STEVE INSKEEP, host:
Well, an old saying tells us that there's nothing new under the sun. But there is now something new that we have learned about the moon. The moon looks like a dead junk of rock, but scientists argue in today's issue of the journal Nature that, geologically speaking, it is alive. Researchers say the moon recently belched up a violent burst of gas from deep underground, and they can see evidence of that on the surface today.
Here's NPR's Richard Harris.
RICHARD HARRIS: The curious feature on the moon's surface looks like a D-shaped dent, as if a giant stomped down with his boot heel. It's a couple of miles wide and about 60 feet deep. Peter Schultz at Brown University says the so-called Ina(ph) structure was discovered by the Apollo missions to the moon.
Professor PETER SCHULTZ (Professor of Geological Studies, Brown University): Astronauts noticed this when they were going around, and it was very distinctive. After going over this gray-brown real estate, they would suddenly see this thing that looked much fresher and bluer. It's always been a mystery.
HARRIS: Schultz is a geologist and an astronomer, and he's been puzzling over this himself for many years. Now he has pulled together information from Apollo and more recent missions to figure out what could have caused it. One thing seems evident: It wasn't created by bombardment from outer space the way most of the moon's features are.
Prof. SCHULTZ: It just came from within. Very likely there was gas that found its way up through the cracks and crevices of the moon and then was released. And we're speculating that it was probably sudden. Because it has to be sudden enough to keep the lunar surface freshened to the point where it looks like it was formed yesterday.
HARRIS: And Schultz really does mean there could have been out-gassing there extremely recently, in geologic terms.
Prof. SCHULTZ: We don't know if it burped yesterday, or it burped a million years ago, or two million years ago. What we do know is that it's burping long enough and often enough to keep the surface from becoming impact battered, as you normally see the rest of the moon.
HARRIS: The big question now is what could have triggered this lunar burp. After all, the geology of the moon suggests that most volcanic activity ended there three billion years ago. And since then it seemed mostly a punching bag for meteors and stray asteroids. Shultz says that's not what the new finding is telling us.
Prof. SCHULTZ: I think it's telling us that the moon hasn't stopped what it's doing from the inside. It's not just a body that's a target for impacts from outer space. It also has stuff going on from the interior.
HARRIS: He speculates that pockets of gas could occasionally be jarred free by lunar quakes, which the Apollo mission also discovered. Another idea.
Prof. SCHULTZ: It could be there's still cooling down there. And occasionally as magmas begin to solidify it releases things that don't go into the minerals, and they escape along cracks and occasionally bursts out.
HARRIS: This is exciting news to folks who study the moon, like Paul Spudis at the Johns Hopkins Applied Physics Laboratory. He says the notion that the moon is actively producing gas raises some intriguing possibilities.
Professor PAUL SPUDIS (Applied Physics Laboratory, Johns Hopkins): If you found a site where gas was actually being released, you might actually be able to collect that material and possibly use it.
HARRIS: That depends, of course, on what the gas actually is.
Prof. SPUDIS: Natural radon may be present, but the typical thought is that it's associated with other things, things like carbon monoxide.
HARRIS: Carbon monoxide and radon gas, it doesn't exactly sound like a picnic.
Prof. SPUDIS: It doesn't, but at the same time it might be useful in a variety of different processes. So if you actually people living on the moon, they may be able to find a use for it.
HARRIS: Naturally, the first step is to get a closer look at this area and similar features that are scattered here and there on the lunar surface. And after many years of neglect, Peter Schultz says the moon will soon be the focus of a new wave of exploration.
Prof. SCHULTZ: Stay tuned, because I don't think the story is done yet. I think there's going to be a lot more big surprises in store for us from the moon.
HARRIS: Richard Harris, NPR News.
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