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The Chinese lander Chang'E-4 has recently landed at Von Karman – a 180 km wide crater located in an even larger impact crater known as the South Pole-Aitken Basin – and has deployed its Yutu Rover. 2. The rover has now found material derived from the mantle on the floor of Von Karman's crater.
This image captured by the Chang'E 4 lander shows the landscape near the landing site. Image credit: NAOC / CNSA.
"A theory emerged in the 1970s that as early as the moon's childhood, an ocean of magma covered its surface," said Professor Chunlai Li, a researcher at the National Astronomical Observatory of Japan. Chinese Academy of Sciences and colleagues.
"As the molten ocean began to cool down and cool down, lighter minerals floated upward, while heavier components sank. The top is covered with a layer of mare basalt covering a coat of dense minerals, such as olivine and pyroxene. "
"When the asteroids and space debris crashed to the surface of the moon, they split through the crust and threw pieces of the lunar mantle."
"Understanding the composition of the lunar mantle is essential to verify whether an ocean of magma has ever existed, as supposed. It also helps us to better understand the thermal and magmatic evolution of the Moon. "
On January 3, 2019, Chang'E-4 safely landed on the ground of Von Karman's crater and released the Yutu-2 mobile vehicle.
New measurements of the Yutu-2 visible and near infrared spectrometer suggest the presence of two lunar mantle minerals – pyroxene and olivine – at the site.
The Yutu-2 rover moves on the other side of the Moon. Image credit: CNSA.
"Yutu-2 collected spectral data on the flat expanses of the basin, as well as other smaller but deeper impact craters in the basin," the scientists said.
"We were expecting to find a wealth of mantle materials excavated on the flat soil of the South Pole-Aitken Basin, as the original impact would have penetrated well into and beyond the lunar crust."
"Instead, we found only traces of olivine, the main component of the Earth's upper mantle."
"The absence of abundant olivine in the interior of the South-Aitken Pole remains an enigma. Could the predictions of a lunar mantle rich in olivine be incorrect?
"Not enough, it turns out that more olivine appeared in the samples as a result of deeper impacts.One theory is that the mantle is made up of equal parts of olivine and pyroxene, rather that to be dominated by one on the other. "
"Yutu-2 will have to explore further to better understand the geology of its landing site, as well as collect much more spectral data to validate its initial results and fully understand the composition of the lunar mantle."
The results appear in the log Nature.
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Chunlai Li et al. 2019. Initial spectroscopic identification of Chang'E-4 of materials derived from the mantle of the lunar posterior surface. Nature 569: 378-382; doi: 10.1038 / s41586-019-1189-0
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