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An artistic rendering of the DART spacecraft approaching Dimorphos
Image: NASA/John Hopkins APL

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NASA wants to defend Earth from asteroids — so it’s slamming a spacecraft into one

Takeoff of DART is scheduled for 1:21AM ET on November 24th

Late this evening, NASA is launching a spacecraft the size of a refrigerator, sending it on a crash course with an asteroid in 2022 — and it’s all on purpose. This intentional self-destruction will tell us if slamming a spacecraft into an asteroid is enough to save Earth in the future if a massive space rock is headed our way.

The mission is called DART, or the Double Asteroid Redirect Mission, and its purpose is in the name. The spacecraft is going to try to redirect an asteroid in space for the first time. The idea is pretty simple: DART is going to ram into the object moving at roughly 15,000 miles per hour, transferring its momentum to the asteroid. This body slam should be enough to deflect the asteroid off its original path by a fraction of 1 percent. The asteroid DART is targeting doesn’t pose any threat to Earth, and there’s nothing the mission can do to change that. NASA just wants to see if bumping a space rock well ahead of time could change its direction enough so that over the long-term, it would whiz by a planet safely instead of hitting it.

It’s a type of technique that we couldn’t have really considered 30 years ago, but with recent advances in technology, it might just be an option for saving the planet one day. “We’ve got the ability, with current technology, to be able to at least start to make asteroid impacts a preventable natural disaster,” Tom Statler, the program scientist for DART at NASA, tells The Verge.

Planetary Defense

A significant part of NASA’s overall charge is the concept of planetary defense: protecting Earth from asteroids or other space objects that might cross paths with our planet. It’s also the part of NASA’s mission that seems to capture the imaginations of the general public and Hollywood the most. Films like Armageddon and Deep Impact have envisioned various ways that NASA might try to stop an asteroid or comet heading toward our planet. Both of those films, though, see humans traveling to the space rock that would cause our impending doom — a scenario that would most likely never happen because of the immense complexity and safety issues such a mission would pose.

In Armageddon, humanity discovers an asteroid the size of Texas just 18 days away from hitting the planet. Such short notice for a planet-killing asteroid is also unlikely, as NASA is on a constant search for such rocks. Right now, our biggest workhorse asteroid hunters are the two Pan-STARRS telescopes in Haleakala in Hawaii, which scan the sky for asteroids we haven’t found yet. Once the rocks are spotted, scientists can figure out their paths around the Sun to see if they might ever intersect with our planet. So far, there are no asteroids that we know about that will pose a hazard in the next 100 years, and we’ve found most of the largest ones that could cause global devastation.

The vapor trail left by the Chelyabinsk meteor
Image: Alex Alishevskikh

However, it’s still possible that we could be surprised one day. NASA believes it has found only about 40 percent of all near-Earth asteroids that are larger than 140 meters, or 460 feet, across — the ones that would do unthinkable destruction if they were to hit a populated area. And we’ve been surprised by dangerous space rocks before. In 2013, a meteor the size of a house blasted apart in the skies over Chelyabinsk, Russia, without any warning, causing an explosion similar to 440,000 tons of TNT and injuring more than 1,600 people.

The Chelyabinsk meteor was thought to be just 18 meters, or 60 feet, across, and it still did major damage. That’s why NASA is really eager to find asteroids that are between 140 and 150 meters across. An impact from one could lead to mass casualties, refugee crises, political instability, supply chain disruptions, and more. “If the impact were in a populated area or a technology center, that could be very severe,” says Statler. “Even if the direct effects were very localized, it could have worldwide effects.”

The nudge

To prevent such a nightmare scenario, scientists have floated lots of different ideas. Some have suggested sending nuclear devices into space to either destroy a hazardous asteroid or blow up near it to create a shockwave that would knock it off course. However, launching nukes into space is tricky to navigate, considering their use in space is prohibited under international law. Plus, it’s just incredibly difficult to actually blow up asteroids, which are typically moving through space at upwards of 40,000 miles per hour.

