For decades, researchers have been studying the Moon. NASA and China are even racing to send humans to the lunar surface. However, before that mission, scientists had already discovered what was inside the Earth's only natural satellite.
What's Inside the Moon?
In May 2023, researchers published the study "The lunar solid inner core and the mantle overturn," revealing what was inside the Moon. They learned that it has a fluid outer core and a solid inner core similar to Earth's. The inner core of the Moon is around 500 kilometers in diameter, or 15% of its entire diameter, and is composed of a metal with a density comparable to that of iron.
"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," the researchers wrote.
The study used the lunar seismic data collected by the Apollo mission. However, the resolution was too low to determine the inner core's state accurately. Although they were sure that the Moon has a fluid outer core, what encompasses the surface remained a debate.
Both fully fluid and solid inner core models perform comparably with Apollo data. Arthur Briaud of the French National Centre for Scientific Research in France, an astronomer and lead author of the study, and his colleagues assembled information from satellite flights and lunar laser range studies to create a profile of different lunar features to solve the puzzle finally. These include the density of it, the change in its distance from Earth, and the degree of deformation caused by its gravitational interaction with Earth.
They then experimented with different core kinds of modeling to see which matched the empirical data the best. They came to some intriguing conclusions.
First, active overturn is described as occurring deep into the lunar mantle in the models that most nearly match their knowledge of the Moon. This implies that less dense stuff climbs upward, and denser material descends into the Moon's center. This process has long been proposed to explain why specific elements are found in the Moon's volcanic areas.
They also discovered that the lunar core is extremely similar to the Earth's core, with a solid inner core and an outer fluid layer. Their simulation indicates that the radius of the inner core is around 258 kilometers (160 miles), and that of the outer core is approximately 362 kilometers (225 miles). That represents around 15% of the Moon's total radius.
The scientists also discovered that the inner core's density is around 7,822 kg/cubic meter, which is highly similar to iron's density.
Moon Flipped 4.2 Billion Years Ago
Some aspects of the Moon have scientists scratching their heads. But it all made sense when they discovered that the Moon had turned inside out billions of years ago.
The Moon's returned basaltic lava rock contained very high titanium concentrations. Moreover, satellite data indicates that most lunar volcanic rocks rich in titanium are found on the moon's nearside.
They learned that the Moon flipped itself billions of years ago, and this explained how some pebbles got to where they were and why they were not widely distributed.
"The moon is fundamentally lopsided in every respect," research co-author and LPL associate professor Jeff Andrews-Hanna said. "For the first time, we have physical evidence showing us what was happening in the Moon's interior during this critical stage of its evolution, and that's exciting.
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