New Moon revelations: Solid inner core reshapes lunar history

Scientists now better understand the structure of the Moon's interior. Evidence suggests that it is a solid sphere with a density akin to iron. Researchers claim that their findings "challenge the evolution of the Moon's magnetic field by demonstrating the existence of an inner core and support the scenario of a global mantle overturn, providing significant insights into the Moon's bombardment timeline during the first billion years of the Solar System."

Studies of the internal composition of objects in the Solar System are most effective when using seismic data. Scientists use information on how acoustic waves, generated by earthquakes, move and reflect off matter inside a planet or satellite. Thanks to such data, scientists should even be able to create a detailed map of the interior of a given body.

As reported on ScienceAlert, we have lunar seismic data from the Apollo missions, but their resolution is quite low. We know that the Moon's outer core is liquid. However, there were still ongoing discussions about what surrounds it.

To resolve the uncertainties, Arthur Briaud from the French National Centre for Scientific Research gathered data from space missions and laser ranging experiments of the Moon to create a profile of various lunar features. These include the degree of deformation of our satellite due to its gravitational interaction with Earth, the variability of its distance from Earth, and its density. The next step was to conduct modelling with different types of cores to find a solution that matches the observations.

The researchers' findings indicate that models describing active overturn deep in the lunar mantle most closely resemble the factual state. This suggests that denser material inside the Moon falls towards the centre, while less dense material rises.

The researchers' findings indicate that the Moon's core is similar to Earth's—with an outer liquid layer and a solid inner core. They assert that the radius of the outer core is about 360 kilometres, and the inner core is about 260 kilometres, which is about 15 percent of the Moon's radius. The density of the inner core is reported to be approximately 7,850 kilograms per cubic metre.

In 2011, research led by NASA palaeontologist Renee Weber reached similar conclusions – they found that the inner core has a radius of 240 kilometres and a density of about 8,010 kilograms per cubic metre. According to Briaud and his team, this discovery significantly impacts our understanding of the Moon's evolution.