Scientists presented the first detailed results of examination of samples from the far side of the Moon collected by the Chinese Chang'e 6 probe. Analysis of their composition indicated that volcanic activity took place there between three and four billion years ago. This is crucial information for understanding the distinct differences between the hemispheres of the Silver Globe.
So far, scientists have learned about the history of the Moon only using rocks brought from the area facing our planet. The Chang'e 6 mission in June brought samples from the far side of our natural satellite to Earth for the first time in human history, providing a unique opportunity to study volcanic activity there. The probe collected almost two kilograms of lunar soil.
– Solving the mystery of the volcanic history of the far side of the Moon is crucial to understanding the dichotomy of its hemispheres, emphasized Professor Li Qiu-Li from the Chinese Academy of Sciences.
The asymmetry between the two sides of the Moon, including differences in basalt distribution, topography, crust thickness and thorium concentration, has long been a mystery.
Four billion years ago
The Chinese team carried out isotopic dating of 108 basalt fragments delivered from the Moon. 107 of them revealed a consistent formation age of approximately 2,807 million years ago, which also indicates the age of eruption of local basalts at the probe landing site. This volcanic episode from 2.8 billion years ago has not been observed in samples from the visible side of the Moon, scientists emphasize.
However, the age of another fragment of basalt, with high aluminum content, was determined to be approximately 4,203 million years old. According to the analysis, it comes from a region south of the Chang'e 6 landing site. It is the oldest sample of lunar basalt whose age has been precisely estimated.
These data indicate that volcanic activity on the far side of the Moon lasted at least 1.4 billion years – from 4.2 to 2.8 billion years ago.
Visualization of the far side of the Moon based on data from the LRO probeNASA Scientific Visualization Studio
Preliminary lead isotope analysis further suggests that the basalts come from different sources. Basalt from 4.2 billion years ago came from a source rich in potassium, rare earth elements and phosphorus, while basalt from 2.8 billion years ago came from a source poor in these substances.
Hope for further research
The close correspondence between the 2.8 billion-year-old age of the basalt and estimates based on crater counts suggests that the crater-based chronological model developed from observations of the visible side of the Moon also applies to the other hemisphere.
As researchers emphasize in the journal Nature, the isotopic age of basalts from the Chang'e 6 mission is also an important calibration point for improving methods of learning about the history of the Moon based on counting craters on the surface of the Silver Globe.
In 2020, China brought samples of lunar soil to Earth from the side of the Moon visible from Earth. Previously, this was last achieved as part of the American Apollo program in the 1970s.
Main photo source: NASA Scientific Visualization Studio