THE MOON’S STICKY SOIL
The farside of the Moon is a far different place from the nearside. It has a more rugged surface, full of craters and missing the smooth, solidified-lava oceans on the Moon’s nearside. And it has a different composition, with fewer radioactive elements.
Now, you can add “stickier soil” to that list.
In a paper published Jan. 19 in Science Robotics, Chinese researchers gave an update on the Yutu-2 rover, which touched down on the Moon in 2019 with Chang’e 4, the first-ever mission to land on the lunar farside.
The team says that one of the most striking things Yutu-2 has encountered is how clumpy, or “cloddy,” the lunar soil has been. Images taken by the Chang’e 4 lander and the rover of its wheels show that much of its fine metal mesh is covered in dirt that it has picked up as it rolled across the lunar surface.
That might seem a small detail, but it’s scientifically intriguing: It stands in sharp contrast to the experience of Yutu-2’s predecessor, Yutu, which landed on the nearside in 2013. Though both rovers have nearly identical designs, the original Yutu never had any large clumps of dirt gather on its wheels in more than 2.5 years of exploration — only some fine dust stuck to the metal wheels thanks to static cling.
The difference is likely related to the conditions on the lunar farside: Because volcanic activity there ceased earlier than on the nearside, the farside surface is older than the nearside. And when lunar soil — called regolith — is exposed to the harsh conditions of space for millions of years, it absorbs repeated impacts from micrometeorites, a process called space weathering. These impacting particles don’t just pulverize the dirt into finer particles, they also melt them and fuse them into larger, irregular-shaped glassy globs, called agglutinates. Their irregular shapes can interlock with each other more easily, forming large clods.
Scientists should have a chance to look at the unique soil themselves in 2024, when Chang’e 6 is due to return the first-ever lunar farside samples.