2024-07-19 06:41:43
The surface of the planet is unusually rich in carbon – more precisely, graphite. So many carbonaceous asteroids could not have fallen to Mercury, so most of the carbon must be primordial – it appeared together with the planet. Hence, Mercury’s magma ocean once contained a lot of dissolved carbon, which later crystallized as graphite.
Now scientists have calculated that graphite was not necessarily the only crystalline form of carbon, and that there may be a layer of diamonds up to tens of kilometers thick in the depths of Mercury.
The crystal formation of carbon – or any other element – depends on the solidification temperature. The authors of the new study examined the circumstances and progress of mercury solidification, based on both new theoretical models and recent experimental data on the behavior of carbon under high pressure and temperature conditions.
If Mercury’s magma ocean was composed entirely of iron and silicates (well, with carbon impurities), graphite was surely the only likely crystalline form of carbon. But there was probably a lot of sulfur there too, which changed the properties of the magma so that diamonds could also crystallize from it.
It is possible that the diamonds crystallized before the magma solidified, but this scenario is unlikely. It is much more likely that the diamond crystallized as the magma solidified, with the crystals sinking to the mantle-core boundary, about 400 kilometers below the planet’s surface. Meanwhile, the diamonds forming in the core rose up, also up to this limit. It is likely that a layer of diamonds as thick as 15-18 kilometers has accumulated there.
Of course, we have no way to reach it, but the high thermal conductivity of the diamond helps to equalize the core and mantle temperatures – which affects the movement of the core material and the generation of the magnetic field.
Similar conditions could have occurred on various carbon-rich exoplanets, so the effect of diamond layers should be taken into account when modeling their climates and magnetic fields.
The results of the study are published žurnale „Nature Communications“.
2024-07-19 06:41:43