Chang'e-6 Samples Indicate Moon's Oldest Impact Crater Dates Back 4.25 Billion Years
Chang'e-6 samples have dated the Moon's oldest impact crater to 4 billion years ago.
TroibNews 
Based on research involving lunar samples collected by the Chang'e-6 mission, a team of Chinese scientists has confirmed that the South Pole-Aitken (SPA) basin, the moon's oldest and largest impact crater, was formed 4.25 billion years ago. This discovery is crucial for understanding the early evolution of both the moon and the solar system.
In a study published Friday in National Science Review, the research team, led by Chen Yi from the Institute of Geology and Geophysics under the Chinese Academy of Sciences, analyzed samples returned by the Chang'e-6 mission, precisely dating the formation of the SPA basin to 4.25 billion years ago.
The SPA basin is a massive impact scar located on the far side of the moon, likely created during a period when asteroids bombarded much of the solar system shortly after its formation. Despite its significance, accurately dating the basin has proven challenging.
Previous indirect estimates of the timing of the SPA impact have varied widely, ranging from 4.26 to 4.35 billion years ago. Planetary scientists have long sought direct evidence—specifically rock samples from the SPA basin—to better understand the moon and the solar system.
China's Chang'e-6 mission successfully returned the first samples from the SPA basin, providing a long-awaited opportunity for direct dating of the basin. However, the Chang'e-6 lander touched down in the mare basalt region of the Apollo Basin within the SPA Basin, an area that has undergone multiple impacts and experienced basaltic eruptions following the SPA impact. This complexity means that the lunar samples collected by Chang'e-6 contain fragments from various geological periods, complicating efforts to accurately date the SPA basin.
"The SPA impact event produced a massive impact melt sheet," Chen explained. "To precisely determine its formation age, we first need to identify the products of this impact melt sheet in the Chang'e-6 lunar samples."
The research team scrutinized approximately 1,600 fragments from 5 grams of lunar samples, identifying 20 representative norite clasts with textures, mineralogy, and geochemistry that indicated they originated from an impact. By employing precise lead-lead dating of zirconium-bearing minerals within these clasts, the scientists uncovered evidence of two distinct impact events occurring at 4.25 billion years and 3.87 billion years ago. The older norites, which date back to 4.25 billion years, displayed structural and compositional characteristics suggesting they crystallized at different levels within the same impact melt sheet produced by the SPA impact.
Extensive geological surveys and comparative lithological analyses of the SPA basin strongly indicate that the earlier impact age of 4.25 billion years is likely to represent the timing of the SPA impact, Chen added.
This finding marks the first direct, sample-based evidence confirming that the moon's largest impact basin formed approximately 320 million years after the solar system's inception. The definitive age of 4.25 billion years for the SPA basin serves as a critical reference point for refining the lunar cratering timeline and establishing a more comprehensive historical sequence of the moon's early evolution.
The Chang'e-6 probe was launched from China on May 3, 2024, and on June 25, 2024, its returner landed in northern China, bringing back 1,935.3 grams of lunar samples from the far side of the moon.
Anna Muller contributed to this article for TROIB News
In a study published Friday in National Science Review, the research team, led by Chen Yi from the Institute of Geology and Geophysics under the Chinese Academy of Sciences, analyzed samples returned by the Chang'e-6 mission, precisely dating the formation of the SPA basin to 4.25 billion years ago.
The SPA basin is a massive impact scar located on the far side of the moon, likely created during a period when asteroids bombarded much of the solar system shortly after its formation. Despite its significance, accurately dating the basin has proven challenging.
Previous indirect estimates of the timing of the SPA impact have varied widely, ranging from 4.26 to 4.35 billion years ago. Planetary scientists have long sought direct evidence—specifically rock samples from the SPA basin—to better understand the moon and the solar system.
China's Chang'e-6 mission successfully returned the first samples from the SPA basin, providing a long-awaited opportunity for direct dating of the basin. However, the Chang'e-6 lander touched down in the mare basalt region of the Apollo Basin within the SPA Basin, an area that has undergone multiple impacts and experienced basaltic eruptions following the SPA impact. This complexity means that the lunar samples collected by Chang'e-6 contain fragments from various geological periods, complicating efforts to accurately date the SPA basin.
"The SPA impact event produced a massive impact melt sheet," Chen explained. "To precisely determine its formation age, we first need to identify the products of this impact melt sheet in the Chang'e-6 lunar samples."
The research team scrutinized approximately 1,600 fragments from 5 grams of lunar samples, identifying 20 representative norite clasts with textures, mineralogy, and geochemistry that indicated they originated from an impact. By employing precise lead-lead dating of zirconium-bearing minerals within these clasts, the scientists uncovered evidence of two distinct impact events occurring at 4.25 billion years and 3.87 billion years ago. The older norites, which date back to 4.25 billion years, displayed structural and compositional characteristics suggesting they crystallized at different levels within the same impact melt sheet produced by the SPA impact.
Extensive geological surveys and comparative lithological analyses of the SPA basin strongly indicate that the earlier impact age of 4.25 billion years is likely to represent the timing of the SPA impact, Chen added.
This finding marks the first direct, sample-based evidence confirming that the moon's largest impact basin formed approximately 320 million years after the solar system's inception. The definitive age of 4.25 billion years for the SPA basin serves as a critical reference point for refining the lunar cratering timeline and establishing a more comprehensive historical sequence of the moon's early evolution.
The Chang'e-6 probe was launched from China on May 3, 2024, and on June 25, 2024, its returner landed in northern China, bringing back 1,935.3 grams of lunar samples from the far side of the moon.
Anna Muller contributed to this article for TROIB News
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