South Pole Aitken Basin impact dated to early Moon history by Chang'e 6 samples

South Pole Aitken Basin impact dated to early Moon history by Chang'e 6 samples
by Simon Mansfield
Sydney, Australia (SPX) Mar 25, 2025

Scientists have precisely determined the age of the Moon's largest and most ancient impact crater, the South Pole-Aitken (SPA) basin, using rock samples retrieved by China's Chang'e-6 lunar mission. A research team led by Prof. CHEN YI at the Institute of Geology and Geophysics of the Chinese Academy of Sciences analyzed the first samples ever collected from the SPA region and established that the basin was formed approximately 4.25 billion years ago. This finding marks a significant advance in understanding both lunar and early Solar System history.

The SPA basin, spanning a vast expanse on the Moon's far side, is believed to have resulted from an intense bombardment of asteroids that occurred within the Solar System's first few hundred million years. Despite its prominence, determining the precise timing of the SPA impact has remained elusive due to the lack of direct sample analysis until now.

Previous age estimates of the SPA basin were largely speculative, relying on indirect measurements. The arrival of actual material from the SPA site, thanks to Chang'e-6, allowed scientists for the first time to date the impact event directly. Prof. CHEN's team focused on impact melt rocks contained within the returned lunar soil to determine when the SPA basin was formed.

"The South Pole-Aitken impact event produced a massive impact melt sheet," explained Prof. CHEN. "To precisely determine its formation age, we first need to identify the products of this impact melt sheet within the Chang'e-6 lunar soils."

In their study, researchers examined around 1,600 fragments from two soil samples. They identified 20 norite clasts that displayed unique textures, mineral compositions, and chemical signatures characteristic of impact formation. Using lead-lead isotopic dating of zirconium-bearing minerals found in these clasts, the team uncovered evidence of two ancient impact events - one 4.25 billion years ago and another 3.87 billion years ago. The older norite samples showed crystallization patterns indicating they formed within different layers of the impact melt sheet created by the SPA collision.

"Our extensive geological surveys and comparative lithological analyses of the SPA basin strongly suggest that the older impact age of 4.25 billion years most likely represents the timing of the SPA impact," Prof. CHEN stated.

This breakthrough offers the first sample-based confirmation that the SPA basin was formed about 320 million years after the Solar System's formation. The precise dating of the 4.25-billion-year-old impact provides a valuable reference point for improving the timeline of lunar impacts and offers deeper insight into the Moon's geological evolution.

Research Report:South Pole-Aitken massive impact 4.25 billion years ago revealed by Chang'e-6 samples