The volcanism that formed the few maria on the far side "lasted longer than previously considered and may have occurred episodically," the study says.
Pieters said, "The thermal history of the moon is certainly more complex than originally thought."
Craters as Clocks
Researchers have had easy visual access to the near side of the moon with Earth-based telescopes. The far side has been more difficult to observe.
KAGUYA, which was launched and began orbiting the moon in the fall of 2007, has sent back some of the first high-resolution images of the moon's dark side.
Using these images, the research team was able to manually count craters in several regions.
Michelle Kirchoff of the Lunar and Planetary Institute in Houston, Texas, who was not involved with the study, said crater counting is generally a reliable method for estimating the ages of lunar landscapes. "But without samples to constrain the calculations, they are just estimates."
Sampling lunar rocks "would be a great follow-up," Kirchoff said, "but this would require a whole other lunar mission and that's something that may not occur for a while."
More results will arrive soon to help solve to the lunar puzzle.
Brown University's Pieters pointed out that Japan, China, and India all have modern instruments orbiting the moon, and the United States will launch the Lunar Reconnaissance Orbiter next April.
(Read more about moon exploration.)
"After a great data famine," Pieters said, "this feast of quality new information about the moon will open a renaissance of scientific exploration and new understanding of Earth's nearest neighbor."
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