AILSA CHANG, HOST:
All right. An asteroid about 7 million miles away has just been whacked by a NASA spacecraft.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED PERSON #1: Three, two, one.
UNIDENTIFIED PERSON #2: Oh, my gosh.
(APPLAUSE)
UNIDENTIFIED PERSON #3: Oh, wow.
UNIDENTIFIED PERSON #4: Awaiting visual confirmation.
CHANG: Now, this was a deliberate impact to see if the asteroid could be redirected onto a new path through space, basically a test to see if NASA could divert asteroids should one ever threaten our planet. NPR's Nell Greenfieldboyce has been monitoring this mission from its control center, which is at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. Hey, Nell.
NELL GREENFIELDBOYCE, BYLINE: Hey there.
CHANG: Hey. OK. So it sounds like everyone was pretty happy in there. What was the scene like?
GREENFIELDBOYCE: Well, people were happy at the end, but it was really tense. I mean, the spacecraft was flying itself at the end, so there was nothing for controllers to do but watch the photos it was sending back in real time as it got closer and closer. And in the images, the target asteroid went from looking like this little white dot in a black field to getting bigger and bigger and then looking like this gray rock with shading and texture. You could see boulders sticking up from it. It looked sort of spiky. And the last few moments were just really, really strange. You know, you were getting this close-up view of rocks on the asteroid's surface...
CHANG: Wow.
GREENFIELDBOYCE: ...That filled up the whole screen. And then suddenly, boom. The images cut out. Mission controllers declared impact, and that was it.
CHANG: Whoa.
GREENFIELDBOYCE: Everyone jumped up and was clapping and, you know, whooping it up.
CHANG: That is so cool. OK. So we don't know exactly what the moment of impact looked like - right? - like, whether it kicked up a bunch of debris or if it left a crater.
GREENFIELDBOYCE: So there's another small spacecraft that was nearby that took pictures, but those will take time to come back to the Earth - so, like, a few days. The asteroid that got hit is the size of a football stadium - something like that. So the impact likely kicked up a lot of rock. It got hit by this spacecraft that was going 14,000 miles per hour. But what the researchers all really want to know is how the asteroid's path through space changed.
CHANG: Well, how will they know that?
GREENFIELDBOYCE: So they have telescopes watching from all seven continents here on Earth and also in space like Hubble and James Webb. The asteroid that was hit orbits a larger asteroid. And what the telescopes will do is measure how long it takes to complete one orbit. And if the mission worked as planned, the asteroid will move closer to its big buddy and it will take less time to go around. So it's not gong to be a major change, just a little change.
CHANG: OK. So let's just be really clear here. This asteroid - I mean, it was no threat to Earth. But if there were a threatening asteroid, would this sort of, like, small change in path be enough?
GREENFIELDBOYCE: It would depend on the exact scenario, but potentially, yeah. I mean, NASA's goal is to find and track asteroids so that there's plenty of time to come up with a plan if there was one that looked like it had a high probability of hitting Earth. And when I say plenty of time, I mean like years, decades, even centuries.
CHANG: Right, right.
GREENFIELDBOYCE: So with that kind of advance warning, yeah, a little nudge could send it on a completely different journey that wouldn't approach Earth.
CHANG: Why can't you just blow up the asteroid like you see in movies?
GREENFIELDBOYCE: That's dramatic, but it's kind of frowned upon in the field of planetary defense...
CHANG: OK. Yeah.
GREENFIELDBOYCE: ...Because you might end up with a bunch of smaller but still hazardous asteroids headed your way.
CHANG: Good point. OK. So how concerned is NASA's about asteroids anyway?
GREENFIELDBOYCE: Well, they don't know of any current threats. You know, they've seen what big ones there are. There's no worrisome ones. But smaller asteroids, like ones that could take out a city - there's a lot out there that we haven't been tracking, that we haven't spotted. So NASA's just wants to get ready.
CHANG: That is NPR's Nell Greenfieldboyce. Thank you so much, Nell.
GREENFIELDBOYCE: Thank you.
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