The Moon opens its heart for the first time

  • Research
Published on May 5, 2023 Updated on July 4, 2023

on the May 5, 2023

moon core
moon core

Fifty years after Apollo 11 paved the way for the first studies of the Moon, a team of scientists from CNRS, Université Côte d'Azur, Côte d'Azur Observatory, Sorbonne University and the Paris Observatory-PSL has revealed a part of its internal structure that has up until now remained a mystery: the Moon has a solid core, like the Earth. Along with this discovery, additional data also explains the presence of iron-rich materials in the lunar crust. This work was published in Nature on May 3, 2023. 

While the evolution of the Moon is still debated, the nature of its inner structure has now been settled. Fifty years after the first space missions to the Moon, no doubt remains: it has a solid core in the center and a fluid outer core, like the Earth. This hypothesis has just been validated thanks to work carried out by scientists from CNRS, Université Côte d'Azur, Côte d'Azur Observatory, Sorbonne University and the Paris Observatory-PSL. 

About twenty years after the identification of a fluid outer core, the team1  has revealed a solid core about 500 km in diameter, or about 15% of the size of the Moon. It is composed of a metal whose density is close to that of iron. Techniques related to the rotation of the Moon had made it possible to clearly identify the fluid outer core. However, the solid core remained undetectable due to its small size. Its existence has now been proven2  thanks to the use of data from different space missions and lunar laser telemetry.  

In addition to this major discovery, the scientists have uncovered evidence to support the hypothesis of material movements in the mantle, the intermediate layer between the nucleus and the crust of the Moon, during its evolution. This is called the lunar mantle overturn and it helps explain the presence of iron-rich material on the surface of the Moon. How did this phenomenon occur? Material may have risen to the surface, depositing volcanic rocks in the lunar crust. Then, the elements too dense relative to the surrounding material in the crust fell back to the interface between the mantle and the core. 

This work provides crucial knowledge for understanding the history of the solar system and particular events, such as the disappearance of the lunar magnetic field: originally a hundred times stronger than the current magnetic field of the Earth, it is now almost non-existent.

CNRS researcher | Arthur Briaud | T +33 4 83 61 85 69 |
Côte d'Azur Observatory astronomer | Agnès Fienga | 
CNRS press | Bastien Florenty | T +33 1 44 96 51 26 |


1- Working at the Géoazur laboratory (CNRS/Côte d'Azur Observatory/IRD/Université Côte d'Azur) and at the Institute for Celestial Mechanics and Computation of Ephemerides (Paris Observatory-PSL/CNRS).
2- These results were obtained thanks to funding from the National Research Agency (ANR-19-CE31-0026), and an ERC Advanced AstroGeo Fellowship (885250). 


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