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Gas Eruptions Likely Formed "New" Moon Features, Study Says

Kimberly Johnson
for National Geographic News
November 8, 2006
 
Did the moon just break wind?

Unusually "fresh" features on the lunar surface appear to have been created when gas trapped inside the moon erupted through deep-seated fractures, a new study suggests.

The gas likely burst forth as little as one million to ten million years ago.

That would make the features relatively young, since any time less than ten million years ago is "like yesterday" in comparison to the moon's age, said Peter H. Schultz, a planetary geologist at Brown University in Providence, Rhode Island, and lead study author.

The finding could prove that the moon is still an active body, countering the long-standing belief that there has been no major lunar volcanism in the past three billion years.

Reporting in tomorrow's issue of the journal Nature, Schultz and colleagues suggest that such outgassing could be responsible for the formation of four to ten similar sites on the moon—and could still be occurring today.

Colorful Revelation

Scientists have suspected that the moon's D-shaped Ina structure is unique ever since Apollo 15 astronauts took images of the feature while flying overhead in 1971.

(Related photos: the final Apollo mission.)

Because the moon has no atmosphere, space debris easily reaches the surface and continuously forms impact craters—the primary type of new lunar surface features.

"Impacts have ruled the day for anything new on the moon," Schultz said.

But images of the 3.8-square-mile (10-square-kilometer) Ina site show few craters inside the structure and features still sharp with little erosion.

So Schultz's team analyzed crude spectral data images of Ina and compared them to images of newly formed craters.

Light reflects differently off lunar dirt that has been recently disturbed, so images that capture spectral signatures can show when and where changes on the moon's surface occur.

The color distinctions of the Ina structure show that the area is fresh compared to other sites, Schultz says.

Like a nearby crater to the west, Ina's floor is covered with titanium-rich basalt, which has a blue spectral color. The region is also peppered with green, the color that marks less mature dirt.

"Most [moon] craters are degraded," Schultz added. "These [Ina features] are not degraded. It's a surface that has been recently formed or exposed."

Scientists say that gas buried deep inside the moon's interior likely erupted, causing a "poof" of air to disrupt dirt on the surface.

The force probably blew the dirt straight up and it either came right back down or fell to the side, says University of Hawaii lunar expert Jeff Taylor, who was not involved in the research.

Such poofs of erupting gas might be the only source of wind on the moon's surface, he adds.

"It's like a steam eruption, but with no water vapor."

Which Gas?

Exactly what kind of gas might be erupting remains a mystery.

Scientists have found traces of radon near Ina, but study co-author Schultz thinks the main culprit could be carbon monoxide.

Hydrogen is also believed to be present at the lunar poles in the dust and ice, so it too could be the gas in question.

The mystery, Schultz said, "may hold clues for the formation of the moon and even the early history of the Earth."

Both Schultz and Taylor say it's unclear just how these findings will affect NASA's lunar exploration program, which includes plans to resume moon landings by 2018.

The presence of gas-formed structures "won't direct a new mission," Schultz said.

"But such features will clearly be targets of interest to see how often the moon burps and what deposits may have been left."

The University of Hawaii's Taylor said: "I think the biggest thing is that [this study] says the moon is not quite the dead object that many people think."

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