Mission control rooms rarely celebrate a crash in ports. But the collision of NASA’s space shuttle with an asteroid was a mighty success.
At approximately 7:15 p.m. EDT on September 26, the ship crashed into Dimorphos, a large rock orbiting the moon’s asteroid called Didymos. The goal of the mission was to bring Dimorphos slightly closer to the hump of its parent asteroid, shortening its 12-hour orbit around Didymus by several minutes.
The Double Asteroid Redirection Test, or DART, was the world’s first attempt to change the motion of an asteroid by beaming it into space (SN: 6/30/20). Neither Dimorphos nor Didymos threatens Earth. But seeing how well the DART system works will reveal how easy it is to tamper with an asteroid’s trajectory – a strategy that could protect the planet if a large asteroid is caught in a collision course with Earth.
“We don’t know of any large asteroids that are going to be a threat to Earth anytime in the next century,” says DART team member Angela Stickle, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. “The reason we think it’s like a rocket is because there are asteroids that we haven’t found yet.”
Astronomers have spotted nearly every kilometer-wide asteroid in the solar system that could end civilization if it hit Earth, says Jessica Sunshine, a planetary scientist at the University of Maryland in College Park who was also on the launch team. But when the rock spaces are about 150 meters wide, like Dimorphos, “we only know where about 40 percent of them are,” Sol says. “And this is because, if he strikes, he will certainly send the city.”
Dimorphic asteroids are safe enough to provide experimental nakedness, says Mark Boslough, a scientist 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 VERTU “isn’t hard enough to put on a collision course.” DIRATA weighs as much as two vending machines, while Dimorphos is thought to be almost as hefty as the Great Pyramid of Giza in Egypt.
After a 10-month cruise, DART met Didymos and Dimorphos on their closest approach to Earth, about 11 million kilometers away. Towards the end of the road, Stipe could only see the larger asteroids, Didymos. But about an hour before the impact, Dimorphos spotted a warty Dimorphos in his field. Using its camera, the spacecraft attached itself to the asteroid’s moon and pushed toward it at about 6.1 kilometers per second, or about 14,000 miles per hour.
The DART camera feed went dark after the impact. But the second probe is expected to be nearby as the collision was caught on camera. The Italian Light CubeSat for Asteroid Imaging was flown to the Dimorphos spacecraft but detached two weeks before impact to observe the event from a safe distance. Its mission flew past Dimorphos about three minutes after the DART impact to snap images of the crash site and the asteroid debris plume launched into space. The probe is expected to return to Earth within a couple of days by releasing the transposed radiation images.
“I was absolutely thrilled, especially when we saw the camera coming up close and just seeing all the science we’re learning,” said Pam Melroy, NASA Deputy Administrator, after the impact. “But the best part was seeing at the end, that there was no question of going for a hit, and seeing the team happy with the success.”
The shot is expected to push Dimorphos into a tighter and shorter orbit around Didymus. Telescopes on Earth can time that orbit by watching how the amount of light from the double asteroid system changes as Dimorphos passes in front of and behind Didymus.
“It’s a really beautifully designed experiment,” says Boslough. In the coming weeks, dozens of telescopes across the continent will be watching Dimorphos to see how much DART has changed its orbit. The Hubble and James Webb space telescopes can also take pictures.
“It’s really interesting to see what comes out,” said Amy Mainz, a planetary scientist at the University of Arizona in Tucson, who is not involved in DART. “Asteroids surprise us,” he says, because it’s difficult to know the exact chemical makeup and internal structure of a space rock based on observations from Earth. Dimorpho’s post-throwing behavior is therefore exactly in line with the researchers’ expectations.
The missile team will compare the data on Dimorphos’ new orbit with their computer simulations to see how closely those models show the asteroid’s activity and behavior. “If we can collect our own examples of what happened, then you can use these examples.” [plan for] other missions that could show up in the future” — like the discovery of a real killer asteroid, says DART team member Wendy Caldwell, a mathematical physicist and planetary scientist at Los Alamos National Laboratory.
“Whatever happens,” he said, “we will have information that is valuable to the scientific community and the planetary defense community.”
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