Chang'e-6 samples pinpoint moon's oldest crater to 4.25 billion years ago

Chang'e-6 samples pinpoint moon's oldest crater to 4.25 billion years ago
by Clarence Oxford
Los Angeles CA (SPX) Mar 21, 2025

Chinese scientists have precisely dated the moon's oldest and largest impact feature, the South Pole-Aitken (SPA) basin, to 4.25 billion years ago using lunar samples returned by the Chang'e-6 mission. This result offers critical insights into the moon's formative history and the early development of the solar system.

A research team led by Chen Yi from the Institute of Geology and Geophysics under the Chinese Academy of Sciences conducted the study, which was published Friday in *National Science Review*. Their analysis of the Chang'e-6 samples marks the first time scientists have directly dated the SPA basin.

Located on the moon's far side, the SPA basin is a vast impact scar likely created during a period of intense asteroid bombardment in the solar system's early days. Prior estimates of its age varied between 4.26 and 4.35 billion years, based solely on indirect methods. Until now, planetary scientists lacked direct evidence from SPA materials to definitively date the event.

The Chang'e-6 mission changed that by delivering the first samples from the SPA region. However, the spacecraft landed specifically within the Apollo Basin, a mare basalt area inside SPA that has experienced subsequent impacts and volcanic activity. As a result, the collected samples included fragments from different geological periods, complicating efforts to pinpoint SPA's formation date.

"The SPA impact event produced a massive impact melt sheet," explained Chen. "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."

From 5 grams of returned samples, researchers sorted through about 1,600 fragments and identified 20 norite clasts exhibiting the texture, mineral content, and geochemistry indicative of impact origin. By performing lead-lead dating on zirconium-bearing minerals within these norites, the team identified two significant impact events, one at 4.25 billion years ago and another at 3.87 billion years ago.

The older norites, dating back 4.25 billion years, demonstrated features suggesting they crystallized at varying depths within the same impact melt sheet generated by the SPA impact. According to Chen, extensive geological surveys and rock analyses strongly support the conclusion that this 4.25-billion-year mark reflects the SPA basin's formation.

This discovery constitutes the first direct, sample-based proof that the moon's largest impact basin formed about 320 million years after the solar system began. The confirmed age offers a critical reference point for refining lunar cratering timelines and mapping out the moon's early geological history.

Launched on May 3, 2024, the Chang'e-6 probe returned to Earth on June 25, 2024, landing in northern China with 1,935.3 grams of lunar material collected from the moon's far side.