How do we date the surface of the Moon? Lunar chronology models are created by combining two methods: crater counting and radiometric age dating. Crater counting is a widely used technique in which the observed crater size-frequency distribution for a given surface is fitted to a known crater production rate. The rationale behind this method is that the longer a surface has been exposed to impacts, the more craters will pockmark its surface. This technique has also been used to provide ages for many other bodies within the solar system. The crater-counting age can then be anchored and calibrated to radiometric age dates obtained for samples returned from the Moon, to build an absolute age model.

The recent Chang’e 5 mission, which landed on the far side of the Moon on December 1, 2020, returned more than 1 kilogram of lunar basaltic material just over two weeks later. Some of this material provided a radiometric isotope age of 2.03 billion years, which falls within the large gap of ages previously obtained on lunar samples (between 1 to 3 billion years), representing almost half of the history of the Moon. New work by Zongyu Yue and coworkers of the Chinese Academy of Sciences used this new age to update the most widely used crater chronology model for the Moon. The new age data acts as a crucial anchor point and allowed the authors to create a more reliable model applicable to future research. This model gives older ages than the previous chronology for nearly all surfaces, with a maximum difference of approximately 240 million years at the 2.55-billion-year mark. The new model should enhance the reliability of ages estimated with crater counting not only on the Moon but across the inner solar system. READ MORE