Researchers from the Côte d’Azur University and the Institute for Celestial Mechanics and Ephemeris Calculations in France developed models of the Moon’s interior and found evidence suggesting that the inner core is solid, like Earth’s. They determined that not only is the Moon’s inner core solid like Earth’s, but it is also made of a metal with a density close to that of iron. They also found that the core is about 310 miles (500 kilometers) in diameter, about 15% of the Moon’s total width. Arthur Briaud and his collaborators published their work this week in the journal Nature.

The new analysis also yielded evidence of lunar mantle rollover, or movement of material in the Moon’s mantle before it cools into a mostly solid mass. Scientists argue that this shifting of the mantle could explain why there is iron on the lunar surface. As warmer material rose through the mantle, volcanic activity on the Moon deposited iron on the surface, where it eventually cooled and decayed in the ground.

This further reaffirms what NASA had published, which suggested in 2011 that the Moon had a solid iron-rich core, as well as a fluid outer core. Those researchers used seismic data taken during the Apollo missions to paint a picture of what the inner layers of the Moon look like. That work estimated the inner core to have a diameter of about 300 miles (482 kilometers), which is close to the group’s recent estimates.

source: https://www.nature.com/articles/s41586-023-05935-7