China’s Chang’e-6 mission has been exploring the largest crater on the Moon. It’s known as Aitken Basin and is found at the South Pole of the Moon where craters are permanently shadowed. The crater is a whopping 2,500 km across and measures 10km deep and Chang’e-6 data has revealed that a giant asteroid smashed into the Moon about 4.25 billion years ago.
There are of course plenty of craters on the Moon which is Earth’s only natural satellite. It’s a fascinating object that has captivated human imagination ever since we started looking at the sky. At an average distance of 384,400km from Earth it reflects sunlight appearing to go through a regular cycle of phases as it orbits. Even the casual observer can see it’s a barren, cratered world and this has been backed up by a number of lunar missions. The Apollo missions have of course been the most well known but there has been a flotilla of automated probe exploring our nearest neighbour.
The Moon
Chang’e-6 is one such mission that has been exploring the Moon. It’s purpose is to collect and return samples from the far side of the Moon and follows on from Chang’e-5. It was launched in May 2024, and was designed to target the South Pole-Aitken basin, thought to be one of the oldest impact craters in the Solar System. The primary objective was to land on the far side of the Moon, a region never before directly sampled and collect around 2kg of lunar material.
Scientists led by Chen Yi from the Chinese Academy of Sciences have used data from Chang’e-6 to precisely date the formation of Aitken Basin and report their findings in the National Science Review. It’s well understood that large craters tend to be among the oldest in the Solar System and Aitken Basin was thought to be one of them. The team found that, by analysing the samples returned by Chang’e-6 it dates back 4.25 billion years!
The Moon’s largest impact feature, the South Pole–Aitken basin, is so named because it stretches between Aitken crater and the south pole. (Credit : NASA/GSFC)
To reach their conclusion, the team examined approximately 1,600 fragments from 5 grams of lunar samples. They were able to identify 20 representative norite clasts (a type of coarse grained igneous rock often found in the Earth’s crust) that helped to reveal the Moon’s geological history. Using a technique known as lead-lead dating where the ratio of different lead isotopies are determined they found evidence of two impact events at 4.25 and 3.87 billion years ago. The older impact showed signs of crystallisation at different levels suggesting it was the original event.
Planetary scientists studying crater formation have been keen to get their hands on direct rock samples from the Aitken Basin to resolve a long standing conflict where its age estimates range from 4.26 to 4.35 billion years. However, Chang’e-6 landing site within the Apollo Basin area made things a little challenging as they contain fragments from a number of geological periods due to various impacts and eruptions. The complexity of the area made dating the basin especially difficult.
The Chang’e-6 mission has finally provided evidence about the Moon’s early history, precisely dating the formation of the Aitken Basin just 320 million years after the formation of the Solar System. Since its launch, it returned 1,935.3 grams of lunar samples to north China, completing their delivery on 25 June 2024. Chen Yi’s team have finally established the age of the Basin creating a much needed anchor point for the chronological list of events in the early lunar history.
Source : Chang’e-6 samples date moon’s oldest impact crater to 4.25 billion years ago