China’s Chang’e-4 mission to the far side of the Moon has detected minerals thought to have been excavated from deep beneath the lunar surface by an ancient asteroid.
The spacecraft landed in the Von Kármán crater in the South Pole-Aitken basin in January, marking the first time a probe has ever visited the Moon’s far side. In its first investigations, the mission’s Yutu-2 rover used a visible and near-infrared spectrometer to analyse the light reflected off the crater’s surface.
Characteristic absorption patterns in the light, described in a paper in Nature today1, suggest the presence of the dense minerals olivine and low-calcium pyroxene, which are unlike any samples returned by previous probes and might originate from the lunar mantle.
The authors say that the dense minerals might have been thrown out of the upper mantle during the impact event that created the basin. The material was likely scattered across the surface when another impact later created the nearby 72-kilometre-wide Finsen crater.
The findings lend weight to the theory that the Moon’s surface was once molten but separated into layers as it solidified, leaving largely lighter minerals in the surface crust and burying denser ones in its mantle.
Li, C. et al. Nature https://doi.org/10.1038/s41586-019-1189-0 (2019).