The Moon has gas
Eruptions confound the idea that our nearest neighbour is a geological dead zone.
Some think the Moon has been geologically dead for billions of years. But Peter Schultz of Brown University, Rhode Island, is not one of them. His results show that some lunar craters were formed as recently as 10 million years ago by gas eruptions, suggesting that there's still something bubbling away beneath the Moon's surface.
In terms of lunar geology, 10 million years is yesterday. It was thought that all volcanic activity stopped 3.2 billion years ago, and that any young craters were caused by meteor impacts. Time to think again, say Schultz and his colleagues in this week's Nature1.
Traces of radon, spotted by the Apollo mission in 1975, hinted that the Moon was still belching gas. The latest results can now tie those observations to features on the surface, says Paul Spudis, of the Lunar and Planetary Institute in Houston, Texas.
Those features are the craters at an area called Ina, a relic of volcanic activity. To find out how old these craters are, and what caused them, the researchers set about comparing them with better understood craters in other areas.
Ina has relatively few craters, which suggests it is quite young. This idea is supported by the presence of bright rubble in several of Ina's craters. Younger materials tend to show up as brighter, and observations suggest the craters contain recently exposed titanium basalt. This material is surrounded by a dark halo of older material, which is indicative of volcanic activity.
By comparing the interior rubble's brightness to nearby impact craters of known age, the researchers concluded that something other than an impact must have shifted the interior of Ina recently.
Together, the data have led Schultz to think that the craters must have been formed by volcanic activity gas eruptions no later than 10 million years ago. He suspects that things are still on the move: "We realize that there are still things happening on the inside." Spudis sees the finding as suggestive, rather than definitive.
Schultz is sure the work will encourage those scientists planning to return to the Moon, and help them to take the appropriate scientific instruments.
The gas is unlikely to make any difference to those thinking of colonization, Spudis says. "But you never know for long-term habitation, it may end up being important."
Lunar scientists will now be forced to rethink assumptions made about the Moon. "There is more to the Moon than we had previously discovered," says Schultz. "This shows there's still some life. We just have to learn how to take its pulse."
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- Schultz P. H., et al. Nature, 444 . 184 - 186 (2006).