Astronomers puzzled over its structure for years before spacecraft landed on the moon. In the early part of the 20th century, there was debate over whether the moon was stony like Martian moons or had a more complicated geology. The discussion is over.

Like Earth, the Moon has a fluid outer core and a solid inner core, according to models. The Moon’s inner core is 500 kilometers wide and consists of a metal akin to iron. Nature published the study.

In their paper, the researchers wrote, “Our results question the evolution of the Moon 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.”

Unexpected Moon structure

Seismic data is ideal for Solar System object composition analysis. Because seismic waves—essentially acoustic waves—propagate differently via different materials. Quake waves flow through planets and moons differently depending on what they pass through. Apollo seismic data is too low-resolution to establish the core’s status.

French researchers built a lunar feature profile from space mission and lunar laser range data to find a solution. Its density and distance from Earth are examples. To match observed data, they modeled core kinds.

The team made many discoveries. First, they discovered that denser Moon material sinks toward the center and less dense stuff rises. Researchers have proposed this to explain specific components in Moon volcanic zones. That’s only one aspect.

Researchers say the lunar core, like Earth’s, has a fluid outer layer and a solid inner core. 15% of the Moon’s width is its 500-kilometer core. In 2011, NASA specialists used seismological methods using Apollo data to analyze the lunar core and obtained a similar conclusion.

The discovery illuminates the Moon’s structure, but its magnetic field’s fate remains a mystery. About 3.2 billion years ago, the Moon’s magnetic field started to weaken. Core motion and convection created the field.

New lunar missions by government organizations and commercial space businesses may provide more data for research. NASA, ispace, Astrobotic, and Intuitive Machines aim to deploy four people on the Artemis II mission in 2024 to fly near the moon.