In September, a small NASA spacecraft beamed images of the asteroid Dimorphos back to Earth. With each passing second, the asteroid appeared closer and closer. When the craft stopped transmitting, NASA scientists cheered—they knew immediately that their spacecraft had managed to hit the asteroid, which was their goal all along. But at the time, NASA didn’t yet know if they’d achieved another goal of the mission: altering the asteroid’s trajectory.
On Tuesday, NASA officials announced that their mission was a resounding success. As a result of the crash they’d engineered, Dimorphos’s orbit around the asteroid Didymos had been shortened by 32 minutes, from 11 hours and 55 minutes to 11 hours and 23 minutes. The agency had previously set a minimum benchmark for success at 73 seconds.
“This is a watershed moment for planetary defense and all of humanity,” NASA Administrator Bill Nelson said during a Tuesday news briefing. “We conducted humanity’s first planetary defense test, and we showed the world that NASA is serious as a defender of this planet.”
NASA launched the Double Asteroid Redirection Test (DART) spacecraft in November 2021 atop a SpaceX Falcon 9 rocket. After traveling about seven million miles in ten months, DART rammed into Dimorphos on September 26. While the asteroid poses no threat to Earth, scientists wanted to test their defense abilities in case of a future incoming space rock.
As expected, the images indicated that Dimorphos is what’s called a rubble-pile asteroid, meaning it’s a pile of rocks held together by gravity rather than a singular, solid structure. DART’s impact with the asteroid caused it to eject “many tons” of rock into space, which also aided in knocking it off its course—similar to how “a jet of air streaming out of a balloon sends the balloon in the opposite direction,” per NASA.
This just in: The #DARTmission impact is confirmed to have changed the orbit of moonlet Dimorphos around its asteroid Didymos.— NASA (@NASA) October 11, 2022
For the first time ever, humans changed the motion of a celestial object. More details: https://t.co/aQj8N7fnuV pic.twitter.com/NLR6AqEcaO
“I don’t think most folks expected them to blast it to hell as much as they did,” John O’Meara, chief scientist at the Keck Observatory, where astronomers observed the debris stream caused by the impact, tells National Geographic’s Nadia Drake. “I guess when you beat up a rubble pile, it de-piles.”
DART program scientist Tom Statler said in the briefing that researchers will continue analyzing data from the mission to calculate the mass of Dimorphos as well as the sizes of the particles from the ejecta plume, their mass, the direction in which they traveled and how fast they moved. Additionally, they’ll work to understand in-depth the properties of Dimorphos’s new orbit. In 2027, a European spacecraft will arrive at the Didymos system to conduct up-close research on the asteroid and its moon.
“It’s exciting that we’ve taken this first step to develop and now to successfully demonstrate asteroid deflection,” Nancy Chabot, DART coordination lead at the Johns Hopkins Applied Physics Laboratory, said in the briefing. Even so, she said, “there’s still a lot of work to do.”
While Dimorphos will provide scientists with ample data, not all asteroids are the same—for example, a solid rock may react differently to a spacecraft impact than a pile of rubble does.
“We should not be too eager to say one test on one asteroid tells us exactly how every other asteroid would behave in a similar situation,” Statler said in the briefing. “But what we can do is use this test as an anchor point for our physics calculations and our simulations that tell us how different kinds of impacts in different situations should behave.”