China’s Chang’e-4 mission to the dark side of the moon has discovered signs of mantle material at the moon’s surface, “effectively setting an ‘X’ on lunar maps for future explorers seeking this not-so-buried geological treasure,” reports Scientific American. From the report: China’s Chang’e-4 mission touched down near the south pole on the lunar far side on January 3, 2019, the first spacecraft ever to land intact on this largely unexplored region of the moon. Consisting of a lander and rover, the mission is still going strong today, with the rover — called Yutu-2 — continuing its journey across the surface. On board are a variety of instruments, and today in Nature scientists from the Chinese Academy of Sciences in Beijing report the mission’s first scientific results, suggesting lunar mantle material has at last been located. “We found that the material of the Chang’e-4 landing site is mainly composed of olivine and low-calcium pyroxene,” says Dawei Liu, one of the paper’s co-authors. “This mineral combination is the candidate mantle-derived material.” Chang’e-4 rests inside the South Pole-Aitken (SPA) basin, which, at 2,500 kilometers across, is one of the solar system’s oldest and largest known impact craters. Specifically, the mission touched down in the 186-kilometer-wide Von Karman crater within this larger basin. Von Karman was produced billions of years ago by the impact of a large comet or asteroid; such collisions can excavate mantle material from deep underground, allowing it to be scattered across the surface by subsequent impacts. The mantle material was discovered using the Visible and Near Infrared Spectrometer on Yutu-2, which can ascertain the chemical composition of rocks by studying their reflected light. Both olivine and pyroxene are believed to be among the first minerals that froze out from the moon’s magma ocean as it cooled, falling to its solid base deeper in the mantle. Because previous surveys from orbit have revealed much of Von Karman’s floor to be composed of lava from volcanic eruptions rather than excavated mantle, the paper’s authors suspect the material detected by Yutu-2 was actually blasted into Von Karman from the upper mantle beneath another nearby impact structure, the 72-kilometer-wide Finsen crater.

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