Imagining A More Active Moon

The standard picture of the moon is of a long-dead object, geologically speaking. But using observations from cameras on board the Lunar Reconnaissance Orbiter, Thomas Watters and colleagues say in the journal Nature Geosciencesthat there are signs of more recent tectonic activity on the moon, within the last 50 million years.

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IRA FLATOW, HOST:

This is SCIENCE FRIDAY. I'm Ira Flatow. When you think about the moon, once you get pass thinking about Apollo, the moonlit romance, maybe cheese, your next thought is: so what? It's a big rock, a gray, dead place. But new research hints that the moon may not be as dead geologically as we might think. That on the far side of the moon there are signs of tectonic activity, recent, within the last 50 million years - counts as recent in geological time. Joining me now to tell us all about it is Tom Watters, one of the authors of that report published this week in the journal Nature Geoscience.

He's a senior scientist at the Center for Earth and Planetary Studies at the Smithsonian National Air and Space Museum in Washington. Welcome back to the program, Tom.

DR. THOMAS WATTERS: Hi, Ira. It's a pleasure to be back.

FLATOW: You're very welcome. Tell us what are these - what's the evidence of recent 50-million-year-old tectonic activity on the far side?

WATTERS: Well, it's an interesting story, and it starts, not quite two years ago when I was on before, and talked about the shrinking moon that we had located using very high-resolution images obtained from the Lunar Reconnaissance Orbiter, which has been in orbit around the moon since 2009. We saw these features, these land forms that indicate that the lunar crust was actually shrinking. It was being contracted and forming these fault scarps. So we went looking for more of these.

Now that we are continuing to get more and more coverage of the moon with these very high-resolution images, and we found something we weren't expecting. We found just the opposite of the type of land forms that indicate contraction. We found land forms that indicate that the moon is actually expanding and being stretched and pulling apart - not by much, but a little bit. And these features actually are very narrow, very relatively long troughs that are formed when the crust of the moon is being pulled apart and just breaks and then a section of it drops down.

FLATOW: Wow. Wow. And what would be pulling it apart?

WATTERS: Well, that's an excellent question, and it's one of the really interesting aspects of the research that we need to continue to do because we're not exactly sure what is causing this stretching within these small areas because, again, here we've had this picture of a now contracting moon. We have evidence for these global contractional faults, and here now we have evidence of...

FLATOW: Stretch marks.

WATTERS: Yes. Exactly.

(SOUNDBITE OF LAUGHTER)

FLATOW: Stretch marks. You didn't want to say it, so I said it for you.

WATTERS: Yeah. It's funny. You know, you wrack your brain thinking about creative ways of describing, you know, technical jargon, and...

(SOUNDBITE OF LAUGHTER)

WATTERS: ...stretch marks never occurred to me. But it's actually a very appropriate, very accurate way of describing these things. So, yeah, we're trying to figure out what are the forces that are acting to pull the moon apart in places that are competing with these forces that are acting to shrink the moon. And there's a couple of possibilities. One intriguing one is the possibility that these areas that are being - are actually being picked up and kind of stretched because magma is trying to rise below the surface.

It doesn't make it to the surface, but it's trying to rise below - to rise up and, again, as it does, it sort of lifts it up and cracks it and stretches it. The trouble with that model is, though, that we don't see any evidence for really, really young volcanic material on the surface of the moon.

FLATOW: Yeah.

WATTERS: But the - yeah. It's really interesting how young these features appear to be.

FLATOW: So you - do you think that there some day might be a volcano that we might discover or one that will actually spouts out, and it's easy to see from your orbiting stuff?

WATTERS: I would not say no, but I also wouldn't make any bets...

(SOUNDBITE OF LAUGHTER)

WATTERS: ...that that's likely to happen.

FLATOW: That's called hedging your bets.

(SOUNDBITE OF LAUGHTER)

WATTERS: Right.

FLATOW: But it should be. But if you're saying - what you're saying, if I hear you correctly - now I'll put words in your mouth - is that if there is molten lava under the moon, it should spout out someplace.

WATTERS: Well, it's possible.

FLATOW: It's possible.

WATTERS: It all depends on the conditions. I mean, there are, again, other possibilities for how these stretch marks, as you described them...

FLATOW: Yeah.

WATTERS: ...may have formed on the moon. And another possibility is that they are connected with the fact that the moon is actually contracting. And what happens - at least theoretically - as the moon is contracting, blocks of the crust may actually be bent and flexed as part of that contractional process. But we still have a lot of work to understand this. Again, some of my colleagues are not particularly thrilled with the idea of young volcanism on the moon. But, again, one of the things that's really fascinating about these features are their youth. I mean, we have looked at these contractional faults scarps, and we knew that they were younger than a billion years, and we knew that they were likely much younger than a billion years. Maybe hundreds of millions of years old, maybe even tens of millions of years old, but we couldn't be sure.

One thing that's really interesting about these very, very small, narrow graben features as we call them is that they won't survive long at all on the moon because they're just very shallow. And the moon is an active place in terms of micrometeorite bombardments, and soil gets picked up and deposited, and so very small, very shallow-depth trenches will actually be filled in. And we know this from looking at boulder tracks, of all things, boulders that have rolled down.

