Chang'E-4 initial spectroscopic identification of lunar far-side mantle-derived materials.

Abstract

Over 60 years of spacecraft exploration has revealed that the Earth's Moon is characterized by a lunar crust¹ dominated by the mineral plagioclase, overlying a more mafic (richer in iron and magnesium) mantle of uncertain composition. Both crust and mantle formed during the earliest stages of lunar evolution when late-stage accretional energy caused a molten rock (magma) ocean, flotation of the light plagioclase, sinking of the denser iron-rich minerals, such as olivine and pyroxene, and eventually solidification². Very large impact craters can potentially penetrate through the crust and sample the lunar mantle. The largest of these craters is the approximately 2,500-kilometre-diameter South Pole-Aitken (SPA) basin³ on the lunar far side. Evidence obtained from orbiting spacecraft shows that the floor of the SPA basin is rich in mafic minerals⁴, but their mantle origin is controversial and their in situ geologic settings are poorly known. China's Chang'E-4 lunar far-side lander recently touched down in the Von Kármán crater^5,6 to explore the floor of the huge SPA basin and deployed its rover, Yutu-2. Here we report on the initial spectral observations of the Visible and Near Infrared Spectrometer (VNIS)⁷ onboard Yutu-2, which we interpret to represent the presence of low-calcium (ortho)pyroxene and olivine, materials that may originate from the lunar mantle. Geological context⁶ suggests that these materials were excavated from below the SPA floor by the nearby 72-km-diameter Finsen impact crater event, and transported to the landing site. Continued exploration by Yutu-2 will target these materials on the floor of the Von Kármán crater to understand their geologic context, origin and abundance, and to assess the possibility of sample-return scenarios.