Scientists Reveal Secrets of the Moon’s Inner Core

A team of scientists from the French National Centre for Scientific Research has resolved the long-standing debate about the moon’s inner core, concluding that it is solid rather than molten. Their findings, published in Nature in May of last year, reveal that the moon’s inner core is a solid ball with a density similar to iron.

The team, led by astronomer Arthur Briaud, explained that their research sheds light on the evolution of the moon’s magnetic field. They also support a theory called global mantle overturn, which provides valuable insights into the timeline of the moon’s bombardment during the early years of the Solar System.

Seismic data is often used to study the interior of celestial bodies, and in this case, the team utilized this data to create a detailed map of the moon’s inner structure. They analyzed how acoustic waves, produced by quakes, travel through the moon and reflect off its materials. While the Apollo missions provided some seismic data, its resolution was insufficient for drawing precise conclusions. While it was known that the moon’s outer core is fluid, the composition of the layer beneath it remained uncertain, with both solid and liquid core models fitting the Apollo data.

To resolve this, Briaud and his team combined data from several space missions and laser-ranging experiments to compare the moon’s characteristics with different core models. Their analysis suggested that denser materials are found at the moon’s center, with lighter materials rising towards the surface, which also helps explain the elements found in volcanic regions.

The research determined that the moon’s core has a fluid outer layer and a solid inner core, much like Earth’s. According to their model, the outer core’s radius is approximately 362 kilometers (225 miles), while the inner core measures around 258 kilometers (160 miles), making up about 15 percent of the moon’s total radius.

Additionally, the team estimated the moon’s overall density at 7,822 kilograms per cubic meter, which is comparable to the density of iron. This finding corroborates similar results from a 2011 study led by NASA planetary scientist Renee Weber, confirming that the moon’s core is much like Earth’s.

Understanding the composition of the moon’s core is crucial for studying the decline of its magnetic field, which began around 3.2 billion years ago. The magnetic field was initially strong, and its gradual weakening is believed to be the result of motion and convection inside the core.