Soil On Moon’s Mysterious Far Side Is Similar To Earth’s Dry Sand, Reveals First Rover To Visit

Yutu-2 is the first rover to ever explore the far side of the Moon. Image Credit: CSNA/Siyu Zhang/Kevin M. Gill CC BY 2.0

In January 2019, China made history by landing the first-ever rover on the far side of the Moon. The Yutu-2 rover has been traversing the lesser-known side of the Moon for two years now, its exquisite suite of instruments delivering precious insights into the unexplored region. But it’s not just the scientific instruments digging up the dirt, so to speak. Even its wheels are carrying out science up there.

The rover was delivered by the Chang’e 4 lander (itself taking some breathtaking images and performing some pretty spectacular science, too) and has traveled more than 1,000 meters (3,300 feet) across the surface of the Moon. Now, reporting in Science Robotics, researchers have used the data captured from the rover's movements to establish properties of the lunar soil on the far side of the Moon.

The trek the rover has been on allowed them to establish how stable the terrain is and what kind of regolith – as soil on celestial bodies is called – it was dealing with. It appears to be quite different from what was experienced by the Apollo astronauts. In fact, it has some Earth-like qualities similar to dry sand.

“During its journey, Yutu-2 has experienced varying degrees of mild slip and skid, indicating that the terrain is relatively flat at large scales but scattered with local gentle slopes. Cloddy soil sticking on its wheels implies a greater cohesion of the lunar soil than encountered at other lunar landing sites,” the authors write in the paper. “Further identification results indicate that the regolith resembles dry sand and sandy loam on Earth in bearing properties, demonstrating greater bearing strength than that identified during the Apollo missions.”

The cause of this could be the greater period of space weathering. Another thing that looks different is the number of rocks and craters in the area, much greater than what has been observed on the near-side. In particular, fresh craters containing highly reflective material might be a consequence of secondary impacts – impacts created by lunar material thrown up into the (non-)air by a meteorite and landing back onto the surface.

The findings from Yutu-2 add to the wider scientific literature on the difference between the two faces of the Moon, the one we always see and the one hidden from us (unless you were one of the Apollo astronauts that got to fly over it).

Chang’e 4 landed on the Eastern floor of the Von Kármán crater, near the Moon's south pole. It is to date the first and only successful landing on the far side of the Moon.

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