A lunar mystery solved? Researchers believe they have finally determined the age of the Moon’s oldest impact basin. A discovery that could well change our vision of the history of the Solar System, but also future lunar missions.
The South Pole-Aitken basin, gigantic and little-known, could be more than 4.32 billion years old. This colossal crater, located on the far side of the Moon, has intrigued scientists for decades.
b) Map of probability indices >0.5.
c) Close-up of the pixel boundaries of the Cabannes crater superimposed on a basic map.
d) Close-up of the pixel boundaries of Cabannes Crater superimposed on the unified USGS lunar geological map.
Geologists focused on a meteorite discovered in Algeria in 2005, called Northwest Africa 2995. The process used, called uranium-lead dating, is based on the natural disintegration of uranium into lead. Indeed, uranium, a radioactive element, transforms into lead at a predictable rate. By measuring this disintegration in the meteorite, the researchers obtained a surprising age: more than 4.32 billion years. A significant revision to previous estimates. Until now, scientists thought the largest lunar impacts took place between 4.2 and 3.8 billion years ago, an intense period nicknamed the Great Late Bombardment. But this new dating advances the age of the basin by 120 million years.
The interest of this discovery goes beyond simple lunar study. According to the team, Earth likely experienced similar impacts around this time. However, terrestrial geological activity has erased these traces, unlike the Moon, which preserves these events.
This advance was confirmed by comparing the data collected with those of NASA’s Lunar Prospector mission. The chemical similarities between the meteorite and the rocks of the South Pole-Aitken basin validated the provenance of this sample.
These results open up perspectives for future lunar missions. Sample returns from the basin could deepen our understanding of these primordial events.
What is uranium-lead dating?
Uranium-lead dating is a method of geological chronology used to determine the age of rocks and minerals. It is based on the radioactive disintegration of uranium into lead. Uranium naturally converts to lead at a constant rate over time.
The decay process occurs along two main chains: uranium-238 to lead-206 and uranium-235 to lead-207. Scientists measure the amounts of uranium and lead in a sample, then use their ratios to accurately calculate its age. This technique makes it possible to date materials several billion years old.
Why is the Moon a privileged witness to the history of the Earth?
The Moon retains traces of impacts and cosmic events that have been erased on Earth. Unlike our planetits geological activity is almost non-existent, which allows the craters and basins formed several billion years ago to still remain intact.
By studying lunar rocks, scientists can better understand the ancient periods of our Solar System. Impacts that hit the Moon and Earth in their early days left clues on the Moon, providing insight into the events that shaped our planet as well.
What is the Great Late Bombardment?
The Great Late Bombardment refers to a period in the history of the Solar System, approximately 4 billion years ago, during which the Earth, the Moon and other objects in the Solar System experienced an intense shower of asteroids and comets. This phase left numerous craters still visible today.
This period was identified thanks to the study of lunar samples brought back by the Apollo missions. Scientists believe these massive impacts shaped the planets’ surfaces, influencing the evolution of their atmospheres and geology.
