Earth’s tidally locked Moon always presents the same face to us, yet its mysterious far side features significant differences, which scientists are beginning to understand more clearly thanks to new samples returned by China’s Chang’e-6 mission.
In 2023, China launched its Chang’e-6 mission to the Moon’s less explored far side, successfully collecting nearly 2,000 grams of material from the South Pole–Aitken Basin—the oldest, deepest, and largest known lunar impact structure. The region’s stark contrasts in topography, crustal thickness, and volcanic history, compared to the near side, have made it a compelling target for scientific study.
The South Pole-Aitken Basin
Orbital observations have long hinted at the disparities between the Moon’s near and far sides, but remote sensing alone can’t tell the full story. Theories ranging from lunar magma ocean crystallization to major impact events have been proposed to explain the differences, yet all have lacked direct evidence. While many missions dating back to Apollo 11 in 1969 have returned lunar samples, none had previously come from the Moon’s far side.
The South Pole–Aitken Basin, a vast and ancient crater, has long intrigued scientists. Earlier studies estimated it formed around 4.25 billion years ago and resulted from an impact event with energy exceeding that of a trillion atomic bombs. Yet how such a massive collision influenced the Moon’s geological evolution remained largely speculative—until now.
Describing the Far Side of the Moon
The new samples from Chang’e-6 serve as the basis for four papers recently published in Nature. Each study focuses on a different aspect of lunar history, offering fresh insights into the Moon’s evolution, including its volcanic activity, magnetic field, water content, and mantle composition.
Surprisingly, one study suggests that the Moon experienced significant volcanic activity for a minimum of 1.4 billion years, from approximately 4.2 to 2.8 billion years ago, far eclipsing earlier estimates. Also at the 2.8 billion-year-old mark, the lunar magnetic field experienced a significant rebound, which Chinese scientists believe indicates highly irregular fluctuations in the lunar dynamo. Those determinations were made based on paleomagnetic measurements collected from basalt clasts.
One intriguing element of the findings illustrates the depth of the Moon’s asymmetry. Far less water content resides on the far side of the Moon than on the near side, which suggests that volatile elements are unevenly distributed inside the Moon. Finally, extreme impact events likely had a significant role in shaping the Moon’s interior. This is indicated by the geochemical analysis of basalt, which suggests an ultra-depleted mantle source. Researchers believe this resulted from melt extraction due to the impacts of a primordial, depleted mantle.
A Lunar Collaboration
The findings represent a collaborative effort among several Chinese scientific institutions, including the Chinese Academy of Sciences’ Institute of Geology and Geophysics and National Astronomical Observatories, as well as Nanjing University. Professor Wu Fuyuan of the Institute of Geology and Geophysics noted that these studies are the first to provide a detailed picture of the long-term geological effects of the 4.5 billion-year-old impact event.
Each institution contributed to building a comprehensive understanding of the samples. The National Astronomical Observatories, along with its collaborators, led the initial analysis of the physical, mineralogical, and geochemical characteristics of the South Pole–Aitken Basin material. The Guangzhou Institute of Geochemistry confirmed the 2.8-billion-year age of the volcanic activity and established its likely link to heavy mantle depletion.
Meanwhile, the Institute of Geology and Geophysics dated the impact that created the basin to approximately 4.25 billion years ago, providing a key reference point for assessing other early solar system collisions.
The paper “Ultra-depleted Mantle Source of Basalts from the South Pole–Aitken Basin” appeared on July 9, 2025, in Nature.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.