After decades of debate and speculation, scientists have finally confirmed the composition of the Moon’s core. A recent study published in May 2023 in Nature has revealed that the Moon’s inner core is a solid ball, with a density strikingly similar to that of iron.
This discovery resolves long-standing questions about the Moon’s internal structure and provides valuable new insights into the formation of the Moon, its history, and the early days of the Solar System.
The Scientific Breakthrough: A Closer Look at the Moon's Core
The study, led by Arthur Briaud of the French National Centre for Scientific Research, combined data from various space missions and lunar laser-ranging experiments to model the Moon’s internal structure. Using this data, the team confirmed that the Moon’s inner core is solid, with a radius of 258 kilometers (160 miles) and a density of 7,822 kilograms per cubic meter, which closely matches that of iron. Surrounding this inner core is a fluid outer core with a radius of approximately 362 kilometers (225 miles). Together, these layers account for about 15% of the Moon’s total radius.
This discovery builds on prior research. In 2011, a team led by Renee Weber, a planetary scientist at NASA’s Marshall Space Flight Center, suggested that the Moon had a solid inner core, based on seismic data from the Apollo missions. Weber’s team estimated the radius of the core to be around 240 kilometers, with a density of 8,000 kilograms per cubic meter.
The findings of Briaud’s team not only confirm Weber’s earlier results but also offer more refined measurements and a more detailed understanding of the Moon’s internal structure. “Our results,” Briaud’s team wrote, “support a global mantle overturn scenario that brings substantial insights on the timeline of the lunar bombardment in the first billion years of the Solar System.”
Implications for the Moon’s Magnetic History
One of the key revelations from this discovery is its impact on our understanding of the Moon's magnetic history. The Moon once had a strong magnetic field, much like Earth’s, which began to decline around 3.2 billion years ago.
Magnetic fields are generated by movement and convection within a planet's core, typically involving liquid iron. The confirmation of the solid core helps scientists piece together how the Moon’s magnetic field was generated and why it eventually disappeared.
The study suggests that the solid core played a role in the Moon’s magnetic field during its early history, contributing to the geodynamo effect before the field eventually weakened as the core cooled. “Such a magnetic field is generated by motion and convection in the core, so what the lunar core is made of is deeply relevant to how and why the magnetic field disappeared,” the researchers noted.
What This Means for Future Lunar Exploration
With humanity planning to return to the Moon through initiatives like NASA’s Artemis program, this new understanding of the Moon’s internal structure could play a crucial role in future missions. The confirmation of a solid core adds a new layer of complexity to our understanding of the Moon, and it provides valuable context for future seismic studies that may be conducted on the lunar surface.
These findings also provide a foundation for deeper exploration into the Moon’s geological evolution. Scientists now have a clearer picture of the Moon's internal composition, which can help guide future explorations aimed at uncovering more about its formation and its role in the early Solar System. Given the renewed interest in lunar exploration, Briaud’s team concluded, “Perhaps we won’t have long to wait for seismic verification of these findings.”