Scientists don't know what the early moon looked like. But new images from NASA'S Lunar Reconnaissance Orbiter, published online today in Science, might offer a clue. The spacecraft discovered 14 tiny thrust faults a few kilometers long, the kind of faults that usually appear wherever tectonic plates—or entire planets—compress. Researchers say the faults probably formed less than a billion years ago as the moon contracted and cooled from its fiery beginnings. But the fact that the faults are so small—not nearly as long as the hundred-kilometer ones on, say, Mercury—suggests that the moon hasn't had to cool that much to reach its present state. And that means the early moon probably wasn't a molten glob, as some researchers suspected. Instead, it may have been covered by an ocean of magma around a cooler core.
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