IRA FLATOW: This is Science Friday. I’m Ira Flatow.

All summer and fall, we’ve been treated to spectacular photos from Pluto. And remember the first images that were beamed back by the New Horizons spacecraft? They just showed a tiny little dwarf planet– small, pixilated, brown dot. But boy, that was exciting.

And then we got closer. We saw the “whale tail”, and then the canyons, and the mile-high ice mountains– mile-high– came into focus. And for you Pluto geeks, the photos released this week, they’re going to knock you out. The high resolution photos were taken at the closest point– that’s about 7,000 miles away– and you can peer inside the craters. You can even see the ripples on the plains. And William McKinnon is a professor at Washington University in St. Louis– also the New Horizons Geology and Geophysics Deputy Lead.

Welcome to Science Friday.

WILLIAM McKINNON: Lovely to be here, Ira.

IRA FLATOW: How exciting are these things? I get tired of asking that question. Everything is, the next one’s even more exciting.

WILLIAM McKINNON: Well this is the apex. These are the highest resolution images, and they cut across the entire disk of Pluto. And we see stuff we’ve seen before at lower resolution, but this is the very best. It’s very exciting.

IRA FLATOW: All right. Let’s talk about the mile-high ice water mountains on Pluto. What details can you see from these high resolution photos?

WILLIAM McKINNON: Well, let me just say one thing. They’re not mile-high. They’re three-mile high.

IRA FLATOW: Oh, I’m cheating them out of their growth.

WILLIAM McKINNON: So they’re even more amazing. So you can see all sorts of amazing details. You can see the layers is on the sheer faces of the mountains. You can see how they’re jammed together, like logs at a dam. And they look like they’ve actually crushed smaller mountains and pieces of ice in between them. It speaks to some sort of really ancient cataclysm on Pluto.

IRA FLATOW: Wow– a cataclysm of what? Ice pushing against itself?

WILLIAM McKINNON: Well, we’re not really sure. It probably has something to do with large impacts but then also the evolution of the planet. Because Pluto is still an active body today. Which is, of course, one of the great findings of the whole mission– that we can travel to the ends of the solar system where the sunlight is very feeble and the surface temperature is very low. And we still see stuff happening, just like it’s Earth or Mars.

IRA FLATOW: Wow. And of course, there’s the question of why are there only mountains on one side of Pluto?

WILLIAM McKINNON: Ah, you are very perceptive. If I knew the answer to that, I’d write a paper right away.

[IRA LAUGHS]

It must have something to do, we think, with the contours of the–what we informally call– the Sputnik Planum Basin, which we think was ultimately created by a huge collision billions of years ago. But it’s probably deeper on one side and shallower on the other, and it basically must have let loose a lot of ice debris on one side.

IRA FLATOW: And there’s some sort of– one of the interesting photos here– that’s some sort of shoreline crashing into these mounds. And you can see, like, ripples.

WILLIAM McKINNON: Yeah, it’s amazing. All these mountains are jammed together, but then they stop. And that’s where this place Sputnik Planum starts. And basically, it’s a giant sheet of exotic ices.

Because on Pluto, water ice is like rock on the Earth, and on Pluto, what takes the place then of water vapor and liquid water and water ice is ices of nitrogen and carbon monoxide and methane. And there’s this great sheet, but when you get these super high resolution images where you can see basically things that are smaller than the length of a football field, you actually see that the surface is kind of fluted and rippled. And we don’t really know what’s going on.

Some people think it’s wind. But of course, Pluto has an atmosphere but not very much wind now, but maybe it had a thicker atmosphere in the past. Another idea is that these ices are still volatile. You know, solid nitrogen is pretty easy to vaporize, even at Pluto’s distance from the sun. And there may be a kind of sublimation pattern forming as the ice just sits there exposed.

IRA FLATOW: Is there more ice being added all the time? I mean, you look at all this ice, and you say three miles high. Where did all this water come from?

WILLIAM McKINNON: Ah, out there in the outer solar system, water and water ice, this is like the most important component of crusts and mantles of icy satellites and bodies like Pluto. But inside Sputnik Planum, and we actually see flow of what we call the glacial ices– the solid nitrogen and so forth– moving down out of the mountains and flowing onto the plains in that big, big basin.

And how this works is that basically the sunlight evaporates nitrogen gas, which then condenses elsewhere on the planet. And it piles up in a not too different way that snow piles up on the Earth and basically makes a glacier. And it goes downhill. It’s like there’s a cycle. And as this happens, it creates some of these fantastic landscapes.

IRA FLATOW: Wow. And now some of the great photos showing plains dotted with craters, and we can actually see inside these craters so well that we can see that there are different colored layers in the crater.

