NASA's DART spacecraft will smash into asteroid to test planetary defense tool NASA is about to launch the first mission of its new planetary defense office. A spacecraft will attempt to knock a small asteroid off course by ramming into it.

In a first test of its planetary defense efforts, NASA's going to shove an asteroid

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STEVE INSKEEP, HOST:

Next, we have a bit of news from space. A NASA spacecraft set to launch this week will try to change the trajectory of an asteroid, which could come in handy if Earth is ever threatened by a rock from space. It was put together by NASA's Planetary Defense Office, which is a real thing.

NPR's Nell Greenfieldboyce reports.

NELL GREENFIELDBOYCE, BYLINE: NASA keeps watch on the biggest asteroids around Earth. For the foreseeable future, none are a threat. But there are plenty of smaller rocks - the size that could take out a city - that still haven't been found and tracked. The space agency is working on a new telescope to search for more. And it's also about to make its first-ever attempt to knock an asteroid off course.

Nancy Chabot is this mission's coordination lead. She's a scientist at the Johns Hopkins University Applied Physics Laboratory.

NANCY CHABOT: A lot of times when I tell people that NASA is actually doing this mission, they kind of don't believe it at first, maybe because it has been the thing of movies.

(SOUNDBITE OF FILM, "ARMAGEDDON")

BILLY BOB THORNTON: (As Dan Truman) It's the size of Texas, Mr. President.

(SOUNDBITE OF ASTEROID TRAVELING THROUGH SPACE)

THORNTON: (As Dan Truman) It's what we call a global killer - the end of mankind - half the world incinerated by the heat blast.

GREENFIELDBOYCE: You know, movies like "Armageddon," which featured Bruce Willis trying to blow up an incoming asteroid with a nuclear bomb - there won't be quite as much drama with NASA's Double Asteroid Redirection Test, or DART.

CHABOT: So DART is demonstrating asteroid deflection. It is absolutely not asteroid disruption, which is how it goes a lot of times in the movies.

GREENFIELDBOYCE: Rather than trying to obliterate an asteroid, DART will just give one a little nudge, by ramming a spacecraft into it. Have no fear; the target asteroid is no danger now, and there's no chance that this mission could send it careening towards us.

CHABOT: There is absolutely no way that the DART pest is a threat to the Earth.

GREENFIELDBOYCE: Chabot says the DART spacecraft will travel over 6 million miles to a big asteroid that's orbited by a smaller asteroid. It's the smaller one that's the target. This space rock is about 500 feet across.

CHABOT: And so it's like a small golf cart running in to a Great Pyramid.

GREENFIELDBOYCE: Except this golf cart will be going 15,000 miles per hour. The impact will happen next autumn.

Elena Adams is a mission systems engineer at the Applied Physics Laboratory. She says in the last few hours, she and her colleagues will simply watch and wait as the spacecraft hones in on its target, sending pictures back to Earth as it gets closer and closer.

ELENA ADAMS: It is four hours of watching paint dry but kind of terrifying at the same time because the spacecraft's completely autonomous.

GREENFIELDBOYCE: In the final seconds before impact, scientists will get their first good look at this space rock. It's so small and so far away the telescopes can't really see it. Instead, they see this pair of asteroids as little more than a point of light. But it dims whenever the small asteroid passes in front of its larger companion. It normally orbits once every 11 hours and 55 minutes. But the impact should slightly shorten that time period. By how many minutes, no one knows.

Adams says everyone will watch closely.

ADAMS: And just see, how does it react to being pushed?

GREENFIELDBOYCE: She says this test should help NASA understand what its options are if it ever spots a space rock headed this way.

Nell Greenfieldboyce, NPR News.

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