China’s Chang’e-6 mission made history by retrieving the first surface samples from the moon’s far side, revealing evidence of volcanic activity spanning 1.4 billion years. Reuters reports: Researchers said on Friday the soil brought back from the Chang’e-6 landing site contained fragments of volcanic rock – basalt – dating to 4.2 billion years ago and to 2.8 billion years ago. This points to a long period of volcanic activity – at least 1.4 billion years – on the far side during the first half of the moon’s history, when it was a more dynamic world than it is today. The moon, like Earth, formed about 4.5 billion years ago. Volcanism on the moon, Earth and other planetary bodies involves the eruption of molten rock from the mantle – the layer just under the outer crust – onto the surface. The landing site in the South Pole-Aitken Basin, an impact crater, is an area with the thinnest crust on the moon, helpful for finding evidence of volcanism.
The samples contained various volcanic rock fragments, and the researchers used a method called radioisotope dating to determine their age. Lunar basalt samples previously were obtained from the moon’s near side, which perpetually faces Earth, during U.S. Apollo, Soviet Luna and Chinese Chang’e-5 missions. These showed that volcanism on the near side had occurred as long ago as 4.0 billion years ago and continued for at least two billion years, Li said. “The exact timing and duration of lunar volcanism is elusive and maybe varied across different regions. Some small-scale volcanism may have also occurred on the near side as late as about 120 million years ago as recorded by volcanic glass beads from Chang’e-5 samples” collected in 2020, Li said.
The new study also found that the basalt dating to 4.2 billion years ago differed in composition from the basalt dating to 2.8 billion years ago, meaning they originated from different sources of molten rock – magma – in the mantle, Li said. The Chang’e-6 samples, Li said, also differ in composition compared with previously collected lunar samples from the near side.
