NASA’s first planetary defense mission will nudge an asteroid

Intentional crash of robotic probe will test way to avert asteroid impacts on Earth

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Bits of heavenly debris rain down continuously into Earth’s atmosphere, with the vast majority being so tiny they burn up. Fragments sometimes make it to the surface as meteorites—and on rare occasions they are large. Most famous is the city-size asteroid that took out the dinosaurs 66 million years ago, leaving an enormous scar buried off the coast of Mexico’s Yucatán Peninsula.

NASA has catalogued more than 90% of these 1-kilometre-or-bigger potential killers and has shown that none endangers our world anytime in the coming centuries. But the agency has yet to discover all the smaller threats. Even a 160-meter-wide asteroid can do major damage, says Elena Adams, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory and DART’s systems engineer. “A city like Manhattan would be completely obliterated,” she says.

Over the years, researchers have proposed multiple ways to deal with the threat of deadly asteroids: vaporizing them with lasers, changing their course using the gravitational pull of a spacecraft, or detonating a nuclear bomb near them. DART will attempt one of the simplest options—hitting them and redirecting their orbit.

After launch, DART will unfurl its solar panels and spend about 10 months cruising to a pair of objects named Didymos and Dimorphos. The larger body, Didymos, is about 780 meters across. DART’s target is Dimorphos, about 160 meters in diameter. Scientists chose to go after the smaller object in part because it’s gravitationally bound to Didymos like a moon; DART’s nudge is unlikely to accidentally send it on a collision course with Earth.

DART only has one real instrument, a high-resolution imager that will beam pictures back to researchers. About 1 month before it reaches the binary pair, the camera will spot Didymos for the first time and navigate toward Dimorphos, Adams says. Some 10 days before impact, the spacecraft will deploy a small CubeSat, built by Italy’s space agency, to trail behind and record the aftermath. DART will become fully autonomous 4 hours prior to its self-destructive plunge.

DART will scream into its target at more than 6 kilometres per second, 10 times faster than a fighter jet and fast enough to leave a crater 10 to 20 meters across. Because Dimorphos moves around its parent at a leisurely half-kilometre per hour, the collision should kick the moonlet into a shorter orbit, a change that will be measured by radar instruments on Earth. Images from the Italian CubeSat will allow scientists to study the plume and the resulting crater, providing information about the asteroid’s composition.

Exactly how much DART nudges Dimorphos depends on many things. The spacecraft could come down on top of a rock, blowing that rock to smithereens but transferring little momentum to the asteroid, Schultz says. Or it might strike at an angle that doesn’t maximize the force it imparts, he adds. Many asteroids are thought to be loosely bound rubble piles, in which case DART could end up scattering a cloud of rocks.

Another source of data will be the European Space Agency’s (ESA’s) Hera mission, which should reach the asteroid duo in 2026 after launch 2 years earlier. Hera will carry an altimeter, several cameras, and two more CubeSats. The mission was supposed to arrive with DART, but it was delayed after ESA initially declined to fund it in 2016.

Although researchers will learn about DART’s target, science isn’t the goal of the mission, which was sponsored by NASA’s Planetary Defense Coordination Office. “It’s different from your typical science mission where your object is to publish as many papers as possible,” Adams says. “This is to demonstrate a technique to save the world.”

By Adam Mann and originally appeared in Science.Org