China's Chang'e-6 Mission Redefines Lunar History, Challenging "Late Heavy Bombardment" Theory

Global - Ekhbary News Agency

China's Chang'e-6 Mission Redefines Lunar History, Challenging "Late Heavy Bombardment" Theory

The scientific community is abuzz with the initial findings from the lunar samples meticulously collected by China’s Chang’e-6 mission. This monumental undertaking successfully retrieved material from the Moon's far side, a feat that marks a significant leap in our understanding of Earth's closest celestial neighbor. These precious samples offer an unprecedented close-up view of the far side's geological composition and historical timeline, providing crucial data that challenges some long-standing theories about the early solar system. A recent paper published in *Science Advances* by researchers from the Chinese Academy of Sciences has unveiled particularly compelling insights, prompting a potential paradigm shift in lunar chronology and the broader narrative of planetary formation.

For decades, our direct geological understanding of the Moon has been almost exclusively derived from samples obtained from its near side, the hemisphere perpetually facing Earth. These samples, brought back by Apollo missions and other probes, have been exhaustively analyzed, forming the bedrock of our current knowledge regarding the Moon's formative years. However, the far side has remained largely a mystery, its secrets guarded by the immense logistical challenges of accessing it. The Moon itself acts as a formidable communication barrier, necessitating sophisticated relay satellites to maintain contact with any mission operating on its hidden face. China’s National Space Administration (CNSA) boldly embraced this challenge, achieving the historic first successful far-side landing with its Chang’e-4 mission. The subsequent Chang’e-6 mission in 2024 built upon this success, becoming the pioneering endeavor to return samples directly from this enigmatic lunar terrain.

Scientists have been working tirelessly to analyze the returned lunar regolith and rock fragments, and their initial publications are already yielding profound implications. The *Science Advances* paper, formally released in February, highlights three pivotal discoveries. Firstly, and perhaps less surprisingly, the study indicates a remarkable similarity in the ages of craters observed on both the near and far sides of the Moon. This finding aligns with the logical expectation that both hemispheres would be exposed to a consistent rate of cosmic impacts over geological timescales, a hypothesis that lacked direct empirical proof until now.

Secondly, the research suggests a necessary recalibration of the lunar chronology function, a mathematical model used by scientists to estimate the age of lunar surfaces by counting visible impact craters. Historically, this function has been calibrated using data exclusively from near-side samples. The inclusion of far-side data points reveals a notable shift, proposing an adjustment of approximately 340 million years for certain lunar features. While significant, this adjustment represents less than a 10% variation within the Moon's vast 4-billion-year history, refining rather than overturning existing models.

However, the third and arguably most revolutionary finding directly confronts one of the most widely accepted theories in planetary science: the "Late Heavy Bombardment" (LHB). The LHB theory posits a period of intense asteroid and comet impacts across the inner solar system, including Earth and the Moon, roughly 3.9 billion years ago. This catastrophic event was thought to be triggered by gravitational perturbations from the migrating outer planets, scattering a deluge of debris into the inner solar system. Evidence for the LHB has largely stemmed from the prevalence of 3.9-billion-year-old impact melt rocks found in near-side lunar samples, leading scientists to believe that many of the Moon's prominent craters date back to this tumultuous era.

The Chang’e-6 samples, however, introduce a compelling counter-narrative. Among the collected materials, researchers identified norite, a mineral believed to be a direct relic of the massive impact that formed the South-Pole Aitken (SPA) Basin – the largest and one of the oldest impact structures on the Moon. Using sophisticated lead-lead dating techniques, which measure the decay of uranium isotopes into lead isotopes, scientists determined the age of the SPA Basin to be approximately 4.25 billion years old. This age predates the theorized onset of the LHB by a substantial margin, calling into question the notion of a global, synchronous bombardment event at 3.9 billion years ago.

The paper proposes an alternative explanation for the cluster of 3.9-billion-year-old craters observed on the near side. Instead of a solar-system-wide bombardment, these craters might be largely attributed to a single, exceptionally violent event: the Imbrium impact. This colossal impact could have ejected vast amounts of debris across the near side, creating numerous secondary craters that would subsequently be dated to around 3.9 billion years, thereby skewing the overall chronological record from near-side samples. Furthermore, a broader analysis of crater age distribution now suggests a more gradual, steady decline in impact frequency since the Moon's formation, rather than a chaotic spike. This pattern aligns more closely with a scenario where the newly formed planets and moons gradually cleared out their orbital neighborhoods.

These findings from the Chang’e-6 mission are not merely refining lunar history; they are reshaping our fundamental understanding of how the solar system evolved. By providing direct evidence from the Moon's far side, scientists can now construct a more complete and accurate timeline of cosmic events. The implications extend beyond our Moon, potentially influencing models of planetary accretion and bombardment across the entire inner solar system. As more papers emerge from the ongoing analysis of these unique lunar samples, the scientific community eagerly anticipates further revelations that will undoubtedly continue to enrich our knowledge of the universe's profound past.

Ekhbary News Agency