DART: the day humanity moved an asteroid
How a 610 kg spacecraft hit Dimorphos at 6 km/s, shortened its orbit by 33 minutes and proved kinetic-impact deflection works.
Published 2026-10-23
On September 26, 2022, a NASA spacecraft the size of a small car flew straight into a small asteroid moon on purpose. It was the world's first full-scale test of a planetary-defense technique.[1][6]
The target
DART's target was Dimorphos, the roughly 170-meter moon of Didymos.[1] Neither body is a danger to Earth.[6] Because Dimorphos orbits Didymos, astronomers could measure any change in its orbit precisely by timing the dips in brightness as the two asteroids pass in front of each other.
The spacecraft
DART was a 610 kg impactor that carried no science instruments, only navigation sensors. It cost about US$330 million.[6] Its camera, DRACO, fed images to SMART Nav, autonomous guidance software that steered the spacecraft to the center of Dimorphos in the final hours without human help.[6] DART was a joint project of NASA and the Johns Hopkins University Applied Physics Laboratory.[6]
Launch and impact
DART launched on a SpaceX Falcon 9 from Vandenberg Space Force Base in California on November 24, 2021.[1] Ten months later it struck Dimorphos at about 6.1 km/s while the asteroid was about 11 million km from Earth. Its last complete image was taken from about 12 km away, two seconds before impact.[1]
The result
Dimorphos had taken about 12 hours to circle Didymos. Telescope observations showed the impact shortened that by 33 minutes; NASA had set a success threshold of just 73 seconds.[1]
The ejecta mattered as much as the spacecraft. The momentum transferred was about 3.6 times what DART alone delivered, because the debris blasted off Dimorphos acted like extra thrust.[6] Over 1,000,000 kg of dusty ejecta was thrown into space, forming a tail at least 30,000 km long.[6]
A nudge around the Sun too
A study published in March 2026 found that the impact also changed the Didymos pair's roughly 770-day orbit around the Sun by a fraction of a second — tiny, but measurable.[1] Scientists describe this as the first time human action measurably changed a celestial body's orbit around the Sun.[6]
Numbered citations link to the sources list on the Didymos overview page.