DART is NASA’s first “planetary defense” mission. The goal was to test whether this technique, called a kinetic impactor, would deliver enough of a punch to a speeding space rock to knock it significantly off course.

NASA crashes spacecraft into asteroid, passing planetary defense test

It did. Before DART’s arrival, Dimorphos orbited Didymos in 11 hours and 55 minutes. Then: Blam! The newly calculated orbit: 11 hours and 23 minutes.

That 32-minute change in the orbital period was at the high end of a range of estimated outcomes, NASA’s head of planetary science, Lori Glaze, said. DART surpassed the agency’s minimum benchmark for a successful mission by more than 25 times.

“We showed the world NASA is serious as a defender of this planet,” said NASA Administrator Bill Nelson.

The mission “felt like a movie plot,” he said. “But this was not Hollywood.”

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Despite the enthusiasm emanating from NASA officials, there is not a fully developed system for intercepting asteroids. The key to planetary defense is finding potentially hazardous asteroids long before they cross Earth’s path. Astronomers can calculate whether they are on a trajectory to strike the planet.

“You gotta know they’re coming,” Glaze said.

The idea of a kinetic impactor is to give a hazardous asteroid a nudge many years before its anticipated impact with Earth. This is not a last-minute technique for saving the world.

“We really need to have that warning time for a technique like this to be effective,” said Nancy Chabot, DART coordination lead at the Johns Hopkins University Applied Physics Laboratory, which handled the mission under a NASA contract.

Big asteroids that might menace Earth are easily spotted, and their orbits calculated many decades into the future. But many smaller asteroids in the general size range of Dimorphos, which is about 160 meters in diameter, are harder to detect.

Asteroids are not identical. Some are hard, solid bodies, while others are “rubble piles.” The composition and shape of Dimorphos were not known prior to the arrival of DART. Only in the last few minutes of the mission did the asteroid come into focus. The impact created a stunning plume of ejecta, and the dramatic motion of the asteroid came in part from the way it recoiled as boulders and fine particles spewed into space.

The mission was already in the books as an engineering triumph simply by virtue of a successful collision — indeed a bull's eye — dramatically captured by the spacecraft’s camera in the final moments before impact.

The laws of physics dictated that there had to be some effect. And images captured by a trailing cubesat, provided by the Italian Space Agency and deployed by DART 15 days before impact, showed material hurtling into space. Subsequent observations from telescopes on Earth as well as the Hubble and Webb space telescopes revealed a long trail of debris, creating a comet-like effect.

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Not until Tuesday, after much analysis, did NASA reveal the precise change in Dimorphos’s orbit. The analysis is continuing, and one question is whether the rock has gone wobbly.

“We should not be too eager to say one test on one asteroid tells us how every other asteroid would behave,” NASA program scientist Thomas Statler cautioned.

Even so, the bottom line is that the DART mission worked just like scientists and engineers had hoped.

“Let’s all just kind of take a moment to soak this in,” Glaze said. “For the first time ever, humanity has changed the orbit of a planetary body.”