China's troubled lunar rover Yutu is still alive and functional after more than five months on the moon, a lunar program official said on Wednesday.

But its functionality has been weakened considerably by the bitterly cold lunar nights after the rover experienced a "mechanical control abnormality" in January, said Li Benzheng, deputy commander-in-chief of China's lunar exploration program.

The rover can still send data back to Earth via China's Chang'e-3 lunar probe, which carried Yutu to the moon, he said. But its wheels are no longer functioning, nor is the solar panel which should have been folded to provide thermal insulation during lunar nights.

"With each lunar night, the functionality of Yutu is weakened," Li said.

The rover, named after the pet of lunar goddess Chang'e in ancient Chinese mythology, touched down on the moon's surface on December 15, some hours after Chang'e-3 landed.

It was designed to roam the lunar surface for at least three months to survey the moon's geological structure and surface substances and look for natural resources.

But problems emerged before Yutu entered its second dormancy on the moon on January 25 as the lunar night fell. According to the State Administration of Science, Technology and Industry for National Defence, the mechanical abnormality occurred due to the "complicated lunar surface."

One night on the moon is about 14 days on Earth, during which the temperature falls below minus 180 degrees Celsius.

During the lunar night, there is no sunlight to power Yutu's solar panels. In this period, the rover is expected to stay in a power-off mode and communication with Earth is cut.

Experts had feared that it might never function again, but Yutu has so far managed to survive the bitter cold.

Li noted that the rover has already "over-served" its time on the moon.

"Yutu is really tough. We are really happy about that," he added.

(Xinhua News Agency May 28, 2014)