If we compare Mercury to Venus and Mars, we will see that the planet, in addition to being extremely hot, is little explored. However, this is about to change. A recent discovery could forever change the way we see the smallest planet in the Solar System. And why? Researchers have discovered signs of something unusual inside it. We are talking about a structure that is almost 18 kilometers thick, highly resistant to heat and that may be linked to the fact that the planet maintains an active magnetic field, which is an extremely rare phenomenon for such a small and inhospitable body.
It seems that Mercury has been hiding secrets
It all started with NASA’s MESSENGER mission, which mapped the composition of Mercury’s surface. Until one detail caught the attention of experts: the abundant presence of graphite, which is also a form of carbon, spread throughout the planet’s crust. It was then that this discovery pointed to an unusual origin: an ancient ocean of carbon-rich magma.
What we always thought was that over time, this ocean would have cooled, causing the lighter carbon to rise and darken the crust, while the heavier materials, including dense carbon, sank. But then what happened to this carbon buried deep within Mercury?
That was the question that guided an international team of scientists, led by Dr. Yanhao Lin of the High Pressure Advanced Research Center (HPSTAR). From there, they recreated in the laboratory the extreme conditions of Mercury’s interior, using a high-volume press to simulate pressures above 7 GPa and temperatures exceeding 3,600 °F. Until finally the mystery began to reveal itself.
The diamond layer that changed everything
What the researchers found was that under these conditions, the carbon that sank into Mercury’s mantle didn’t remain as graphite. It turned into a diamond (unlike any other diamond we’ve ever seen in mines like this). Yes, diamond. And not exactly in the shape of a sphere, but as a thick, solid layer surrounding the planet’s metallic core. This layer can be up to 18 km thick, forming a sort of crystalline shell between the core and the mantle.
However, the most surprising thing is not the aesthetics of the discovery itself, but rather its consequences. What does this mean? Well, diamond has an extremely high thermal conductivity, which means it helps dissipate heat from the core to the mantle more efficiently. This allows Mercury’s liquid core to continue generating enough internal movement to maintain an active magnetic field, something that had previously puzzled scientists since small planets tend to lose this mechanism over time. Not stopping there, the sulfur present in Mercury’s interior also reduces the melting point of magma, which facilitates the formation and accumulation of diamonds at the boundary between the core and mantle.
What other planets like Mercury are out there?
And why does this discovery have such an impact on us? Well, the implications go far beyond Mercury… That’s because, unlike Earth, Mars, or Venus, which lost much of their carbon through geological or atmospheric processes, Mercury appears to have preserved this element. First, it was preserved as graphite in the crust and now as diamond in the depths.
All of this makes Mercury a chemically distinct planet and raises the possibility that other rocky bodies, including carbon-rich asteroids, may have undergone similar processes. So the question remains: if small amounts of pressure and carbon are enough to form diamonds, could there be bright worlds hidden in the Solar System? Well, we don’t know if it’s bright, but Planet Nine, which has been well hidden out there, is about to be found.
