What material is the moon’s core composed of? < The- Are you curious? < Daily Post-Series < Article text

ㅣDaily Post = Reporter Kim Jeong-eunㅣThe moon is a very familiar celestial body, but many things remain unclear about its composition and environment.

According to a paper published by the French National Center for Scientific Research (CNRS) in the international journal Nature in May 2023, there is a ‘solid core made of metal’ on the moon.

In fact, research into the moon’s internal structure has been ongoing for a long time. Seismic data is known to be effective in determining the internal composition of celestial bodies. This is because seismic waves pass through the interior of a celestial body, and by analyzing the way the vibration propagates, the constituent materials and structure of the interior of the celestial body can be estimated.

In a paper published in 2011, an analysis result was derived based on Apollo program seismometer data that ‘the inner core of a solid is covered by the outer core of a fluid.’ At the time, NASA planetary scientist Lenny Weber analyzed the moon’s seismic data and concluded, “The moon has a solid inner core.”

However, the 2011 study could not determine what material the inner core was made of due to problems with the accuracy of the seismometer.

Accordingly, the research team at the French National Center for Scientific Research took a different approach from existing analyses. First, detailed observation data of the moon (mass, density, rotation method, deformation of the moon due to tides, change in distance between the Earth and the Moon, etc.) were collected through laser distance measurement data. In addition, through simulations assuming various core materials, the material that best matches the observation data was discovered.

As a result of the analysis, it was revealed that the moon has an ‘inner core composed of metal with a density close to iron (7822 kg/㎥)’.

According to this model, the radius of the moon’s outer core is about 362 km. Additionally, the size of the inner core is 258 km in radius, which is equivalent to about 15% of the entire volume of the moon.

It was also revealed that during the formation of the moon, a mantle overturn occurred, in which the composition of the core and mantle changed. The occurrence of mantle overturning helps explain why large amounts of iron exist near the lunar surface.