Mission control rooms rarely celebrate crash landings. But the collision of NASA’s DART spacecraft with an asteroid was a resounding success.
Around 7:15 p.m. EDT on September 26, the spacecraft swooped down on Dimorphos, a lunar asteroid orbiting a larger space rock named Didymos. The mission’s goal was to bring Dimorphos slightly closer to its parent asteroid, shortening its 12-hour orbit around Didymos by several minutes.
The Asteroid double redirect testor DART, is the world’s first attempt to alter the motion of an asteroid by driving a space probe into it (SN: 06/30/20). Neither Dimorphos nor Didymos pose a threat to Earth. But seeing how well the DART maneuver worked will reveal just how easy it is to alter an asteroid’s trajectory – a strategy that could protect the planet if a large asteroid were ever discovered on a collision course with Earth. .
“We don’t know of any large asteroids that would be considered a threat to Earth that would come anytime in the next century,” says DART team member Angela Stickle, a planetary scientist at the Applied Physics Laboratory at the Institute. Johns Hopkins University in Laurel, Md. “The reason we’re doing something like DART is because there are asteroids that we haven’t discovered yet.”
Astronomers have spotted nearly every mile-mile asteroid in the solar system that could end civilization if it hit Earth, says Jessica Sunshine, a planetary scientist at the University of Maryland at College Park who is also part of the DART team. . But when it comes to space rocks around 150 meters wide, like Dimorphos, “we only know where about 40% of them are,” says Sunshine. “And that’s something that, if it hit, would definitely wipe out a city.”
Dimorphos is a safe asteroid to give an experimental boost, says Mark Boslough, a physicist at Los Alamos National Laboratory in New Mexico who has studied planetary protection but is not involved in DART. “It’s not on a collision course” with Earth, he says, and DART “can’t hit it hard enough to put it on a collision course.” The DART spacecraft weighs only two vending machines, while Dimorphos is considered almost as heavy as the Great Pyramid of Giza in Egypt.
After a 10-month journey, DART encountered Didymos and Dimorphos near their closest approach to Earth, about 11 million kilometers away. Until the very end of its journey, DART could only see the largest asteroid, Didymos. But about an hour before impact, DART spotted Dimorphos in its line of sight. Using its onboard camera, the spacecraft headed for the asteroid moon and slammed into it at around 6.1 kilometers per second, or nearly 14,000 miles per hour.
Nasa
DART’s camera power went out after impact. But another probe nearby should have filmed the collision. The lightweight Italian CubeSat for asteroid imaging traveled to Dimorphos aboard DART but detached weeks before impact to watch the event from a safe distance. His mission was to fly past Dimorphos about three minutes after the DART impact to take pictures of the crash site and the resulting plume of asteroid debris launched into space. The probe should return images of the DART’s disappearance to Earth in a few days.
“I was absolutely thrilled, especially as we saw the camera get closer and realized all the science that we’re going to learn,” NASA deputy administrator Pam Melroy said after impact. “But the best part was seeing, at the end, that there was no doubt there would be an impact, and seeing the team delighted with their success.”
The DART impact should push Dimorphos into a closer and shorter orbit around Didymos. Telescopes on Earth can time the timing of this orbit by observing how the amount of light from the twin asteroid system changes as Dimorphos passes in front and behind Didymos.
“It really is a beautifully designed experience,” says Boslough. In the coming weeks, dozens of telescopes on every continent will be watching Dimorphos to see just how much DART has altered its orbit. The Hubble and James Webb Space Telescopes can also obtain images.
“It will be really interesting to see what comes out of it,” says Amy Mainzer, a planetary scientist at the University of Arizona in Tucson who is not involved in DART. “Asteroids have a way of surprising us,” she says, because it’s difficult to know the precise chemical composition and internal structure of a space rock based on Earth observations. Thus, the post-impact movement of Dimorphos may not exactly match researchers’ expectations.
The DART team will compare data on Dimorphos’ new orbit with their computer simulations to see how close those models were to predicting the asteroid’s actual behavior and adjust them accordingly. “If we can make our models replicate what actually happened, then you can use those models to [plan for] other scenarios that may arise in the future” – such as the discovery of a real killer asteroid, says Wendy Caldwell, DART team member, mathematician and planetary scientist at Los Alamos National Laboratory.
“No matter what happens,” she says, “we’ll get valuable information for the science community and the planetary defense community.”