A moon rock collected over fifty years ago by Apollo 17 astronauts could well overturn our understanding of the Moon's earliest moments and the Solar System. This seemingly ordinary fragment contains information that challenges established scientific timelines.
The sample numbered 76535 has a particular chemical composition and texture indicating it formed nearly fifty kilometers (about 31 miles) beneath the lunar surface. Radioisotope dating reveals it has been exposed on the surface for 4.25 billion years. These characteristics show a deep origin, unlike most moon rocks studied until now.
Eugene Cernan driving a lunar rover during the Apollo 17 mission before its final assembly (cameras and antennas are not installed).
NASA Image.
Computer simulations conducted by Evan Bjonnes of Lawrence Livermore National Laboratory show how this sample could have reached the surface without suffering the typical damage from a violent impact. During the formation of an impact crater, the floor collapses and allows deep materials to rise gently through the liquefied crust. This mechanism would explain the absence of shock traces or scars on the rock, unlike what is usually observed.
This discovery implies that the Mare Serenitatis basin, where the sample was collected, is much older than previously estimated. If its formation dates back 4.25 billion years, this pushes its age back by three hundred million years. This temporal revision could apply to other lunar impact basins, thus changing our perception of the Moon's geological history.
The consequences extend beyond our natural satellite. The Moon serves as a reference for dating impacts in the early Solar System, because its surface preserves traces that erosion has erased on Earth, Venus, or Mars. A recalibration of lunar events therefore directly influences the chronology of other planets, offering new insight into the conditions that prevailed during Earth's youth.
Future crewed missions to the Moon will allow verification of these hypotheses by collecting other similar samples. If comparable processes occurred in other lunar seas, astronauts could bring back rocks that will confirm or refute this scenario.
Radioisotope dating
Radioisotope dating is a scientific method that determines the age of rocks by measuring the decay of radioactive elements they contain. Certain isotopes, like potassium-40 or uranium-238, gradually transform into other elements at a constant rate called half-life. By analyzing the ratios between the parent isotope and the daughter isotope, geologists can calculate the time elapsed since the rock formed.
This technique relies on the principle that minerals crystallize by trapping radioactive atoms. Once the system is closed, radioactive decay begins and follows a predictable curve. For the Moon, where geological activity is almost nonexistent, radioactive clocks often remain intact for billions of years, offering extremely precise dating.
Technological advances have refined these measurements, reducing error margins to just a few million years. This makes it possible to distinguish between closely spaced events in lunar history, such as the formation of different impact basins.
In planetary science, radioisotope dating is important for establishing comparative chronologies between celestial bodies. It helps reconstruct the history of the Solar System by providing reliable temporal benchmarks, essential for understanding the evolution of planets and their primitive environments.