Unveiling the Lunar Secrets: Detection of a Solid Core

Rendering of the moon’s interior composition. A progression from the surface to the center displays a thin crust, a substantially thick mantle, a region of low viscosity at the boundary between core and mantle, a liquid outer core, and a solid inner core. Credit: © Géoazur/Nicolas Sarter

Scientists have recently made groundbreaking discoveries about the moon, revealing that it has a solid core and shedding light on the existence of iron-rich substances on its surface.

Using a combination of various research methods, these scientists have successfully mapped out the moon’s internal structure. They have ascertained the presence of a solid core within the moon, similar to the Earth’s core. Their findings also give credence to the theory of ‘mantle overturn’ and provide an explanation for the presence of iron-rich elements on the lunar surface.

Over fifty years since Apollo 11 facilitated the first lunar surveys, a scientific team has unveiled information about the moon’s internal structure that has until now remained elusive. They confirmed that the moon indeed has a solid core, similar to the Earth’s. Along with this discovery, they have also provided evidence that clarifies why iron-rich materials exist in the lunar crust. The research group comprised individuals from CNRS, Université Côte d’Azur, the Côte d’Azur Observatory, Sorbonne Université, and the Paris Observatory-PSL, with their findings recently featured in the journal Nature.

Resolving Disputes: The Moon’s Innermost Structure

While questions about the moon’s formation and evolution persist, the nature of its deep interior has been established. More than half a century after the inaugural space missions to the moon, it is indisputable that the moon possesses a solid inner core enveloped by a liquid outer core, mirroring the Earth’s structure. This hypothesis has now been validated by the efforts of scientists from several prestigious institutions.

Uncovering the Solid Inner Core

Around twenty years after the identification of a liquid outer core, the team has brought to light a solid inner core, roughly 500 km in diameter, which comprises about 15% of the moon’s total size. This core is composed of a metal similar in density to iron. Various methods tied to the moon’s rotation had previously enabled clear identification of the fluid outer core. However, the smaller size of the solid core made it difficult to detect until now. Its existence has been confirmed through data gathered from different space missions and from lunar laser ranging.

Clarifying Iron-Rich Elements: The Lunar Mantle Overturn

Apart from this significant discovery, the scientists have found evidence supporting the theory of material movement within the mantle, the layer between the core and the crust, during the moon’s evolution. This phenomenon, known as the lunar mantle overturn, helps explain the presence of iron-rich elements on the moon’s surface.

This process likely occurred when material rose to the surface, creating volcanic rocks that were incorporated into the lunar crust. Afterward, the materials that were denser compared to the surrounding crustal material descended back down to the core-mantle boundary.

Implications for the Solar System’s Understanding

These revelations considerably enhance our comprehension of the solar system’s history and certain occurrences such as the fading of the lunar magnetic field. Initially, the lunar magnetic field was a hundred times stronger than Earth’s current magnetic field, but it has now become virtually non-existent.

Reference: “The lunar solid inner core and the mantle overturn” by Arthur Briaud, Clément Ganino, Agnès Fienga, Anthony Mémin, and Nicolas Rambaux, 3 May 2023, Nature. DOI: 10.1038/s41586-023-05935-7

Notes

The research was conducted at the Géoazur laboratory (CNRS/Observatoire Côte d ‘Azur/IRD/Université Côte d’Azur) and the Institute for Celestial Mechanics and Computation of Epherimides (IMCCE) (Observatoire de Paris-PSL/CNRS). The project was funded by the French National Research Agency (ANR-19-CE31-0026), and an ERC AstroGeo Advanced Grant (885250).

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More about Lunar solid core

• The Lunar Solid Inner Core and the Mantle Overturn
• Moon’s Internal Structure
• Understanding Moon’s Magnetic Field
• Information about Lunar Laser Ranging
• Apollo 11 Mission
• CNRS
• Université Côte d’Azur
• Côte d’Azur Observatory
• Sorbonne Université
• Paris Observatory-PSL