In research published in the journal Nature on May 16, scientists from the Chinese Academy of Science's national astronomical observatories reveal the lunar surface of the South Pole-Aitken Basin is slightly different from what they expected.
A core theory assumes that the moon was not as cold and dead as it is today. Instead, it probably began as a giant, melted marble full of magma oceans. These oceans were gradually cooled, the deposition of heavy minerals such as the green olivine or the low calcium pyroxes deeper into the lunar mantle. Less dense minerals flow to the top, thereby giving the moon a series of obvious geological layers as a cosmic onion. The crust, the uppermost layer, consists mainly of aluminum silicate or plagioclase.
"Understanding the composition of the lunar mantle is critical to testing if a magma sea ever existed, which postulated," co-author Li Chunlai said in a press release. "It also helps to deepen our understanding of the moon's thermal and magmatic development."
Understanding of the mantle composition gives planetary scientists more insight into how interiors from other planetary bodies – including the earth – can evolve.
Chang 4 landers originally landed in the Von Kármán crater, located on the floor of the South Pole-Aitken basin, back in January. The lander then sent a rover, Yutu-2, equipped with a spectrometer that measures reflected light. By studying the light reflected from the surface that the rover rolled along Von Kármán, the researchers were able to discover minerals and determine their chemical composition. Instead of seeing much plagioclase, the rover discovered a dominance of olivine and pyroxene.
Since these elements are expected to be much deeper in the mantle, the authors suggest that they be ejected from a stroke event caused by a meteor striking the moon surface. The rover explores nearly 72 kilometers of the Finnish crater, so the minerals may have been sprayed over the surface during that crater's creation.
Although NASA's Apollo mission landed people on the moon and Russia made a joint effort to retrieve lunar samples in the 1970s, no study of the lunar mantle had previously occurred. This makes China's mission particularly important, but due to the complexity of studying moon minerals on a planetary body hundreds of thousands of miles away, additional work will be required to gather a more complete understanding of the mantle's composition.