Moon's magnetic past explained

A recent study has confirmed a significant breakthrough in our understanding of the Moon’s interior.

Well, the verdict is in: the Moon is definitely not made of green cheese, Caliber.Az reports, citing foreign media.

A comprehensive study published in May 2023 has revealed that the Moon’s inner core is actually a solid sphere with a density comparable to iron. This finding is expected to resolve a long-standing debate about whether the Moon’s core is solid or molten and enhance our understanding of the Moon’s history—and by extension, the history of the Solar System.

According to the team led by astronomer Arthur Briaud from the French National Centre for Scientific Research, their findings "challenge previous notions about the evolution of the Moon's magnetic field by confirming the presence of a solid inner core. This supports a global mantle overturn scenario, offering significant insights into the timeline of lunar bombardment during the early years of the Solar System."

Understanding the internal composition of celestial bodies is best achieved through seismic data. By analyzing how acoustic waves from quakes travel through and reflect off materials inside a planet or moon, scientists can create detailed maps of these objects' interiors.

We have lunar seismic data from the Apollo missions, but its resolution is insufficient to accurately determine the state of the Moon’s inner core. While it’s established that the Moon has a fluid outer core, the nature of the inner core remains uncertain. Both models proposing a solid inner core and those suggesting an entirely fluid core fit the Apollo data equally well.

To resolve this, Briaud and his team gathered data from space missions and lunar laser-ranging experiments to create a profile of various lunar characteristics. They examined the Moon's deformation from gravitational interactions with Earth, its distance variations, and its density.

Their modeling efforts revealed several key findings. The models that best matched the observational data indicated significant activity within the lunar mantle, with denser material sinking toward the center and less dense material rising. This process, previously suggested to explain the presence of certain elements in volcanic regions, now has additional supporting evidence from their research.

The team also found that the Moon’s core closely resembles Earth’s core, featuring a fluid outer layer and a solid inner core. Their models suggest that the outer core has a radius of about 362 kilometers (225 miles), while the inner core has a radius of approximately 258 kilometers (160 miles)—about 15% of the Moon's total radius. The inner core’s density was estimated at 7,822 kilograms per cubic meter, comparable to iron.

Interestingly, a 2011 study led by NASA Marshall planetary scientist Renee Weber, using advanced seismological techniques on Apollo data, also suggested the presence of a solid inner core. Weber’s team found a solid inner core with a radius of about 240 kilometers and a density of around 8,000 kilograms per cubic meter.

Briaud and his team believe their findings confirm earlier results and provide strong evidence for a Moon core similar to Earth’s. This has intriguing implications for understanding the Moon's evolution.

We know that shortly after its formation, the Moon possessed a strong magnetic field, which began to wane around 3.2 billion years ago. Such a magnetic field is generated by movement and convection within the core, so understanding the composition of the lunar core is crucial to explaining the decline of this field.

With plans for humanity to return to the Moon in the near future, we may soon have the opportunity to verify these results through further seismic studies.