NASA has confirmed the spacecraft it smashed into an asteroid last month succeeded in nudging it from its natural orbit.
It marks the first time humanity has altered the motion of a natural body in space.
The DART mission (Double Asteroid Redirection Test) is also the first test of a planetary defence system designed to prevent a potential doomsday meteorite collision with Earth.
The $325 million (€333 million) mission passed a critical milestone late last month after it crashed into a 160-metre asteroid named Dimorphos, which is a moonlet of an asteroid five times larger called Didymos.
The pair had been orbiting the sun for aeons without threatening Earth before the DART spacecraft hit its target 11.3 million km from our planet following a 10-month journey through space.
Findings of telescope observations unveiled at a NASA news briefing in Washington confirmed the test flight of the DART spacecraft achieved its primary objective: changing the direction of an asteroid through sheer kinetic force.
Astronomical measurements over the past two weeks showed the target asteroid was bumped slightly closer to the larger parent asteroid it orbits and that its orbital period was shortened by 32 minutes, NASA scientists said.
"This is a watershed moment for planetary defence and a watershed moment for humanity," NASA chief Bill Nelson told reporters in announcing the results. "It felt like a movie plot, but this was not Hollywood."
Last month's impact was monitored in real-time from the mission operations centre at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, where the spacecraft was designed and built for NASA.
Comparison of pre and post-impact measurements of the Dimorphos-Didymos pair as one eclipses the other shows the orbital period was shortened to 11 hours, 23 minutes, with the smaller object bumped tens of metres closer to its parent.
Tom Statler, DART program scientist for NASA, said the collision also left Dimorphos "wobbling a bit," but additional observations would be necessary to confirm that.
The outcome "demonstrated we are capable of deflecting a potentially hazardous asteroid of this size," if it were discovered well enough in advance, said Lori Glaze, director of NASA's planetary science division. "The key is early detection".
Nancy Chabot, DART's coordination lead at APL, said Dimorphos "is a size of asteroid that is a priority for planetary defence".
A Dimorphos-sized asteroid, while not capable of posing a planet-wide threat, could level a major city with a direct hit.
Scientists had predicted the DART impact would shorten Dimorphos' orbital path by at least 10 minutes but would have considered a change as small as 73 seconds a success.
So the actual change of more than a half hour, with a margin of uncertainty plus or minus two minutes, exceeded expectations.
The relatively loose composition of rubble that Dimorphos appears to consist of may be a factor in how much the asteroid was budged by DART's blow.
The impact blasted tonnes of rocky material from the asteroid's surface into space, visible in telescope images as a large debris plume, producing a recoil effect that added to the force exerted on Dimorphos from the collision itself, NASA said.
Launched by a SpaceX rocket in November 2021, DART made most of its voyage under the guidance of flight directors on the ground, with control handed over to the craft's autonomous onboard navigation system in the final hours of the journey.
Dimorphos and Didymos are both tiny compared with the cataclysmic Chicxulub asteroid that struck Earth some 66 million years ago, wiping out about three-quarters of the world's plant and animal species including the dinosaurs.
Smaller asteroids are far more common and present a greater theoretical concern in the near term, making the Didymos pair suitable test subjects for their size, according to NASA scientists and planetary defence experts.