The first rover to visit the far side of the moon, China’s Yutu-2, has found stark differences between there and the near side. These include stickier, more supportive soil on the far side and a greater abundance of small rocks and impact craters.
Despite several exploratory missions to the moon, crewed and uncrewed, the moon’s far side has remained unexplored because of difficulties communicating with Earth from there. But in 2019, China’s Chang’e 4 mission deposited the Yutu-2 rover to roam the far side’s surface.
Now, Liang Ding at the Harbin Institute of Technology, China, and his colleagues have deduced something of the make-up and features of the far-side soil based on the way Yutu-2 has trundled around and on the observations it made using radar and spectrometry.
The researchers, who declined to be interviewed for this article, found that the rover didn’t slip and skid as much as it would have been expected to do on the moon’s near side, indicating that the far side was relatively flat. The soil also appeared to readily stick to the rover’s six wheels, which means it is probably more consolidated and supportive.
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As well as being useful for designing future lunar rovers, understanding the soil make-up and rock distribution can tell us about the history of the lunar surface itself.
“Finding a larger proportion of small rocks is probably linked with the age of the surface,” says Lionel Wilson at Lancaster University, UK. “You’ve worn down the larger rocks. If you wait long enough, you’ll reduce a rock just to several millimetre-sized particles.”
The Yutu-2 rover also found a dark greenish, glistening material at the bottom of one crater, similar to glassy materials found in Apollo mission samples. This is the first time that one of these minerals, probably a remnant of a previous impact, has been found in-situ on the moon.
“Any information on the history of bombardment, at all scales, from large impactors all the way down to the atomic scale, is really important and valuable,” says Wilson.
The lunar far side is also relatively electromagnetically quiet because it blocks out Earth’s transmissions, making it well suited for astronomy. Building any observatories there will require a deep knowledge of the soil make-up and surface of the lunar far side, which could be explored in future missions.
“The exploration of the far side is really in its infancy,” says Sara Russell at the Natural History Museum in London. “It’s like this whole new world to explore. We really have a lot to find out about the far side of the moon; it’s really exciting.”
Science Robotics DOI: 10.1126/scirobotics.abj6660
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