A lunar mystery solved? Researchers believe they have finally determined the age of the Moon's oldest impact basin. A discovery that could reshape our understanding of the history of the Solar System, as well as future lunar missions.
The gigantic and little-known South Pole-Aitken basin may be over 4.32 billion years old. This colossal crater, located on the far side of the Moon, has intrigued scientists for decades.
a) Map of probability indices >0.
b) Map of probability indices >0.5.
c) Close-up of the Cabannes crater pixel boundaries superimposed on a basic map.
d) Close-up of the Cabannes crater pixel boundaries superimposed on the USGS unified lunar geological map.
Geologists focused on a meteorite discovered in Algeria in 2005, named Northwest Africa 2995. The process used, called uranium-lead dating, relies on the natural decay of uranium into lead. Uranium, being a radioactive element, transforms into lead at a predictable rate.
By measuring this decay in the meteorite, researchers obtained a surprising age: over 4.32 billion years. This is an important revision to previous estimates. Until now, scientists believed that the largest lunar impacts occurred between 4.2 and 3.8 billion years ago, a period of intense activity known as the Late Heavy Bombardment. However, this new dating brings the age of the basin forward by 120 million years.
The significance of this discovery transcends lunar study. According to the team, Earth likely experienced similar impacts during this time. However, Earth's geological activity has erased these traces, unlike the Moon, which serves as a preserver of these events.
This advancement was confirmed by comparing the data collected with that of NASA's Lunar Prospector mission. The chemical similarities between the meteorite and rocks from the South Pole-Aitken basin verified the source of this sample.
These results open up new possibilities 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 geological chronology method used to determine the age of rocks and minerals. It is based on the radioactive decay of uranium into lead. Uranium naturally transforms into lead at a constant rate over time.
The decay process follows two main chains: uranium-238 into lead-206 and uranium-235 into lead-207. Scientists measure the quantities of uranium and lead in a sample, then use their ratios to calculate its age with precision. This technique allows for dating materials that are billions of years old.
Why is the Moon a privileged witness to Earth's history?
The Moon preserves traces of impacts and cosmic events that have been erased on Earth. Unlike our planet, its geological activity is almost non-existent, allowing craters and basins formed billions of years ago to remain intact.
By studying lunar rocks, scientists can better understand the ancient periods of our Solar System. The impacts that affected both the Moon and the Earth in their early days left clues on the Moon, providing a glimpse into the events that also shaped our planet.
What is the Late Heavy Bombardment?
The Late Heavy Bombardment refers to a period in the history of the Solar System, around 4 billion years ago, during which the Earth, Moon, and other objects in the Solar System were subjected to an intense asteroid and comet shower. This phase left many craters still visible today.
This period was identified through the study of lunar samples brought back by the Apollo missions. Scientists believe that these massive impacts shaped the surfaces of planets, influencing the evolution of their atmospheres and geology.
Article author: Cédric DEPOND