What happened to lunar volcanoes

An asteroid impact on the Moon started a fragment of the satellite surface and threw it into space. After a trip of thousands of years, the meteorite fell in northwest Africa, where it was discovered in February 2023. After two years of studies, it has helped cover a hole of one billion years in the lunar geological history.

Context. Apollo missions brought 382 kg of lunar rocks to Earth. The analysis of these rocks told us that the moon had had a violent volcanic past, but that its inner fire had turned off about 3,000 million years ago.

A much more recent mission, Chang’e 5, brought younger basalts, “barely” 2,000 million years. This still leaves us a huge hole of almost one billion years of lunar history in which we do not know what happened. Did volcanism go out and reactivated?

The answer came to us. And it has arrived, as so many times in science, by chance. A lunar rock found in the Norafricano desert in 2023 has turned out to be the piece that was missing in the puzzle. He NWA 16286 Meteorite Analysispresented at the Goldschmidt conference in Prague, suggests that lunar volcanism was a much more continuous process than we thought.

The lunar meteorite number 31. The protagonist of this story is a piece of soil of the moon of 311 grams, one of the only 31 lunar basalt meteorites officially identified on our planet. It was not brought by any astronaut or any probe, but reached the earth by its own foot. An asteroid impact on the moon started it from the satellite surface and threw it into space. After a trip of thousands of years, he fell in northwest Africa, where he was discovered in February 2023.

Studying the rocks that the moon sends us for free is an incredibly valuable way to explore its geology, because the rocks of the sampling return missions are limited to the immediate areas of the places chosen for the moon landing. Lunar meteorites can be expelled from anywhere from the moon surface. There is a lot of serendipia in this sample.

The missing piece. But the true importance of NWA 16286 resides in his age. He Lead isotope analysis He has dated the rock in about 2,350 million years. This makes it the youngest lunar basaltic meteorite ever discovered, and places it within that mysterious hole of one billion years in lunar volcanic history.

The samples of NASA and Luna’s Apollo missions of the Soviet Union are between 3,100 and 4,000 million years. Those of the Chinese Chang’e-6 mission (from the hidden face of the moon) They are about 2,830 million years. Chinese mission shows Chang’e-5 (from the visible face of the moon) are about 2,030 million years. NWA 16286 is in the middle.

Volcanic activity did not stop. The characteristics of the meteorite suggest that Lunar volcanic activity continued Throughout that time: the moon was not geologically dead. It is a basalt rich in olivine with unusually high levels of potassium. In addition, its “fingerprint” lead isotopic pointed out that it was formed from a source in the lunar mantle with a very high proportion of uranium-plaomo.

Potassium and uranium are radioactive elements, as is the thorium. Its disintegration along eons generates a constant amount of heat. The theory, now reinforced by this rock, is that lunar mantle bags enriched in these elements acted as a residual heat engine that maintained parts of the interior of the moon hot enough to produce magma and feed volcanoes much after what was thought.

What part of the moon came from? NWA 16286 has a different lithology from any known meteorite. It is believed that it came from a lunar sea so far not sampled. Its texture suggests a two -stage cooling story: a slow, perhaps in a magma camera, followed by an eruption in a lava flow of several tens of meters thick.

This rock not only resolves an old mystery, but also serves as a guide. Analyzing their trajectory and composition will help scientists identify the crater of origin on the moon, marking a priority point of interest for future sampling return missions. And so is how a rock found in the desert is telling us where we have to go the next time we visit the moon.

Image | SM BELARDO et al.

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