At 2 billion years old, Chinese Chang’e samples are among the youngest moon rocks

The famous “Man on the Moon” is an optical illusion, based on patterns formed by the dark and white terrain of the Moon’s surface. The light-colored highlands are made up of anorthosite, an igneous rock believed to be the remnant of the moon’s primordial crust, dating from 4.5 to 3.9 billion years ago. Lunar marias, the dark regions of the moon, formed when the basins of the moon filled with basalt, a volcanic rock, about 3.9 to 3.2 billion years ago. There are no active volcanoes on the Moon that can be found today.

But the rock samples have returned to Earth recently The Chinese Chang’e-5 mission It turns out that the moon has been active much longer than previously thought. Chang’e-5 is the first mission to recover moon rocks on Earth in 45 years.

in a A study published in the journal Science, an international team of researchers discovered that basalt rocks collected by Chang’e-5 from a volcanic mound in The surroundings of storm Maria It is about 2 billion years old.

Jim Head, Research Professor in the Department of Earth, Environmental and Planetary Sciences at Brown University Co-author of the new study, he says, these samples fill critical gaps in scientists’ understanding of the moon’s history.

Previous samples from the Apollo missions and Soviet Luna missions all came from the central and eastern part of the near face of the moon. But remote sensing data indicates that the most recent volcanic activity on the Moon has occurred in the western part, so this area has become a prime target for sample collection.

Knowing the duration of lunar volcanoes is very important to understand the thermal evolution of the Moon. The Moon is much smaller than the Earth, losing its internal heat – leading to volcanoes on the surface – at a much faster rate. But the Moon may have held pockets of molten rock for much longer than previously thought, as Professor Head explains:

“The area from which these samples were sampled is a single area on the Moon, which appears to have high concentrations of radioactive elements – especially thorium. So an idea of ​​why the volcanic activity lasts longer in this area compared to others was that you have all of these radioactive elements concentrated together, which produces a lot of heat. This heat melts the mantle and causes volcanic flows.

“However, in these samples, we didn’t really see a high composition of radioactive elements. If these radioactive elements are the source of volcanic activity in this area, we would expect to see increased radioactivity in the samples. But we couldn’t. Instead of that. , the composition was similar to the Persian basalt of ancient sediments. This casts doubt on this hypothesis of long-term volcanism. ”

According to Professor Head, the new calendar is also important for further exploration of the solar system:

“When we look at a surface or feature on the Moon for which we don’t have radioactive dating samples, we try to estimate its age through the size and frequency distribution of the impact craters. Essentially, over time, the bigger the impacts get, so by calculating craters of different sizes, we can determine the relative age of the surface. But about one and three billion years ago, we didn’t not a lot of good data points to tell us what the effect of flow is. Having an absolute radioactive date for that surface seems to help us calibrate the flux curve, which helps us date other surfaces. This is not true. For the Moon only. It helps us calibrate the ages for Mars, Venus, and other places. “

China has big ambitions for its lunar exploration program. One possible mission would be a robotic sample returning from the far side of the moon – an area called Antarctic Basin – Aitken. One of the oldest and largest impact craters, parts of the lunar mantle may be exposed at the bottom of the basin. Rock samples can also be dated radiographically, giving an accurate date of impact.

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