October 26, 2021

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China's moon mission reveals new mystery

China’s moon mission reveals new mystery

1.97 billion years ago, lava was still flowing on the moon’s surface. This is evident from the stones returned by the Chinese Chang’e-5 lunar expedition. But this creates a new mystery: The Moon must have been cold for two billion years by then. What explains later volcanic activity than expected? For now, this is a mystery.

Chang’e-5 was an unmanned mission that landed on the near side of the moon (the side facing Earth) in December 2020. The mission returned 1.7 kilograms of moon rock – the first samples collected from the moon since the Soviet Union’s Luna 24 mission in 1976 .

One of the goals of the Chang’e-5 mission was to find evidence of some of the moon’s recent volcanic eruptions. While scientists were previously able to predict igneous rocks of this age on the moon by studying the number of impact craters on the moon’s surface, it was impossible to confirm them without requiring samples to examine them.

It is now possible. Chinese scientists manually selected several small fragments of basalt (a volcanic rock), about 2 millimeters in size, for research. that showed Its eruption time was actually 1.97 billion years, a billion years younger than any previous basaltic lava from the Moon.

new puzzle

Numerous volcanic eruptions have occurred on the Moon’s surface during its geological history, forming large layers of basalt rock. These can be considered dark spots on the moon. But most of the volcanic activity occurred between 3 and 4 billion years ago. Planetary scientists confirmed this by dating basalts from the Apollo and Luna stone groups, as well as meteorites from the Moon. So far, however, the smaller igneous rocks predicted by crater census studies have remained elusive.

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For volcanic eruptions to occur, heat inside a planet is needed to generate magma. For a planet the size of the Moon, this heat is thought to have been lost long before volcanic eruptions two billion years ago.

some theories

So the question now is how a small, rocky planetary body like the Moon can retain enough internal heat to continue producing volcanic eruptions 2.5 billion years after it formed 4.5 billion years ago.

Although scientists have previously suggested that high concentrations of radioactive elements in the lunar interior could dissolve the lunar rocky material, the compositions of these samples indicate that this was not the driving force in this case.

It remains to be seen if so-called tidal heating played a role, as heat is generated in the moon’s interior as a result of the gravitational pull between the moon, Earth, and the sun.

Another explanation is that a unique aspect of the Moon’s mantle composition may have lowered the melting temperature, which explains how molten matter is formed.

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