WASHINGTON - The moon's geological history is more complex than previously thought, preliminary results from China's first lunar rover, Yutu, suggested Thursday.

Ground-penetrating radar measurements taken by Yutu, also known as Jade Rabbit, revealed at least nine subsurface layers beneath its landing site, indicating that multiple geologic processes have taken place there.

"We have for the first time detected multiple subsurface layers (on the moon)," said lead author Xiao Long, professor of the China University of Geosciences in Wuhan, attributing these layers to ancient lava flows and the weathering of rocks and boulders into regolith, or loose layers of dust, over the past 3.3 billion years or so.

One of the most interesting findings is a layer at depths of 140 meters to 240 meters, said Xiao, who is also professor of Macao University of Science and Technology.

"We think this layer is probably pyroclastic rocks which formed during the course of volcanic eruptions," Xiao told Xinhua via email. "It reveals the diversity of volcanic activity, but what's more important is that it shows there are plenty of volatile contents inside the moon."

Yutu is part of China's Chang'e-3 moon mission, which delivered the rover and a stationary lander to the lunar surface on Dec. 14, 2013, marking the first moon landing since the Soviet Union's Luna 24 mission in 1976.

It touched down on the northern Mare Imbrium, also called Sea of Rains, a region not directly sampled before and far from the US Apollo and Luna landings sites.

Yutu traveled a total of 114 meters following a zigzagging route, then came to a halt about 20 meters to the southwest of the landing site due to mechanical problems.

So the rover just surveyed a small area using two radar antennas capable of penetrating the Moon's crust to depths of about 400 meters.

The data, however, were enough to show its landing site is compositionally distinct from previous Moon-landing sites, the researchers said.

"Overall, we have already had a general scientific understanding of the moon thanks to these lunar missions," Xiao said. "But if we want to have a comprehensive understanding of moon's geological structure, material composition and formation, as well as its evolution, a large number of exploration events are still needed. Meanwhile, effective international cooperation is a must considering the high cost of these activities."

The findings were published in the US journal Science.