Chinese scientists have analyzed samples of basalt collected on the far side of the Moon. They indicate that the mantle beneath this region is much drier than on the visible side. This could be the result of a giant collision.
Analysis of lunar basalts
Chinese scientists have discovered that the lunar mantle on the far side of the Moon contains less water than on the near side, based on analysis of basalts collected by the Chang’e-6 lunar mission. This interesting conclusion was reached by a team led by Prof. Hu Sen from the Institute of Geology and Geophysics, Chinese Academy of Sciences.
The results of the study, published in the journal Nature, show that the mantle source of Chang’e-6 shale basalts contains 1-1.5 µg/g of water, indicating that the mantle on the far side of the Moon is drier than on the near side. This result may provide important insights into the formation and thermochemical evolution of the Moon.
Uneven distribution of elements
Over the past two decades, extensive studies of lunar samples from the near side of the moon have demonstrated a very heterogeneous distribution of water in the Moon’s interior, with concentrations ranging from about 1 to 200 µg/g.
In particular, the crust in the area of the huge KREEP rock outlet in the Oceanus Procellarum on the near side of the Moon, has higher thorium concentrations than the other two major geochemical provinces of the Moon: the Feldspathic Highlands and the South Pole–Aitken Basin on the far side of the Moon.
Both thorium and water are considered incompatible elements during magmatic processes, meaning that they preferentially remain in the melt rather than being part of crystallizing minerals. This geochemical behavior suggests that the mantle beneath the SPA basin, on the far side of the Moon, may contain less water.
To confirm this hypothesis, the research team focused on analyzing the water and hydrogen isotope content of melt inclusions and apatite in the Chang’e-6 shale basalts, the first samples returned from the far side of the SPA basin.
Disproportion of water distribution in the mantle
The team’s results indicate that the parent magma of these basalts contains 15-168 µg/g water. In addition, the team has estimated that the mantle source of the Chang’e-6 basalts has a water content of 1-1.5 μg/g, which is much lower than that of the adjacent mantle.
This disparity indicates a potential hemispherical dichotomy in the internal distribution of water on the Moon, reflecting many of the asymmetric features observed on the lunar surface.
This new estimate of the water content of the Moon’s distant mantle signals a significant step forward in improving our understanding of the water content of our moon’s voluminous silicate mantle. It places important constraints on the giant impact hypothesis of the Moon’s origin and emphasizes the role of water in its long-term evolution.
According to phys.org
