Chinese lunar mission uncovers new mystery

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

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

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

It was possible now. Chinese scientists manually selected several small fragments of basalt (a volcanic rock), about 2 millimeters, for the research. Who showed effectively an eruption time of 1.97 billion years ago, a billion years younger than any previously dated lunar basalt lava.

A new mystery

Numerous volcanic eruptions have occurred on the moon’s surface during its geological history, forming large layers of basalt rock. These can be seen as dark spots on the moon. But most of the volcanic activity took place between 3 and 4 billion years ago. Planetologists have confirmed this by dating basalts from the Apollo and Luna stone collections, as well as meteorites from the moon. Until now, however, the younger volcanic rocks predicted by crater count studies had remained elusive.

For volcanic eruptions to occur, heat is needed inside a planet to generate molten material. For a planet the size of a moon, this heat would have been lost long before these eruptions 2 billion years ago.

Some theories

So the question now is how a small rocky planetary body like the moon could retain enough internal heat to continue to produce volcanic eruptions 2.5 billion years after its formation 4.5 billion years ago.

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

It remains to be seen if what is called tidal heating could have played a role, where heat was generated inside the moon due to the gravitational pull between the moon, the earth and the sun. .

Another explanation is that a unique aspect of the composition of the lunar mantle may have resulted in a lower melting temperature, which is how the molten material formed.

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