Did the Moon endure a cataclysmic bombardment in its early history? New evidence from China's Chang'e-6 mission challenges a long-held theory, but here's where it gets controversial...
In a groundbreaking study published in Science Advances, scientists from the Chinese Academy of Sciences (CAS) and collaborating institutions have upended our understanding of the Moon's impact history. By analyzing samples retrieved from the far side of the Moon by the Chang'e-6 mission—a feat never before accomplished—researchers have revised the decades-old lunar crater chronology model. And this is the part most people miss: the findings suggest that the Moon’s early impact history was far more gradual than previously thought, contradicting the widely debated Late Heavy Bombardment (LHB) hypothesis.
Impact craters, the Moon’s most striking features, have long served as a record of meteorite collisions since its formation. Early telescopic observations by Galileo laid the groundwork, but it was the Apollo and Luna missions that allowed scientists to quantitatively link crater density to surface age. This relationship, known as the lunar cratering chronology function (CF), became the cornerstone of lunar geology, enabling age estimates for regions without samples. However, a critical limitation persisted: all calibration samples came exclusively from the Moon’s near side, leaving doubts about the model’s global applicability.
But here's where it gets controversial: the Chang'e-6 mission, which landed in the ancient South Pole-Aitken (SPA) Basin on the far side, provided the missing piece. The returned samples, including 2.807-billion-year-old basalt and 4.247-billion-year-old norites, offered the first far-side calibration points. Surprisingly, the data revealed no measurable difference in impact flux between the near and far sides, debunking earlier theories of intensified far-side bombardment. This supports a unified global cratering chronology—a bold claim that challenges previous assumptions.
The study also tackles the LHB hypothesis, which suggests a sudden spike in impacts around 3.9 billion years ago. While Apollo samples seemed to support this, the Chang'e-6 data tells a different story. The 4.247-billion-year-old norites, representing crystallized impact melts from the SPA Basin’s formation, indicate a smooth and rapid decline in impacts during the Moon’s early history, rather than a dramatic spike. Is the LHB hypothesis truly dead, or are we missing something?
These findings not only resolve long-standing debates but also provide a more accurate framework for dating unsampled lunar regions. Yet, they raise provocative questions: If the Moon didn’t experience a late heavy bombardment, what does this mean for the inner Solar System’s history? Could our understanding of planetary formation be due for a rewrite? The Chang'e-6 mission has opened a new chapter in lunar science, but the story is far from over. What do you think? Does this study mark the end of the LHB hypothesis, or is there more to uncover?
Topographic map of the lunar farside based on LRO LOLA Data. (Image by YUE Zongyu's team)
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