Modelling has shown that a long meteorite bombardment could turn up to a third of the graphite on the planet's surface into sparkling diamond crystals.
Unshrouded by a dense atmosphere and devoid of plate tectonics, Mercury remains virtually defenceless against impacts from celestial bodies and retains the scars they have created for a long time. For billions of years, meteorites have bombarded its surface, now densely cratered. The energy of these impacts is sufficient to convert a large proportion of the carbon present there as graphite into diamond crystals.
On Earth, such a transformation takes place in the interior, at a depth of at least 150 kilometres, where temperatures and pressures reach enormous values. However, for a short time they can rise to the right values even during meteorite strikes. Just such a mechanism may work on Mercury. American geologist Kevin Cannon spoke about it at the 53rd International Lunar and Planetary Science Conference (LPSC 2022).
The surface of the nearest planet to the Sun resembles that of the Moon, it is also riddled with craters, plateaus and vast plains like lunar seas. In ancient times it was lavishly flooded by lava, so its crust is rich in sulphur compounds and volcanic minerals. Some areas, however, are much darker and contain large amounts of carbon in the form of ordinary black graphite, which may have precipitated and crystallized from the lava as it cooled.
These areas were subsequently meteoritically bombarded and Kevin Cannon ran computer simulations of such processes. The model assumed that Mercury's 25-kilometre crust contained a 300-metre thick layer of graphite. It also showed that meteorite impacts over 4.5 billion years may have converted up to a third of that amount into diamonds. Cannon calculated that the planet could contain an order of magnitude more such crystals than Earth - 16 quadrillion tonnes.
The model did not take into account the processes involved in the breakdown of diamonds under the same meteorite impacts. However, according to Cannon, they could not destroy a noticeable part of the diamonds: their melting point exceeds 4000 ° C and they can survive most such tests. The scientist adds that it will be possible to check the calculations soon enough: in 2025, the BepiColombo probe will arrive in Mercury's orbit and will be able to study the planet up close. If there are indeed enough diamonds on the surface, it will distinguish this signal in the infrared spectrum.