There's a greater paper that was done in the mid '70s where an analysis of boulders that have rolled off a hill near the Apollo 17 site created a track. One of them had a track, another one didn't have a track. And by dating the age of the boulders, the - we could actually date how long that boulder had been sitting there. We knew when it rolled down the hill; we could determine how quickly these trenches would fill in. So that's really exciting because it gave us another way to date these that we couldn't use to date these contractional fault scarps.

So we know these trenches can't be any more than 50 million years old, but that is so recent in geologic terms, Ira, that these things could be not only just 50 million years old, they could be 10, they could be one million years old. They could have been active 40 years ago, and that's the other intriguing possibility, is you have...

FLATOW: I'm hearing the science fiction music coming up.

(SOUNDBITE OF LAUGHTER)

WATTERS: Well, we had the great Apollo seismic network that was on the moon put up by the Apollo astronauts and operated for a number of years collecting data on seismic activity in the moon, and the moon was active seismically very deep. But there is also a small number of moonquakes that occurred within the crust of the moon, and it's not impossible that those moonquakes are connected to these very, very young tectonic features.

FLATOW: So they could be really young...

WATTERS: Yes.

FLATOW: ...I mean, 40 years ago.

WATTERS: Yes.

FLATOW: Wow. And men were on the moon when they were happening.

(SOUNDBITE OF LAUGHTER)

WATTERS: And could be.

FLATOW: Does the moon have plates, tectonic plates like we have, on the moon?

WATTERS: No. The moon is in the - well, let's put it this way. The Earth is really unique among the terrestrial planets in that it has this mosaic of plates that shift and collide into one another, shift past one another. And again, most of the tectonic activity and volcanic activity on the Earth is concentrated at these plate boundaries. The moon is like a one-plate object. The moon, Mercury, other planets in the solar system appear to be one-plate objects. So when they contract globally, it's acting on a single plate.

FLATOW: Yeah. So the other question being, if the astronauts were on the moon, why did they not see any of these stretch marks on their side of their moon? And you haven't found it on the bright side, so to speak, that's facing us.

WATTERS: Well, there actually are some on the near side, but you're right. Some of the most exciting - actually the most exciting example that we found is on the far side. It's almost exactly on the opposite side of the moon that faces the Earth. And it may, again, be that there are just subtle forces that are acting within the moon that are creating just enough force to create these graben. It's also interesting because it tells us something about the stress state of the moon very recently, and that helps us figure out how the moon evolved and maybe even how the moon formed.

FLATOW: But you're not giving up - that doesn't bash the idea that the Earth was hit by another body and smashed the moon off as a piece?

WATTERS: No. No.

FLATOW: That's still the active - that doesn't do anything to that theory.

WATTERS: No. This actually picks up when all that is over, and the moon has actually coalesced and formed. And it's the sort of the history of the moon from that point on, that these kind of observations could very helpful in determining, again, the moon's evolution.

FLATOW: You know what you're doing. You're making the moon more interesting, which is dangerous, I think.

(SOUNDBITE OF LAUGHTER)

FLATOW: It's that people want to go back and study this stuff that we never thought we'd have to wonder about it, right, you know?

WATTERS: Well, that's true. I mean, I - one thing I want to mention is just - and it's very exciting - again, this is one of the exciting things about being a planetary scientist. Right now, we have imaged less than half of the moon with this very, very high-resolution images coming back from the Lunar Reconnaissance Orbiter. So we have, again, literally, more than half the moon to image with these, again, very high-resolution images, and we're very excited about the idea of finding more tectonic features, more features - more surprises. And that's really one of the exciting things about exploration.

FLATOW: Yeah, it is. And how long will it take to finish the job here, all those photos?

WATTERS: To do the job completely, we may need about four more years, an extended mission. It takes quite awhile. So we've been in orbit since 2009, and here we are, 2012, and we're still collecting data. So quite a while, and we're hoping to have an extended mission that will allow us to do that.

FLATOW: You mean like the little Mars rovers, keep - just keep going with your mission.

WATTERS: Yes. Well, we're very fortunate. The Lunar Reconnaissance Orbiter spacecraft is extremely healthy. We're in a very stable orbit. We could easily operate for four more years.

FLATOW: Do you have the budget for that?

WATTERS: Well, that's a question I can't answer...

(SOUNDBITE OF LAUGHTER)

FLATOW: As they say in Washington, that's above your pay grade, correct?

WATTERS: Exactly. You took the words right out of my mouth.

(SOUNDBITE OF LAUGHTER)

FLATOW: Well, you can always hope, you know. Look what - you can point to the success and the Mars rovers and things just keep going and finish the rest of the moon.

WATTERS: Well, when you think about it, too, it's a great investment. We've got - it's a relatively small amount of money compared to what it would cost to rebuild a spacecraft like the Lunar Reconnaissance Orbiter and put it in lunar orbit.

FLATOW: Well, you know what's on your side is exploring the moon has already been thrown into the presidential race, in a different context, but we might have some other ideas here.

WATTERS: Yes, it's possible. One of the interesting connections was the idea of whether a moon base would actually survive now based on these new findings. And I think I can safely tell you that the moon base would not be in great jeopardy unless you actually built it on a fault surface.

FLATOW: All right. Tom, that's quite fascinating. Thank you very much for taking time to be with us today.

WATTERS: My pleasure.

FLATOW: Tom Watters, senior scientists at the Center for Earth and Planetary Studies at the Smithsonian National Air and Space Museum in Washington. This is SCIENCE FRIDAY from NPR.

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