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The lunar mantle – the geological layer between the superficial crust and the central core – could include the low calcium pyroxene and olivine minerals, as suggested by the Chinese Lunar Mission Chang'E-4.
In January 2019, the Chang'E-4 lander successfully landed on the hidden side of the moon, inside the largest impact crater on the satellite, known as Von Kármán. He then deployed a mobile, Yutu-2, to sample and analyze the bottom of the crater.
In an article published in the journal NOTnature, researchers led by Chunlai Li of the Beijing Chinese Academy of Sciences delivered the first installment of results.
The choice of the crater as the landing point for the mission was motivated by the essentially geophysical nature of the Chang'E-4 project. The scientists responsible for the mission are resolved to solve a long-standing mystery about the composition of the lunar mantle.
It is thought that the general mechanics of how the moon has formed around its dense iron core is well understood and not controversial.
At an advanced stage of moon formation, the energy of incoming meteorites caused the warming of its outer layers and their transformation into a magical ocean. The liquid gradually separates with a relatively light mineral, a member of the feldspar group called plagioclase, which floats on the surface.
Plagioclase remains the dominant component of the crust.
Meanwhile, iron-rich minerals in the magma-gloop flowed. Finally, the ocean has cooled and solidified, stabilizing both the dense mantle and the lighter upper layer.
In the absence of a very large rig, determining the exact composition of the mantle is a challenge for lunar geophysicists.
Previously obtained information from spacecraft in orbit indicated the presence of fragmental materials rich in iron and magnesium, scattered on the surface in some areas, and identified them with pyroxene – a class of minerals including jade – and at the same time. olivine, common on Earth, greenish color and sometimes known as peridot gemstone.
It has not been possible to definitively determine the provenance of their mantle, leaving open the possibility that they may be exogenous – perhaps debris from a meteor strike.
However, scientists working on the Chinese project felt that an incoming meteor large enough to create a massive crater might have had enough momentum to break through the crust and get into the mantle – by projecting fragments on the surface.
Hence the choice of Von Kármán.
Li and his colleagues report that the observations made by the onboard instrument of the visible and near-infrared spectrometer (VNIS) of the rover indicate the presence of the same two key minerals.
Further research will be needed to absolutely confirm their underground origin. However, researchers suggest that although they are components of the mantle, they do not come from the Von Kármán crater.
They rather suggest that they were probably ejected as a result of the impact that caused a nearby hole – the 72-mile wide Finsen crater – and were propelled into the air up to their height. last place of rest.
In a related editorial of the same issue of NaturePatrick Pinet of the Institute for Research in Astrophysics and Planetology (IRAP) in France describes the Chinese results as "exciting".
The results, he writes, "could have considerable implications for the characterization of the composition of the upper mantle of the Moon and for the establishment of constraints on the characteristics of the ocean of lunar magma that have varied over time".
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