What’s in the Moon’s inner core? Scientists have found the answer!

Is it solid or molten? For decades, scientists have debated about what’s in the Moon’s core. Well, looks like they have finally got an answer to it.
A new study published in has found that the Moon has a solid inner core with a density similar to that of iron.
A research team led by astronomer Arthur Briaud from the French National Centre for Scientific Research explored what’s inside the Moon. They used data from space missions and lunar laser-ranging experiments to develop models that best fit the Moon’s known characteristics. Their findings have finally given crucial insights into the Moon’s history and, by extension, the evolution of the Solar System.

"Our results question the evolution of the Moon's magnetic field thanks to its demonstration of the existence of the inner core and 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,” astronomer Arthur Briaud of the French National Centre for Scientific Research in France wrote in the study.
Seismic data is the most effective way to understand the interiors of celestial bodies. Though Apollo mission seismic data uncovered the presence of a fluid outer core, it failed to determine whether the inner core was solid or molten. Inorder to understand it, Briaud’s team analyzed data on the Moon’s gravitational deformation, distance variations from Earth, and density. These models further confirmed that the Moon's structure closely resembles Earth’s core, with an outer fluid layer and a solid inner core.

As per their calculations, the Moon’s outer core has a radius of about 362 kilometers (225 miles). The solid inner core has a radius of approximately 258 kilometers (160 miles), which makes up about 15% of the Moon’s total radius. The inner core’s density is estimated at 7,822 kilograms per cubic meter, which is very close to that of iron.

Interestingly, the new findings strike similarity with a 2011 study led by NASA Marshall planetary scientist Renee Weber, which also suggested a solid inner core with a similar density. However, Briaud’s new research has underlined the case for an Earth-like lunar core.

Moon’s magnetic field was once strong but began to decline around 3.2 billion years ago. As magnetic fields are generated by core convection, understanding the Moon’s core composition may explain why its field disappeared. Given humanity’s ambitious plans to return to the Moon in the near future through missions like NASA’s Artemis program and other international lunar exploration efforts, the recent findings have further added hope.