NASA is about to launch a craft designed to crash itself directly into a hurtling space rock at 15,000 mph.
If weather cooperates, NASA’s Double Asteroid Redirection Test mission, known as DART, will blast off early Wednesday morning atop a SpaceX Falcon 9 rocket at Vandenberg Space Force Base, northwest of Santa Barbara, California. DART will target a small near-Earth asteroid called Dimorphos, which is orbiting a much larger asteroid. Next fall, after a journey of some 6.8 million miles, the craft will smash into Dimorphos and slightly change the rock’s trajectory. It’s a test of what could be done to save the world from an asteroid on a potentially deadly collision course with us, to prevent the kind of planetary catastrophe envisioned in movies like Armageddon and Deep Impact.
The launch window opens at 1:21 am Eastern time on November 24, and the takeoff will be streamed on NASA TV. A cold front is approaching near the area, with some light winds, but officials still estimate a 90 percent chance of launch-friendly conditions, said Captain Maximillian Rush, a weather officer at Vandenberg Space Force Base, at a news briefing on Monday. If they have to delay for a day, he expects a 100 percent chance the weather will cooperate on Thursday.
“DART is the first mission devoted to planetary defense, to do something about an asteroid threat, to prevent it from hitting the Earth if you needed to,” says Nancy Chabot, the DART coordination lead and a planetary scientist at Johns Hopkins University’s Applied Physics Laboratory, which developed the craft in partnership with NASA. Dimorphos and the larger asteroid it orbits are not a threat, she quickly adds. “This is just a test.”
And DART has only one shot at it. The spacecraft’s basically a box, 4 feet across, with long solar panels on each side, and it needs a direct hit on Dimorphos, which is itself approximately 500 feet wide—about the size of the Great Pyramid of Giza. From Earth, the asteroid pair looks like a single faint dot in the sky. As DART careens toward them, its optical camera will feed images to the onboard Smart Nav guidance system. That includes an algorithm that automatically navigates the craft, rather than depending on commands from engineers on Earth, because there’s too much lag time over such long distances.
As it approaches, scientists will get a better idea of DART’s estimated date of impact, likely between September 26 and October 1 next year. About 10 days before arrival, it will deploy a briefcase-sized CubeSat called LICIACube, developed by the Italian Space Agency, which will snap photos of the cosmic collision and the resulting rocky debris, and send the images home.
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While Dimorphos resembles many other near-Earth asteroids, the DART team chose it as a target because it’s the junior member of an asteroid binary. It’s called a “moonlet,” and it orbits Didymos, its larger partner, like clockwork every 11 hours and 55 minutes. DART will hit Dimorphos at an angle of about 17 degrees with respect to its orbit, and scientists plan to measure how much its orbit consequently gets shifted. In other words, they can easily compare its motion with that of another nearby body. If they had chosen to strike a solitary asteroid, the minuscule deflection to its orbit wouldn’t be evident for years, until it made a close pass by the Earth. But thanks to the proximity of its partner, any alterations to the orbit of Dimorphos can be determined within days.
“It’s really a smart and clever way, and it’s cost effective. And it’s also safe: You’re nudging this moon a little close to the asteroid it already orbits,” Chabot says. She and her team expect DART to shorten the asteroid's orbit by five to 15 minutes, so that it might only take 11 hours and 45 minutes to go around Didymos. NASA will consider a deflection of 73 seconds or more to be a successful mission.
The asteroid pair will be close enough for precise measurements with telescopes on Earth until March 2023. After that, they will travel farther away, as part of their path around the sun extends beyond the orbit of Mars. While the asteroids look like a single point of light from this distance, scientists will be able to measure how frequently the brightness of the reflected sunlight that bounces off Didymos dims—a proxy for the duration of Dimorphos’ orbit.
