The moon isn’t made of cheese after all. Detailed research has shown that the inner core of the Moon is, in fact, a solid ball with a density similar to that of iron. This, the researchers hope, will help resolve the long debate about whether the Moon’s interior 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,” wrote a team led by astronomer Arthur Bria from France’s National Center for Scientific Research in France, “challenge the evolution of the Moon’s magnetic field by demonstrating the existence of an inner core and support a global mantle overturning scenario that provides essential insights into the timeline of lunar bombardment.” in the first billion years of the solar system,” reports Science Alert.
Examining the internal composition of objects in the Solar System is most effectively achieved through seismic data. The way acoustic waves generated by earthquakes move and reflect off materials inside a planet or moon can help scientists create a detailed map of an object’s interior. We happen to have lunar seismic data collected by the Apollo mission, but their resolution is too low to accurately determine the state of the inner core. We know there is a fluid outer core, but what it contains remains under debate. The solid inner core and all-fluid core models work equally well with the Apollo data.
To figure it out once and for all, Brijom and his colleagues collected data from space missions and lunar laser experiments to compile a profile of various lunar features. These include the degree of its deformation due to its gravitational interaction with Earth, variations in its distance from Earth, and its density.
They then ran modeling with different core types to find which best matched the observational data and came up with several interesting findings. First, the models that most closely resemble what we know about the Moon describe active overturning deep within the lunar mantle. This means that the denser material inside the Moon falls towards the center and the less dense material rises upwards. This activity has long been proposed as a way to explain the presence of certain elements in volcanic regions of the Moon. The team’s research adds another point to the “for” evidence count.
And they discovered that the lunar core is very similar to Earth’s – with a liquid outer layer and a solid inner core. According to their modeling, the outer core has a radius of about 362 kilometers and the inner core has a radius of about 258 kilometers. That’s about 15 percent of the entire radius of the Moon. The inner core, the team found, also has a density of about 7,822 kilograms per cubic meter. It is very close to the density of iron. Interestingly, in 2011, a team led by NASA Marshall planetary scientist Rene Weber found a similar result using what were then state-of-the-art seismological techniques on Apollo data to study the lunar core. They found evidence of a solid inner core with a radius of about 240 kilometers and a density of about 8,000 kilograms per cubic meter. Their results, Briaud and his team say, confirm those earlier findings and make a pretty strong case for an Earth-like lunar core. And this has some interesting implications for the evolution of the Moon.
We know that shortly after the formation of the Moon, it had a strong magnetic field, which began to decline about 3.2 billion years ago. Such a magnetic field is generated by motion and convection in the core, so what the Moon’s core is made of is deeply relevant to how and why the magnetic field disappeared.
Given humanity’s hope to return to the moon in the relatively short term, we may not have to wait long for seismic verification of these findings.
Tags: Scientists finally confirmed moon
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