'Forbidden' substances may help sustain life on super-Earths

Moscow: Super-Earths could contain compounds 'forbidden' by the classical rules of chemistry that may increase the heat transfer rate and strengthen the magnetic field, making these planets favourable for living organisms, scientists say.

Researchers used an algorithm called USPEX to find out which compounds may be formed by silicon, oxygen and magnesium at high pressures.

"Earth-like planets consist of a thin silicate crust, a silicate-oxide mantle - which makes up approximately 7/8 of the Earth's volume and consists more than 90 per cent of silicates and magnesium oxide - and an iron core," said Artem Oganov, head of the Moscow Institute of Physics and Technology (MIPT) Laboratory of Computer Design.

"We can say that magnesium, oxygen, and silicon form the basis of chemistry on Earth and on Earth-like planets," said Oganov.

Researchers studied various structural compositions of Mg-Si-O that may occur at pressures ranging from 5 to 30 million atmospheres.

Such pressures may exist in the interior of super-Earths - planets with a solid surface mass several times greater than the mass of the Earth.

The results of the computer modelling show that the interior of these planets may contain the "exotic" compounds MgSi3O12 and MgSiO6. They have many more oxygen atoms than the
MgSiO3 on Earth.

"Their properties are very different to normal compounds of magnesium, oxygen, and silicon - many of them are metals or semiconductors. This is important for generating magnetic
fields on these planets," said Oganov.

A more powerful magnetic field means more powerful protection from cosmic radiation, and consequently more favourable conditions for living organisms.

Researchers predicted new magnesium and silicon oxides that do not fit in with the rules of classical chemistry - SiO, SiO3, and MgO3, in addition to the oxides MgO2 and Mg3O2 previously predicted by Oganov at lower pressures.

The computer model also enabled the researchers to determine the decomposition reactions that MgSiO3 undergoes at the ultra-high pressures on super-Earths - post-perovskite.

"This affects the boundaries of the layers in the mantle and their dynamics. For example, an exothermic phase change speeds up the convection of the mantle and the heat transfer
within the planet, and an endothermic phase change slows them down," said Oganov.

In endothermic change, a possible scenario could be the disintegration of a planet into several independently convecting layers, he said.

The fact that the Earth's continents are in constant motion, "floating" on the surface of the mantle, is what gives volcanism and a breathable atmosphere.

If continental drift were to stop, it could have disastrous consequences for the climate, researchers said.

The study was published in the journal Scientific Reports.