What's the Latest Development?

New research has found that the moon's insides are likely as wet as the Earth's upper mantle, the region just below its miles-thick surface crust. The prevailing theory of the moon's formation holds that it coalesced from pieces of the early Earth blasted into space by a collision with a Mars-size object long ago. ... "You really would not expect, based on what we know about this model, to have any water present in the moon at all," said the study's lead author, Erik Hauri, of the Carnegie Institution of Washington. "The fact that these samples have terrestrial levels of water is really a stunner."

What's the Big Idea?

Researchers have long thought that the moon was created when a object collided with Earth during its formation, spilling matter into space that was then trapped in our planet's orbit. Scientists previously theorized that the amount of energy released during the moon's creation would have been enough to vaporize all its water. "At the moment, it's just difficult to account for the Earth-like levels of water—and chlorine, fluorine and sulfur—in the moon's interior," said the study's lead author, Erik Hauri, of the Carnegie Institution of Washington.