Studying this asteroid could help protect Earth from future asteroid strikes
A spaceship slowed down orbit of a pair of asteroids around the sun of more than 10 micrometers per second – this is the first time that human activity has modified the orbit of a celestial object, researchers report March 6 in Scientific advances. The experiment could have implications for protecting Earth from future asteroid strikes.
NASA’s Double Asteroid Redirection Test, or DART, intentionally crashed a spaceship in the smaller asteroid Dimorphos in 2022. The goal was to change Dimorphos’ orbit around its larger sibling, Didymos. In one month, researchers showed that the impact shortened Dimorphos’ 12-hour orbit by 32 minutes.
Most of this change came from the impact itself. Some of it came from flying impact debris, which gave Dimorphos a small kick in the opposite direction of his movement.
Some of the the overturned rocks of Dimorphos have completely fled the surrounding areaescaping the gravitational influence of the Dimorphos-Didymos pair, explains planetary defense researcher Rahil Makadia of the University of Illinois Urbana-Champaign. These rocky escapes took some momentum from the duo and modified their common movement around the sun.
To determine how much this motion was affected, astronomers watched as asteroids passed in front of distant stars, dimming the light of some stars like a small eclipse. These blinks, called stellar occultations, can be visible from anywhere on Earth and are predictable in advance.
“Often, they are amateur astronomers who go to the middle of nowhere to follow Didymos based on forecasts,” Makadia explains. “There was an observer who drove two days each way into the Australian outback to get these measurements.”
Makadia and his colleagues collected 22 such measurements taken between October 2022 and March 2025. Calculating the distance between occultation times and predictions revealed that the asteroids’ orbit around the sun was about 150 milliseconds slower than before the DART impact.
The result could be confirmed later this year, when the European Space Agency Hera spaceship arrives at Didymos and Dimorphos for follow-up observations.
Didymos and Dimorphos are not a threat to Earth, Makadia says, and were not before DART. But knowing how a deliberate impact changes the orbit of one asteroid can help develop defense plans against another, “in case we need to do a kinetic impact for real.”
