The NASA spacecraft will collide with asteroids in the first planetary defense test

NASA is launching a multi-million dollar spacecraft – and slamming it into an asteroid. Instead of being a catastrophic failure, however, it will be the first test of a way to protect Earth from lethal asteroids.

The asteroid that NASA smashes into, called Dimorphos, is not a threat to Earth. But scientists want to see if they can change its orbit long before they might have to use such a strategy to deflect a really dangerous asteroid.

“The chances of something big enough to be a problem that we will have to deflect are quite small in our lifetime,” says Andy Rivkin, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory (JHU-APL) in Laurel, Maryland, who built the spacecraft for NASA. “But sometimes your number shows up when you don’t expect it, and it’s good to have insurance.”

The spacecraft scheduled to launch from California on November 23 is called the Double Asteroid Redirection Test (DART).1. Its target is a pair of asteroids traveling together through space, with one orbiting the other while orbiting the Sun (see ‘A less gentle push’). Dimorphos, the smaller of the two with a width of 160 meters, orbits Didymos, which is almost 5 times larger and is named after the Greek word for ‘twin’.

A NOT SO MUCH NUDGE.  Graphic depicting the Double Asteroid Redirection Test (DART) mission taking place in 2022.

Credit: Adapted from NASA / Johns Hopkins University APL

If DART is successfully launched, it will hit Dimorphos at 6.6 kilometers per second in late September or early October next year. The impact should shrink Dimorphos’ orbit so that it orbits Didymos at least 73 seconds faster than before. (Dimorphos is named after Greek for ‘having two shapes’, to signal NASA’s intention to change the asteroid’s orbit.) Astronomers using telescopes on Earth will see Didymos for signs of that orbit change – which would be clear in that way , its brightness changes over time as Dimorphos passes in front of and behind it.

This intricate choreography is meant to test the idea that smashing into an asteroid can give it a push enough to prevent it from hitting Earth, says Nancy Chabot, a planetary scientist at JHU-APL working on the mission. Using the non-threatening pair of Dimorphos and Didymos is “a really smart and safe way to perform this first test,” she says. The impact will occur when the asteroids are 11 million kilometers from Earth.

Fighting asteroids

Small asteroids and asteroid fragments hit the Earth all the time, but most of them dissolve in the atmosphere or fall harmlessly to the ground like meteorites. NASA has identified more than 27,000 asteroids with orbits that bring them close to Earth. The concern is that a new asteroid could emerge with course directly towards the planet – and that it would be large enough to cause serious consequences when it hits, just like with the asteroid that helped kill the dinosaurs and other life on Earth 66 mio. years ago.

Space scientists have hovered all sorts of ideas to fight incoming asteroids, the most dramatic of which involves blasting them with nuclear weapons2. Other, less cinematic strategies involve changing the orbit of the asteroid by flying a spacecraft next to it to pull it by gravitational forces, or smashing into it, as the $ 330 million DART mission will.

Members of the DART team at APL inspect the spacecraft in a clean room.

Scientists at the Johns Hopkins University Applied Physics Laboratory are inspecting the DART spacecraft during testing in July.Credit: Ed Whitman / NASA / Johns Hopkins University APL

Depending on the angle at which the DART hits the asteroid, it can kick up a small cloud of dust and debris. The impact will likely leave a crater that may be about 10 feet in diameter. At the same time, pieces of the spacecraft’s wreck can be scattered across the asteroid’s surface, but exactly how the DART will break apart is still unknown. “Just from a pure crime scene sense, many of us are curious about it,” Rivkin says.

Scientists will have a chance to get an answer, because a few minutes later a small probe funded by the Italian space agency will fly by to photograph the aftermath3. The one called LICIACube will travel aboard the DART and is the agency’s first self-guided deep space mission. LICIACube is released from DART 10 days before impact and arrives within 55 kilometers of Dimorphos. As it whizzes by, its cameras should spot the dust cloud if the shock hits one, and possibly the resulting crater. “We may be surprised by the images we collect,” said Elisabetta Dotto, an astronomer at the National Institute of Astrophysics in Rome, who heads the collaboration between Italian universities and institutions involved in LICIACube.

In 2026, a follow-up spacecraft, the European Space Agency’s Hera mission, will visit Dimorphos to take more detailed pictures of the crash site.

Data collected by the DART mission should help scientists understand how impacts affect asteroids, says Megan Bruck Syal, a physicist at Lawrence Livermore National Laboratory in California, who will model what happens to Dimorphos. But DART is just one test that involves one kind of space stone. There may be scenarios where planetary defenders want to hit an asteroid at more speed than DART reaches when it hits Dimorphos, or where they have to hit an asteroid with several impactors to change its course. “We need to do more experiments like this,” says Bruck Syal.

Although many other spacecraft have been deliberately smashed into celestial bodies at the end of their lives, DART promises to be the first to hit a planetary body in the name of saving Earth.

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