The ground-penetrating radar of a Chinese lunar rover found at least nine subsurface layers, evidence the moon has a more complex history than previously thought, scientists say.
The layers are hidden evidence of past lava flows and explosive eruptions, say researchers announcing their analysis of data from China's Yutu ("Jade Rabbit") lunar rover that landed on the moon in 2013.
The rover, released from the Chang'e-3 lunar lander, traversed part of the vast crater known as the Mare Imbrium, an area never sampled before.
The crater is thought to have formed about 3.8 million years by a large impact and subsequently filled with lava from eruptions.
"When you look at an image of this area, there are no features," says Long Xiao from China University of Geosciences in Wuhan. "But when we looked at the inside, there are many stories within it."
The scientists say they suspect the detected layering is the result of ancient lava flows alternating with layers of regolith, lunar soil formed as rock and boulders weather.
The complex subsurface structures suggest the northeast region of the Mare Imbrium basis is younger than the sites visited during NASA's Apollo moon landings from 1969 to 1972 and locations visited by Soviet-era moon landers, they report in the journal Science.
"There is more complex geological history than we had thought," they wrote, noting the rover's radar showed five distinct layers of lava in just the first 400 meters of the lunar surface.
More layers may exist even deeper, they said.
"It is very likely that more episodes of volcanic eruptions have filled the basin at greater depths," they suggested.
Some of those episodes may have been from explosive eruptions rather than the result of more gentle lava flows and filling, they suggested.
The third layer under the surface, at about 240 meters deep and around 3.3 billion years old, shows evidence of a texture similar to what happens on earth as violent eruptions spew large boulders known as pyroclastic rocks, they explain.
Earlier investigations by the Apollo landing missions and evidence gathered from lunar orbiters have only suggested evidence of more gently flowing basaltic lava, they said.
Explosive eruptions require the formation of lots of gas, and since the moon's surface rocks are mostly empty of chemicals that might have provided that gas, there is speculation volatile molecules - perhaps water - exist deep inside the moon's interior, the scientists proposed.
After being deployed in December of 2013, the Yutu rover traveled 374 feet over the lunar surface for one lunar day - 14 Earth days - before encountering a problem that stopped its ability to move.
"Unfortunately, Yutu encountered mechanical problems and has ended its mission," Xiao says. "No more data will come."
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