The analysis of lunar rocks taken by the Chinese reveals the presence of lava on the Moon up to 2 billion years ago
The Chinese mission Chang’e-5 brought back to Earth, in December 2020, about two kilos of rocky material taken from the surface of the Moon.
The one fielded by China’s National Space Administration was the first mission to return lunar samples since 1976: the last was the Soviet Luna 24, which brought 170 grams of lunar soil back to Earth.
Scientists from all over the world have been busy these months studying the lunar rock samples, which seem to have much to tell us about the Moon, which has always been at the center of human imagination but still remains to be investigated in many ways.
The youngest lunar rocks ever
The Moon was formed about 4.5 billion years ago. Rock samples taken by the Apollo and Luna missions between the 1960s and 1970s seemed to point to a fairly accurate story: the Moon’s volcanic activity would have been exhausted in the first billion years of the satellite’s life, with adjustments that may have involved the next few million years.
Given the Moon’s size, scientists have always been fairly unanimous that the satellite began cooling about 3 billion years ago, to become “the quiet, inactive neighbor” of the Earth we know today.
The lack of craters in some areas, after all, would suggest the presence of volcanic activity well beyond the first billion years of the satellite’s life: in the absence of the lava hypothesis, it would not be easy to explain the Moon’s vast smooth surfaces.
On the other hand, a “small” object like the Moon should cool down much faster than the lunar samples collected by the Chinese seem to indicate.
The rocks taken from the Moon by Chang’e-5 are quite unique: they were formed about 2 billion years ago, making them “the most recent rocks ever taken from lunar soil,” says Carolyn Crow of the University of Colorado, one of the authors of the study. And it is from their analysis that “fiery” details emerge.
The Moon’s fiery “heart”
The lunar rock survey, research conducted by an international team and published in Science, suggests that the Moon has been volcanically active for much longer than would seem possible judging by its size.
Scientists involved in the study have therefore proposed several hypotheses, starting with the one that the most recent lava flows are the product of heat generated by the decay of radioactive elements.
It was precisely to verify the presence of such radioactivity of the lunar soil that the Chang’e-5 mission went to collect samples in an unexplored area of the satellite, the Oceanus Procellarum, which is believed to be of more recent formation.
Well, the chemical analysis confirmed the age of the rocks, no older than 2 billion years ago, but did not find the amount of radioactive charge sought to support the hypothesis. What has kept the Moon’s volcanic activity alive for so long, then? According to Alexander Nemchin, co-author of the research, one solution could be that gravitational forces from Earth liquefied the Moon’s interior, allowing magma to flow over its surface for a long time.
“The Moon was much closer to Earth 2 billion years ago,” explains Nemchin: the end of the Moon’s volcanic activity would then be the result of the gradual removal of the satellite from our planet, but that would not yet explain the presence of magma in the Oceanus Procellarum.
The research on the Moon is just beginning. Harald Hiesinger, of the University of Münster, has been studying the formation of craters on the surface of near-Earth celestial bodies for years, as analysis of impacts can reconstruct important fragments of the history of our solar system. The youngest-ever moon rocks, which arrived on Earth just a few months ago, have already revealed to scientists previously unimagined news and working hypotheses.