Researchers Discover Why Water Exists on the Moon

Water on moon likely produced by solar wind

The full moon sets behind the sculpture at the World War II memorial in downtown Moscow.
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When astronauts returned lunar rocks to Earth during the Apollo missions, scientists eventually found that some of the samples contained water. But they weren't sure about how the water got there — until now. And the discovery might mean Newt Gingrich's proposed "lunar colony" isn't as far fetched as it seems.

The water on the moon may have come, indirectly, from an unlikely source: the sun. Hydroxyl — a chemical group made up of a hydrogen and oxygen — is abundant on the moon. When hydroxyl interacts with the hydrogen in solar wind, which the sun emits constantly, it becomes water, according to Yang Liu, a scientist at the University of Tennessee-Knoxville. The process doesn't happen on Earth because of the planet's atmosphere.

But Liu's most important discovery is not how the water got there, she says, it's what humans might be able to do with solar wind and the moon's existing hydroxyl.

[PHOTOS: Constellation, NASA's Moon Program]

"There's a heated discussion about going back to the moon and trying to build a habitat," she says. "We might be able to use this process, not for drinking water, but for rocket fuels. It could be another energy source to power our space exploration and go beyond our solar system."

That's because water on the moon could potentially be converted to rocket fuel as liquid hydrogen or oxygen, she says. "It's not an easy process" to convert hydroxyl into rocket fuel, but Liu says it's feasible.

There could be as much as 3 metric tons of water on the moon, according to a "ballpark estimate" by Liu.

[READ: Did the Moon Sink the Titanic?]

The discovery also suggests that water could exist elsewhere in the solar system, including on Mercury and several asteroids.

"We have some tentative observations in terms of seeing ice in the polar region of Mercury," she says.

Mars, on the other hand, has an atmosphere. Any water on that planet was likely derived in another way, she says. "That's the big question we're trying to answer, why we're sending so many missions to Mars to address that question. Unless we have direct samples, we won't know."

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Jason Koebler is a science and technology reporter for U.S. News & World Report. You can follow him on Twitter or reach him at jkoebler@usnews.com.