惑星科学：嫦娥6号のサンプルが裏側の月火山活動の年代を特定

The landing site of the Chang’e-6 mission on the farside of the Moon was volcanically active approximately 2.8 billion years ago, according to one of the first published analyses of material returned by the mission. The study, published in Nature, suggests that there was volcanic activity on the basaltic mare (flat plains) in this region for more than 1.4 billion years.

Lunar samples returned to Earth by the Apollo, Luna and Chang’e-5 missions have established that volcanism took place on the nearside of the Moon between 4–2 billion years ago. However, the lack of samples from the farside of the lunar surface means it has not been possible to confirm the timing of volcanic activity for this region. Earlier this year, the Chang’e-6 mission retrieved samples from the Apollo basin located in the north-eastern South Pole–Aitken basin, an area with the thinnest crust on the Moon, providing an opportunity to study farside volcanism.

Qiu-Li Li and colleagues analysed fragments of basalt (a type of volcanic rock) contained in two samples of soil collected by Chang’e-6. Using a process called lead–lead dating, which measures lead isotopes to determine the age of samples, the authors analysed 108 basalt fragments. They found that one fragment of high-alumina basalt was around 4.2 billion years old. However, the majority of the studied basalt fragments had a consistent formation age of around 2.8 billion years ago. The authors suggest this represents the age of the main volcanic episode at the Chang’e-6 landing site, which they note is a surprisingly young eruption and not recognized from observations taken from samples from the nearside of the Moon.