NASA’s space rock-smashing mission successfully changed the orbit of an asteroid, the agency announced Tuesday.
The Double Asteroid Redirection Test (DART) spacecraft slammed into an asteroid called Dimorphos on September 26, pushing it slightly closer to its giant parent asteroid, Didymos.
The mission was a practice run for deflecting a dangerous asteroid away from Earth. As far as NASA knows, no such space rock is currently on a collision course with Earth, at least for the next 100 years. But experts warn it’s only a matter of time.
“We showed the world that NASA is serious as a defender of this planet,” Bill Nelson, NASA’s administrator, said in a briefing on Tuesday. “This is a watershed moment for planetary defense and all of humanity.”
Nelson said it would have been a “huge success” to push Didymos just enough to shorten its orbit by 10 minutes. The minimum orbit change required for DART to be successful was 73 seconds.
However, observations by astronomers with Earth-based telescopes revealed that Dimorphos now orbits Didymos 32 minutes faster than it did before the DART impact — give or take two minutes.
Previously, it took 11 hours and 55 minutes for Dimorphos to circle Didymos. Now, with a nudge from DART, it only takes 11 hours and 23 minutes.
“For the first time ever, humanity has changed the orbit of a planetary body,” Lori Glaze, director of NASA’s Planetary Science Division, said in the briefing.
Part of Dimorphos’s movement came from the sheer kinetic force of the golf cart-sized probe smashing into it. But follow-up observations reveal that some of the movement was caused by recoil from the stream of debris that launched off the asteroid and into space.
Like a jet of air streaming from a balloon pushes the balloon in the opposite direction, this jet of “ejecta” pushed Dimorphos away from the crash site and toward Didymos.
Astronomers are still observing the asteroid system, collecting and analyzing more data, to understand how much the ejecta affected the orbit change.