Water found in moon matter counters the long-held belief that Earth's satellite is bone dry, researchers announced today.
Geologists used new technology to coax water molecules from volcanic glasses brought back decades ago by two Apollo missions.
The researchers believe the water was ejected along with magma when "fire fountains" erupted more than three billion years ago from the moon's surface.
The finding raises new questions about the long-standing "giant impact" theory, which holds that the moon was formed more than a billion years prior to that when a Mars-sized body slammed into Earth and sent debris into orbit.
(Related: "Moon Facts" [July 14, 2004])
Researchers once believed the impact was hot enough and long enough to vaporize volatile elements, including the building blocks of water.
The new study "puts some limits on how hot this planet was and how quickly the volatile elements condensed back into the solid," said study lead author Alberto Saal, a geologist at Brown University.
"What is important for me is it's telling me something about the origin of the moon and the Earth and the presence of water at very early times," he said.
The study appears in the July 10 issue of the journal Nature.
Not So Hot
Most astronomers believe a rogue planet collided with Earth about 4.5 billion years ago. The impact sent molten debris into orbit around Earth, some of which coalesced to form the moon.
Under this scenario, the heat of the impact should have vaporized light elements, including the hydrogen necessary for water to form.
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