It’s official: Scientists finally confirm what’s going on inside the moon

Well, the verdict is in.

A thorough investigation published in May 2023 found that the moon’s core is actually a solid ball with a density similar to iron. Researchers hope this will help resolve the long-running debate over whether the moon’s core is solid or molten and lead to a more accurate understanding of the moon’s history and, by extension, the history of the solar system.

“Our results cast doubt on the evolution of the Moon’s magnetic field, as it demonstrates the existence of an inner core and supports a global mantle overturn,” wrote a team led by astronomer Arthur Bourriot of France’s National Center for Scientific Research. .” This scene provides insights into the timeline of lunar bombardment during the solar system’s first billion years.

The internal composition of objects in the solar system is most effectively probed through seismic data. The way sound waves from earthquakes travel through and reflect from the material inside a planet or moon can help scientists create detailed maps of the object’s interior.

We happen to have lunar seismic data collected by the Apollo missions, but the resolution is too low to accurately determine the state of the core. We know that a fluid outer core exists, but what it contains remains controversial. Models for solid cores and completely fluid cores are equally applicable to the Apollo data.

To figure this out once and for all, Breaud and his colleagues collected data from space missions and lunar laser ranging experiments to compile profiles of various lunar features. These include the degree of deformation caused by its interaction with Earth’s gravity, changes in distance from Earth, and its density.

Next, they modeled various core types to find the type that best matched the observations.

They made some interesting findings. First, the model most similar to what we know about the Moon describes active flipping deep in the lunar mantle. This means that denser material inside the moon falls toward the center, while less dense material rises upward. This activity has long been considered a way to explain the presence of certain elements in the moon’s volcanic regions. The team’s study adds another point to the “for” statistic of evidence.

They found that the moon’s core is very similar to Earth’s, with an outer fluid layer and a solid core. According to their model, the outer core has a radius of about 362 kilometers (225 miles) and the inner core has a radius of about 258 kilometers (160 miles). This is approximately 15% of the Moon’s entire radius.

The team found that the inner core also has a density of about 7,822 kilograms per cubic meter. This is very close to the density of iron.

Strangely, in 2011, a team led by NASA Marshall planetary scientist Renee Weber used the most advanced seismological technology at the time to conduct a lunar core study on Apollo data and found similar results. They found evidence of a solid core with a radius of about 240 kilometers and a density of about 8,000 kilograms per cubic meter.

Briaud and his team say their results confirm these earlier findings and provide fairly strong evidence for an Earth-like lunar core. This has some interesting implications for the evolution of the moon.

We know that the moon had a strong magnetic field soon after it formed, and it began to weaken about 3.2 billion years ago. Such magnetic fields are generated by motion and convection in the Earth’s core, so the composition of the moon’s core is closely related to how and why the magnetic field disappears.

Given humanity’s hopes of returning to the moon in a relatively short period of time, perhaps we won’t have to wait long for seismic verification of these findings.

The study was published in nature.

A version of this article was first published in May 2023.