A Chinese lunar rover has discovered a new kind of rock on the surface of the moon, suggesting our cosmic companion has a more diverse makeup than previously thought, scientists say.
Traversing a dark basin on the lunar surface, the Yutu rover released from the Chang'e 3 robotic lander has detected evidence of a kind of basaltic rock not seen on the moon before, they say.
"We recognize a new type of lunar basalt with a distinctive mineral assemblage compared with the samples from Apollo and Luna, and the lunar meteorites," researchers report in their study appearing in Nature Communications.
The Chinese lander touched down on a comparatively young lava flow in the northern part of the moon's Imbrium basin, a large impact basin easily visible from Earth.
After the lava cooled around 3 billion years ago, another more recent impact in the basin exposed the ancient basaltic rock formed by the cooling lava. That more recent impact area has now been officially named the Zi Wei crater.
That allowed the Yutu rover to gather samples that scientists say give them a look deep into the moon's past.
The surprising chemistry of the samples, rich in titanium dioxide and also in the mineral olivine, suggests the basaltic rocks probably formed relatively late in the cooling process of the ocean of molten magma, the researchers say.
Scientists believe the moon was created when a cosmic body the size of Mars collided with the Earth, throwing off a largely molten body that, as it cooled, formed a crust, mantle and core, similar to the way the Earth evolved.
However, a buildup of heat from decaying radioactive elements in the lunar interior probably re-melted some of the mantle about 500 million years after the moon's formation, sending lava flowing over the surface and filling impact craters and basin like the Imbrium.
"The variable titanium distribution on the lunar surface suggests that the moon's interior was not homogenized," says researcher Bradley L. Jolliff, a professor of Earth and Planetary Sciences at Washington University in St. Louis who is part of an educational collaboration that helped analyze Chang'e-3 mission data.
"We're still trying to figure out exactly how this happened," he says. "Possibly there were big impacts during the magma ocean stage that disrupted the mantle's formation."
From 1969 to 1976, American Apollo missions and Russian Luna lander missions had sampled basalts from the moon's peak period of volcanic activity between 3 and 4 billion years ago, compared with the samples collected by the Chinese rover, which are 3 billion years old or perhaps slightly younger.
Other studies have suggested the existence of even younger or more diverse basalts on the moon, possibly waiting for future robotic missions or human explorers to discover, Jollif says.
