Moon’s far side rocks challenge long-held asteroid bombardment theory

Ancient samples from the Moon's far side are reshaping scientists' understanding of how asteroid impacts shaped the early Solar System, with new research suggesting bombardment declined gradually over billions of years rather than occurring as a single catastrophic burst.

Chang'e-6 Samples Challenge Long-Held Theory

A study published July 23 in Science Advances presents 28 single-clast argon-argon ages of impact melt rocks returned by China's Chang'e-6 mission, revealing impact events spanning from about 4.33 to 1.13 billion years ago. The findings allow scientists to reconstruct more than three billion years of lunar impact history and challenge the Late Heavy Bombardment hypothesis — the idea that the inner Solar System experienced a sudden, intense spike in asteroid impacts around 3.9 billion years ago.eurekalert+1

"The lunar farside bombardment was not dominated by a cataclysmic spike," said Wanfeng Zhang, an engineer at the Guangzhou Institute of Geochemistry in China, according to Science News.sciencenews

The study was led by the State Key Laboratory of Deep Earth Processes and Resources at the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, with contributions from researchers at Curtin University in Western Australia.eurekalert

A Cleaner Record From the Far Side

The Chang'e-6 mission, which returned samples from the lunar far side in June 2024, provided material from the Apollo crater within the South Pole-Aitken Basin — the Moon's largest and oldest impact structure. The far side samples are considered particularly valuable because the region was less affected by later geological events than the near side.eurekalert

Dr. Fred Jourdan, from Curtin University's School of Earth and Planetary Sciences, said the samples showed no evidence of a concentrated bombardment event. "These samples are helping us rewrite parts of the Moon's history and suggest the early Solar System experienced a long decline in asteroid impacts rather than a single catastrophic bombardment," he said.eurekalert

The ages of the Chang'e-6 samples showed no clustering around 3.9 billion years ago, instead pointing to a steady decline in impact frequency over time. Earlier analysis of Chang'e-6 data published in February also found that impact fluxes on the Moon's near and far sides are essentially consistent, supporting a unified global cratering chronology.phys+2

Implications for Earth's Early History

Because the Moon and Earth formed together, the lunar impact record offers indirect evidence about conditions on early Earth, where erosion and plate tectonics have erased most traces of ancient bombardment. Dr. Jourdan noted that "every major impact recorded on the Moon tells us something about the conditions experienced by the young Earth," including events that may have influenced the emergence of life.eurekalert