WILLIAM McKINNON: Yes. So you see dark layers, and then when you apply the color data we have, we can see that these layers are red. So there’s probably some organic matter involved. And you can go from– you could hop, literally– from crater to crater and see that you’re looking at the same layering. So basically, we’re looking at some sort of important substratum that is telling us about some event or compositional change in Pluto’s history. What that is exactly, we’ll have to work on in the months and years ahead.

IRA FLATOW: A lot of times when we see colors in/on the planets, we think there’s some sort of organic basis. Would that be true here too on Pluto?

WILLIAM McKINNON: Yes, because one of the common ices that’s on the very surface is solid methane, mixed in with the other stuff. And when you bombard it with radiation– which you get in outer space– it starts to make more complex organic molecules. And when you do this in the lab, it turns red. So that’s what we think it is.

There’s lots of red in the solar system. Sulfur can be red, and iron oxide on Mars can be red. But we think the red in the outer solar system has to do with these organic materials.

IRA FLATOW: Would that be true of the eye on Jupiter? The big storm?

WILLIAM McKINNON: That is one of the great mysteries of planetary science, is what makes the Great Red Spot red? The leading hypotheses have to do actually more with sulfur compounds or even phosphorous compounds. We don’t know yet. We’ll have to drop a probe in and find out.

[IRA LAUGHS]

IRA FLATOW: You know, it’s true. Every time I talk to scientists, they don’t want to know the answer because they want to keep the guessing going. They want to keep the trail hot if they–

WILLIAM McKINNON: Oh man, I want to know the answer.

[IRA LAUGHS]

IRA FLATOW: Well let’s talk about some more questions. Let’s talk about Pluto’s badlands. Can you describe the area called The Badlands?

WILLIAM McKINNON: Yeah. Well, if you fly over the frosty ice plains with the craters that we were talking about, all of a sudden, you come to a great cliff. It’s about a mile high. And this is actually part of a fault, a great fault system that has split part of Pluto apart. And then you’d basically end up in this very rugged, kind of dangerous-looking area.

We’re not exactly sure what went on there, but it looks like it’s been deeply eroded by various processes– so probably glacial, probably wind to some degree. And I wouldn’t be surprised if in Pluto’s distant past, there was even flowing liquid. But this liquid would probably be something like liquid nitrogen.

IRA FLATOW: So what I hear you saying is that Pluto is still sort of an active planet– oh, excuse me, subplanet.

WILLIAM McKINNON: Well, you know, dwarf planets are planets too. It’s part of a whole class of other bodies that everybody should know about. And they’re just as active. OK? That’s the beauty of going all the way out there and seeing all this. It could have turned out, I suppose, otherwise– just craters. But that’s not what’s there.

IRA FLATOW: Is there more data and photos coming in Is the drugstore still sending stuff back?

WILLIAM McKINNON: Absolutely. Absolutely. In fact, I just got the call yesterday. What I mean is more of these very, very high resolution photos are coming in tomorrow. And that will actually complete that set. Plus there’s really all sorts of other data– color data, spectral data that tells us the composition and all sorts of other things. We really probably only have about 25% of the total data down on the ground so far. The rest of it– the 75%– is still up on the spacecraft, and it’s going to take us almost another year to bring it all down.

IRA FLATOW: Any other photos from the other moons coming back, or are we done with them?

WILLIAM McKINNON: I think we have the best stuff from the other moons, at least in terms of landscape. But we have all sorts of other, more distant observations that help us understand the properties of the surface that people are looking forward to getting.

IRA FLATOW: Well, the good news is we’ve got another whole year to look at more photos– get more space–

WILLIAM McKINNON: We’ve got a whole year of great stuff to look at. Plus, we’re actually on target– if NASA approves– to explore an even further body in the Kuiper belt, which we will get to New Year’s Day in three years.

IRA FLATOW: Which is?

WILLIAM McKINNON: Well, right now we call it 2014 MU69. But it’s a small body in the Kuiper belt, and it’s part of our overall mission– not just to explore Pluto and its five moons, but to visit as many Kuiper belt objects as feasible.

IRA FLATOW: I hear the Star Trek music welling up in the background–

[WILLIAM LAUGHS]

–to go where no probe has gone before.

WILLIAM McKINNON: Well that’s exactly what we’re doing. It will, in fact, be the most distant body visited by the human race when we get there in three years.

IRA FLATOW: I cannot top that with anything. Wow. Thank you. Thank you, Bill.

WILLIAM McKINNON: Thank you.

IRA FLATOW: William McKinnon is professor at the Washington University in St. Louis. He’s also New Horizons Geology and Geophysics Deputy Leader. And you can see these photos of Pluto on our website. They are fantastic at ScienceFriday.com/Plutophotos.

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