NASA’s DART spacecraft changed 2 asteroids’ orbit around the sun

For the first time, humankind has changed a space rock’s orbit around the sun.

Four years ago, NASA rammed its DART spacecraft into the asteroid Dimorphos. The goal was to see if a space probe could change an asteroid’s motion. Why? It could be useful if a big rock were ever headed for Earth.

Soon after the crash, it was clear that DART had knocked its asteroid closer to Didymos, an even bigger rock that it orbits. Now, NASA reports that the smashup had an even bigger impact. It changed the asteroid duo’s speed as they orbit the sun together.

Scientists Say: Asteroid, meteor and meteorite

DART’s crash landing slowed the asteroid pair by 10 micrometers per second. That might not sound like much. But tweaking the motions of space rocks millions of kilometers (miles) from Earth is a huge deal. It could inform plans for shielding our planet from future asteroid strikes.

Researchers shared the findings March 6 in Science Advances.

DART is short for Double Asteroid Redirection Test. The initial goal had been to simply nudge Dimorphos into a tighter orbit around Didymos. Mission leaders aimed to cut 73 seconds off Dimorphos’ nearly 12-hour path around its partner. In reality, the crash shortened Dimorphos’ orbit around Didymos by 32 minutes.

Most of that change came from the impact itself. Like giving the asteroid a big shove, the spacecraft pushed Dimorphos closer to Didymos. The crash also blasted rocks off Dimorphos’ surface. The motion of that flying debris gave the asteroid an extra kick.

But some of the debris knocked off Dimorphos didn’t just leave that space rock. It escaped the gravity of the two-asteroid system altogether. That escaping debris took some momentum away from the duo. As a result, their joint motion around the sun changed, reports Rahil Makadia. He studies planetary defense at the University of Illinois in Urbana–Champaign.

Clues in tiny eclipses

To figure out how much the asteroids’ motion changed, astronomers watched the rocks pass in front of distant stars. As the asteroids passed by, they dimmed some of the stars’ light — like tiny eclipses. These blinks can be seen only from specific locations, which can fall anywhere on Earth.  

Astronomers could predict when Dimorphos and Didymos should pass in front of stars, based on their old path around the sun. By comparing those predictions to observations, they could see how much the asteroids’ path changed after DART’s hit.

Asteroids: Avoiding an Earthly smashup

Between October 2022 and March 2025, Makadia and the team gathered 22 such measurements. Amateur astronomers provided a lot of these data, Makadia says. “There was an observer who drove two days each way into the Australian outback to get these measurements.”

The asteroids’ orbit around the sun was about 150 milliseconds longer than before the DART impact, the new data show.

The European Space Agency’s Hera spacecraft will reach Didymos and Dimorphos later this year. When it does, the spacecraft could confirm the asteroids’ new orbit.

Didymos and Dimorphos were not a threat to Earth before DART. They aren’t now, either. But knowing how an impact changes one asteroid’s orbit can help figure out how to defend Earth from a dangerously big incoming space rock. That’s crucial, Makadia says, “in case we need to [deflect an asteroid] for real.”