Now, the mystery has been solved.
A groundbreaking study has confirmed that the Moon has a solid inner core, much like Earth’s, and this discovery could rewrite our understanding of the Moon’s formation and its role in shaping the Solar System.
A Long-Standing Lunar Mystery—Solved
A comprehensive analysis published in May 2023 has settled the debate: the Moon’s inner core is a solid iron-rich sphere, much denser than previously thought.
This revelation not only reshapes our perception of the Moon but also has implications for understanding planetary evolution throughout the cosmos.
The study, led by Arthur Briaud and his team at the French National Centre for Scientific Research, presents compelling evidence confirming the presence of a solid inner core surrounded by a fluid outer layer.
The findings align with previous hypotheses, but this time, they come with an added layer of certainty.
How Scientists Probed the Moon’s Core Without Drilling
Unlike Earth, where geologists can directly study the planet’s interior using seismic activity, exploring the Moon’s depths is far more challenging.
Since no direct samples from the Moon’s core exist, scientists had to get creative.
They used a combination of data from lunar seismic activity, spacecraft observations, and lunar laser-ranging experiments to construct a detailed model of the Moon’s interior.
The Apollo missions provided some seismic data, but the low resolution left questions unanswered.
To bridge this gap, Briaud and his team combined Apollo data with measurements of the Moon’s deformation due to Earth’s gravity, its orbital variations, and its density.
The results? A near-exact match between observational data and models that feature an Earth-like fluid outer core and a solid inner core.
The Earth-Like Core of the Moon
The study estimates that the Moon’s outer core has a radius of 362 kilometers (225 miles), while the inner core is 258 kilometers (160 miles) wide—about 15% of the Moon’s total radius.
This solid core is incredibly dense, measuring about 7,822 kg/m³, close to that of pure iron.
Challenging the Assumption That the Moon Was Geologically Dead
For years, many scientists believed that the Moon was a geologically dead body, with no significant internal activity.
However, these new findings challenge that assumption.
The presence of a dense, solid core suggests that the Moon once had a powerful magnetic field—one that existed billions of years ago but has since faded.
Planetary magnetic fields are typically generated by the movement of liquid iron within the core, meaning the Moon’s inner structure once played a crucial role in generating its now-extinct magnetic field.
What This Means for Lunar History and Future Exploration
These findings don’t just settle a long-standing debate—they provide critical insights into the Moon’s past.
Scientists now believe that the Moon’s core played a vital role in its early magnetic field, which was active 3.2 billion years ago before mysteriously shutting down.
Understanding this evolution helps us piece together how planetary bodies develop and change over time.
This is crucial not just for our Moon but for understanding how other moons and rocky planets—including exoplanets in distant star systems—might evolve.
A Confirmation Over a Decade in the Making
Interestingly, a similar study in 2011, led by NASA planetary scientist Renee Weber, had already suggested that the Moon’s core was structured like Earth’s.
At the time, Weber’s team estimated a solid inner core of 240 kilometers and a density close to 8,000 kg/m³.
Briaud’s 2023 research confirms and strengthens those findings, bringing us one step closer to fully understanding our celestial neighbor.
Will We Get Direct Evidence?
While these findings provide a highly detailed and reliable picture of the Moon’s core, scientists still need direct seismic confirmation—something that may happen within our lifetime.
With NASA’s Artemis program aiming to return humans to the Moon, new instruments could be placed on the lunar surface to conduct higher-resolution seismic studies.
This would allow scientists to observe how moonquakes travel through the Moon’s interior, confirming once and for all the structure of its core.
Why This Matters Beyond the Moon
The study of the Moon’s core extends far beyond lunar science.
Understanding how and why the Moon’s magnetic field disappeared could provide insights into why Mars lost its atmosphere, why Venus evolved so differently from Earth, and how planets across the universe form and change over time.
The Moon, once thought to be a lifeless rock in space, continues to surprise us.
And with future missions planned, the next decade of lunar exploration could unlock even more secrets hidden beneath its surface.