NASA scientists think simply nudging an asteroid when it’s still relatively far from us is an easier solution. But NASA has never tried pushing an asteroid off its course before. With the DART mission, the space agency is starting off small. The mission is heading toward an asteroid named Didymos, which is about 2,500 feet wide or roughly the height of the Burj Khalifa, the world’s tallest building in Dubai. But that’s not the spacecraft’s end target. DART is actually going to smash itself into a moonlet asteroid that orbits around Didymos, called Dimorphos, that’s about 525 feet, or 160 meters, wide. The collision will transfer enough momentum to change Dimorphos’s orbit around the larger rock.

Radar images of Didymos and its moonlet taken in 2003.
Image: NASA

The problem, though, is we’ve actually never seen Dimorphos before. We just know that it’s orbiting around Didymos because it periodically passes in front of the asteroid, slightly dimming the light bouncing off the larger rock. Based on that dimming, scientists know the moonlet’s approximate size and the time it takes to orbit Didymos. The DART spacecraft — which will weigh 550 kilograms or 1,210 pounds at impact and is shaped like a big box — is expected to change the time it takes Dimorphos to orbit Didymos by at least 73 seconds, if not several minutes, after slamming into the moonlet. It’s a process that will lead to the complete destruction of DART, what Statler refers to as an “extreme smithereen-ing event.”

But we really have no idea what kind of asteroid we’ll find when we get there, which creates uncertainty about exactly what will happen to Dimorphos. In fact, the asteroid is so small and dark that DART mission engineers may not see it until just an hour before the spacecraft hits.

“The thought right now is that it’s made out of the same thing as the main asteroid, but we don’t have any real proof of it because we don’t know anything about that moon,” Elena Adams, the DART mission systems engineer at John Hopkins Applied Physics Laboratory, tells The Verge. Based on past missions to asteroids, NASA is realizing that the surfaces of some asteroids are very fluid and crushable, almost like liquids. How that kind of material responds to an impact from a spacecraft like DART is unknown.

The good news is we should be able to see DART’s destruction. Just before impact, the main spacecraft will deploy a tiny spacecraft the size of a cereal box that will pass by Dimorphos three minutes after impact and record the resulting plume from the smash. That way, we’ll be sure that DART did its job.

Did it work?

Measuring a slight change in an asteroid’s path is no easy feat. But NASA has a plan for this. In the days and weeks following DART’s demise, astronomers will use telescopes to observe Didymos and Dimorphos, watching as the moonlet periodically dims the main asteroid. If the timing of those dims changes over time, that means the moonlet’s orbit has been altered and DART did its job.

For a more detailed look at how DART affected the Didymos system, the European Space Agency will launch a spacecraft called Hera in 2024 that will meet up with the binary pair in 2026. The mission will do a complete survey of the system to map out DART’s impact.

SpaceX’s Falcon 9 rocket in California, with DART on top
Image: NASA/Bill Ingalls

If DART turns out to be a success, imparting just a tiny change to the orbit of Dimorphos, that could jumpstart discussions about how to deal with a hazardous asteroid in the future. Perhaps we could bank a bunch of DART-like spacecraft on the ground, ready to deploy when we find an asteroid heading toward us. “It’s a broad discussion, inside and outside of government, to figure out how prepared do we want to be?” says Statler.

Before that happens, DART has to meet its fate, and that all begins with a launch. The spacecraft is set to take off on top of a SpaceX Falcon 9 rocket out of Vandenberg Space Force Base in California at 1:21AM ET on Wednesday, November 24th. For the mission team, it’s a bittersweet moment as they say goodbye to their spacecraft, sending it toward its doom. But it’s also a pretty cool experience. “I mean, how often do you get to crash $250 million spacecraft, right?” Adams says. “Not very often.”

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