The farside of the moon is a lunar layer cake. New data from China’s Chang’e-4 lander and Yutu-2 rover reveal alternating layers of coarse rock and fine soil down to a depth of 40 meters, suggesting a history of violent impacts, scientists report February 26 in Science Advances.
“We know much of the moon’s nearside” from the Soviet Lunokhod and American Apollo programs, but little about the farside, says lunar scientist Yan Su of the Chinese Academy of Sciences in Beijing. “The Chang’e-4 mission revealed the first ‘ground-truth’ detailed subsurface stratigraphy … on the farside of the moon.”
Chang’e-4 and Yutu-2 became the first spacecraft to land on the farside in January 2019, touching down inside the 186-kilometer-wide Von Kármán crater (SN: 1/3/19). As Yutu-2 explored the crater, which lies within the 2,500-kilometer-wide South Pole–Aitken basin, the rover sent radar pulses into the ground to probe the material beneath its wheels.
Lunar scientist Chunlai Li, also of the Chinese Academy of Sciences, and colleagues analyzed the 106-meter path that the rover took in its first two lunar days (about two Earth months) of collecting data. The team discovered a layer about 12 meters thick of fine soil, or regolith, closest to the surface.
“It’s like being on very clean sand,” says study coauthor Elena Pettinelli of Roma Tre University in Italy. “It’s like you’re on the beach.”
Below that fine soil, the rover found another layer of about 12 meters containing coarser material embedded with larger rocks, like cherries in a fruitcake. And lower still was a series of alternating coarse and fine materials, spanning depths of about 24 meters down to roughly 40 meters — the limit of the rover’s radar.