These asteroids, like many others and some meteors—space rocks that enter Earth’s atmosphere—aren’t dense and solid like billiard balls. They might be chunks of rock, gravel, and ice loosely held together in an arrangement called a “rubble pile,” with a stony composition similar to the asteroids Ryugu and Eros, and to the meteor that burst over Chelyabinsk, Russia, in 2013. In fact, the Dimorphos moonlet may have formed simply by spinning off the side of Didymos. If Dimorphos is rubbly, DART’s impact could make a crater, rather than flinging debris and significantly nudging the asteroid. But that uncertainty is one of the reasons for performing the mission.
For a more detailed inspection of the crash scene, the European Space Agency’s Hera mission comes next. The spacecraft is scheduled to launch in 2024. When it reaches the asteroidal duo in 2026, its optical camera, lidar tool, infrared scanner, and two CubeSat sidekicks will make detailed maps of Dimorphos’s surface and structure.
If a hazardous asteroid is ever actually bearing toward Earth, slamming a spacecraft—or a “kinetic impactor”—into it is just one tool at humanity’s disposal. NASA, ESA, and other space agencies have also been exploring other approaches, like positioning a spacecraft close by as a “gravity tractor” to pull it onto a different course, or detonating a nuclear explosion nearby to force it away. (Nuking the asteroid itself risks failure, since that could turn it into many rocks without changing their path by very much.) “The kinetic impactor is by far the most mature of these techniques,” said Lori Glaze, the director of NASA's Planetary Science Division, at a media briefing on Sunday.
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Among NASA’s priorities, climate science and efforts to monitor objects that could collide with the Earth enjoy the most public support, according to a recent poll of American adults. The agency has focused on the latter for years through the Planetary Defense Coordination Office. The DART mission constitutes a major milestone for that office, and for international collaboration, as the first attempt to deflect an asteroid.
But before NASA can actually deflect hazardous asteroids, the agency has to find them. In 2005, Congress mandated that NASA catalog most asteroids the size of Dimorphos and larger. A handful of comets make the list too, since there’s a small risk of a collision with one, a scenario portrayed in the upcoming movie Don’t Look Up. (Don’t worry, there are no known cases of impacts by rogue planets, like in Melancholia.) “At this moment, we are not aware of a single body that could hit the Earth during the next hundred years,” says Thomas Zurbuchen, NASA’s associate administrator for science. But he acknowledges that there could be others that haven’t been found yet.
So far, scientists believe they’ve detected about 90 percent of the near-Earth asteroids half a mile across or larger—the planet-killing variety. They’ve only managed to find about 40 percent of the smaller, Dimorphos-sized ones, which wouldn’t destroy our world but could still cause regional devastation across a whole continent.
“The real challenge for a lot of these asteroids is: You have to look where they spend most of their time,” says Joseph Masiero, a planetary scientist at Caltech. He’s involved with NASA’s Neowise telescope collaboration, which has discovered a number of near-Earth asteroids and added them to the list. He’s also working on NASA’s planned NEO Surveyor probe, which will find even more. It’s currently scheduled to launch in the first half of 2026.
Masiero likens the search for near-Earth objects to a racetrack, with our planet one of the race cars speeding around it. An asteroid that might eventually collide with us likely has a similar orbit to ours, but it could spend most of its time on the opposite side of the track, where it’s small, faint, and hard to see.
While scientists can project an asteroid’s path decades into the future, that path can change. That sometimes happens when an asteroid’s orbit takes it close to the sun, where it absorbs some light and re-emits it as heat, giving it a slight push. That phenomenon is known as the Yarkovsky effect, and it’s why most asteroid-finding telescopes focus on infrared wavelengths, capable of scanning for that heat signature of re-emitted light.
The advantage of having an early warning if an asteroid is on a collision course is that only a tiny shift in trajectory would be needed to save the day—and the DART mission is a dry run at doing that. It will be perhaps the only time NASA scientists will celebrate the destruction of one of their spacecraft. DART will continually stream images back to Earth, showing the tiny dot representing Didymos and Dimorphos as it grows in size and brightness, with the last image of the asteroids being sent back a few seconds before the crash, Tom Statler, DART program scientist, said at the briefing on Sunday. “We’ll have a confirmation by the loss of signal that the spacecraft impacted,” he said. “And I’m sure at that moment, everyone will give a big cheer and some high fives.”
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