< NASA launches 1st-ever practice mission to defend Earth from asteroids

AUDIE CORNISH, HOST:

Back in the summer of 1998, there were not just one, but two different action movies in which Earth is threatened by asteroids.

(SOUNDBITE OF FILM, "ARMAGEDDON")

UNIDENTIFIED ACTOR: (As character) I think one's about to hit near Paris.

(SOUNDBITE OF EXPLOSIONS, PEOPLE SCREAMING)

CORNISH: "Armageddon" and "Deep Impact" were science fiction. But what if an asteroid actually were headed in our direction? Well, NASA is developing a plan for that. And this week saw the launch of the Double Asteroid Redirection Test, or DART for short. Its mission? To alter the path of a small asteroid.

With us now is Lindley Johnson, NSA (ph) planetary defense officer. Welcome to the program.

LINDLEY JOHNSON: Thank you. Glad to be here.

CORNISH: First, let's start with this particular asteroid, why you're targeting it. Because I understand it's not really a threat to Earth right now.

JOHNSON: No, it's not a threat to Earth at this time. In fact, we don't have any known threat to Earth. But it is a very good natural laboratory for doing this test. It's a binary asteroid system in orbit around the sun, just like the Earth is, and the - has a moonlet that orbits it. So we can do this test against the moonlit, Dimorphos, without changing the orbit of the - Didymos around the sun so it doesn't...

CORNISH: I'm going to stop you there 'cause now we're getting into planetary language I don't (laughter) necessarily understand.

JOHNSON: (Laughter).

CORNISH: But it sounds like what you're saying is you are going to target this asteroid's moon to help redirect it. How will that work? And am I getting that right?

JOHNSON: Yeah, if we don't need to change the orbit of Didymos - in fact, we don't want to. We want it to stay in the same orbit it is around the sun. But we're proving this technology by impacting the moon and changing its orbit.

CORNISH: How will you know if it works?

JOHNSON: We have ground-based observatories that have been observing the double asteroid for, well, actually many years, so we understand the orbit of the moon. We have it timed down to exactly how long it takes to orbit. It's 11 hours and 55 minutes. After the impact, we will take the same measurements of the orbital period and see what the difference is.

CORNISH: Can you talk about why this is the first mission of its kind?

JOHNSON: Well, it's the first planetary defense mission because we have just, in the last few years, started a planetary defense program at NASA. It wasn't until the 1980s or so that we understood that there's still a large number of asteroids that can come near Earth's orbit. So we have spent since 1998 surveying the skies. And by 2010, we had discovered what we think is at least 90% of the large, very large, asteroids - one kilometer or larger in size - that can come close to Earth's orbit and also big enough to do significant damage if they were to impact.

CORNISH: It's funny you should mention 1998 because obviously in our introduction, we talked about these films - right? - which had this as a plotline. And in these movies and the ones that have followed, it never works. So is that weird for you, like, (laughter) I guess, since this is your actual job?

JOHNSON: Well, that's because that's Hollywood doing it. We're NASA, and we're working with our international partners, other space agencies that are making contributions to the effort as well. That's why we're doing this test to prove out the technology - because we don't, you know, want to be doing it for the first time when there is a real impact threat.

CORNISH: Well, Lindley Johnson, thank you so much for the work you do and thank you for speaking with us.

JOHNSON: Oh, very glad to do it. Thanks for having me.

(SOUNDBITE OF FOXYGEN'S "STAR POWER I: OVERTURE")

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