DAVID GREENE, HOST:

An unmanned NASA space probe is just about an hour away from flying past Pluto. This is the first time a spacecraft has ever been to Pluto, and it has taken almost a decade to get there. Joining me on the line from mission control at the applied physics laboratory in Laurel, Md., is NPR science correspondent Geoff Brumfiel.

Geoff, good morning.

GEOFF BRUMFIEL, BYLINE: Good morning, David.

GREENE: So it's only been a decade (laughter). I mean, there has to be a lot of anticipation there. What is the latest on this mission?

BRUMFIEL: So this spacecraft, as you said, it's been on - it's been flying for about a decade, and it's now about an hour away from being 8,000 miles from the surface of Pluto. Now, 8,000 miles might sound like a long way away to earthlings, but you have to remember it's 3 billion miles to get to Pluto, so this is very, very close. And all the spacecraft's instruments are designed to give great pictures and scientific measurements at 8,000 miles, so we really should be seeing some amazing stuff here.

GREENE: So before we get to that, I mean, I'm just thinking - 3 billion miles, 10 years this thing has traveled. It has to be an amazing spacecraft. I mean, can you tell me what it looks like, what it is?

BRUMFIEL: Yeah, yeah. It's actually - it's a plucky, little thing. It's called New Horizons. It's about the size of a baby grand piano. And part of the reason it's so small is that they had to fling it away from Earth as fast as they could just to get it there within a decade. It's moving at 30,000 miles per hour relative to Pluto, and at those speeds, it's not going to be able to stop. It's just going to go sailing past Pluto. Now, the spacecraft is, like, a little sort of triangular thing, I guess, with a big radar dish on top. It's not much to look at, but it's doing some pretty cool stuff.

GREENE: So paint a picture of where exactly you are and what the atmosphere is like in the control room.

BRUMFIEL: Right. So I'm here sort of near the control room. And here's the funny thing about this mission, OK? It's so far away that it's actually going to take four and a half hours for the signals from Earth to reach the spacecraft and the signals from New Horizons to reach Earth. And at those kinds of distances, even if they decided, hey, we want to take an extra close-up of this thing, by the time they sent the command there, the spacecraft would be gone. So everything's on autopilot. The spacecraft's doing its own thing. And people here on the ground are just frankly waiting around. And what they've done is they've invited family members. They've invited the relatives of Clyde Tombaugh, who discovered Pluto, to come here. And it's really actually kind of a festival atmosphere while everyone waits to hear back.

GREENE: Waits to hear back - well, what - I mean, that must be a little scary if the thing sort of, you know, coming to this important moment and doesn't get back in touch, I'd imagine?

BRUMFIEL: Yeah, I mean, you know, I've been asking about that. They have a lot of confidence. They've had nine and a half years to work out all the bugs, although they did encounter one little computer crash right before they got here. But basically, you know, things are looking pretty good. We'll have to wait until tonight. There is a small chance, as it passes between Pluto and its moon Charon, it could be struck by a rock, and that could be the end of it. But assuming it isn't, then we're going to hear a signal late tonight. All it's going to say is I'm OK, I made it. And then it's going to go right back to taking measurements. It's actually going to take months and months to get the data back.

GREENE: All right. Geoff, sadly we'll have to stop there. We'll be watching this Pluto mission come together. NPR science correspondent Geoff Brumfiel. Transcript provided by NPR, Copyright NPR.