattered

DART proved that humanity can measurably change an asteroid’s orbit. The lesson of the dinosaur-killing impact became an engineering capability. The large boost from ejected debris also matters for planning: hitting an asteroid can deliver much more push than the spacecraft’s own momentum.

Defense starts with finding threats early. The Vera C. Rubin Observatory found 33 previously unknown near-Earth objects among more than 11,000 new asteroids in its early test surveys, before its 10-year survey began in mid-2026.

What we know now

ESA’s Hera mission, launched on 7 October 2024, is following up. It released its first images of Didymos in October 2026 and is due to rendezvous with the pair in November 2026 to survey the aftermath in detail (as of October 2026). Small bodies keep surprising us, from impact targets like Dimorphos to visitors like the interstellar object ‘Oumuamua. Planetary defense is now part of Solar System science.

Who wrote it

R. Terik Daly led the paper with Carolyn M. Ernst, Olivier S. Barnouin and the DART team. It was published on 1 March 2023 alongside a companion paper that measured the orbit change. Semantic Scholar lists about 187 citations (October 2026).

Read the original

Daly, R. T., Ernst, C. M., Barnouin, O. S., et al. (2023). “Successful kinetic impact into an asteroid for planetary defence.” Nature 616, 443-447. doi:10.1038/s41586-023-05810-5

Free to read: arXiv preprint.