The story of China's Yutu lunar rover has been a rollercoaster from the start. The plucky mobile robot was delivered to the Moon by the Chang'e 3 spacecraft on December 14, 2013, achieving the first soft lunar landing since the Soviet Luna 24 lander touched down in 1976.
But about a month after it had rolled out onto the Mare Imbrium territory, the Yutu rover experienced an electrical short that rendered it unable to prepare for the harsh lunar night. With its instruments unprotected from the punishing cold and communications apparently lost, the Yutu was declared dead on February 12, 2014.
To twist the knife, whoever is behind the mission's unofficial Weibo account (which is the Chinese equivalent of Twitter) posted a series of pathos-filled reflections about life from the perspective of the Yutu rover, including this tear-jerker:
"The sun has fallen, and the temperature is dropping so quickly…to tell you all a secret, I don't feel that sad. I was just in my own adventure story—and like every hero, I encountered a small problem."
"Goodnight, Earth," it concluded. "Goodnight, humanity."
Despite these heartfelt messages to its followers, it turned out that the Yutu rover wasn't down for the count just yet. On February 13, 2014, the China National Space Administration (CNSA) announced that the Yutu was communicating again, though it still couldn't power down for lunar nights properly, and thus had no power to explore any further than the 114 meters it had already roved.
Now, over a year later, the rover is still responsive to commands, having outlived its expected mission duration several times over. Though it is permanently immobile and experiences increasing instrumental damage with every passing lunar night, it still has a few useful functioning systems, including ground-penetrating radar.
In fact, this week the Yutu team published a paper in Science based on the data collected by the Yutu rover's radar sweeps, which penetrate about 400 meters (1,300 feet) into the ground. The results suggest that the Mare Imbrium's has had a tumultuous geological history, while also proving that even a troubled mission like Yutu can deliver important results.
"The Lunar Penetrating Radar detection and integrated geological interpretation have identified more than nine subsurface layers, suggesting that this region has experienced complex geological processes since the Imbrian and is compositionally distinct from the Apollo and Luna landing sites," wrote the authors in the paper's abstract.
According to lead author Long Xiao of the China University of Geosciences, this complex geological area was formed by repeated volcanic activity, which has filled the Mare Imbrium multiple times in the region's history. Layers of volcanically formed basalt and silicate crystals are mixed in among the dust of eroded boulders, forming a heterogeneous surface regolith.
"Two things are most interesting," Xiao told Space.com on Thursday. "One is [that] more volcanic events have been defined in the late volcanism history of the Moon."
"Another is the lunar mare [volcanic plain] area is not only composed of basaltic lavas, but also explosive eruption-formed pyroclastic rocks," he continued. "The latter finding may shed light on…the volatile contents in the lunar mantle."
Yutu's success in collecting valuable data about this unexplored and geologically unique region is a testament to the CNSA's ambition and perseverance. It's also a timely reminder of how complicated extraterrestrial exploration roving is, and how much can go wrong. Just this week, for example, the Mars Curiosity rover recovered from a short circuit, and ESA renewed its attempts to contact the lost Philae lander on Comet 67P.
Clearly, China's lunar rover is far from the only 21st century interplanetary explorer to have pulled through against the odds, and gone on to enrich our understanding of unexplored worlds. Perhaps this week, the Philae will follow its example and pipe up after its own sun-starved period of hibernation. Yutu is clear proof that crazier things have happened.