A new study carried out by scientists at UC Berkeley suggests that super-Earths up to five times the size of the Earth can have a powerful magnetic field produced by slow churning of molten rocks (magma) under or at their surface.
The new findings also suggests that our planet in its early years most likely had a magma-produced magnetic field, along with the magnetic field that still exists today and is generated in the liquid-iron outer core.
A magnetic field plays a vital role in protecting the atmosphere of a planet from being blown away by powerful stellar winds. The Earth's magnetic field is generated in its liquid-iron outer core. On gas giant Jupiter, it is generated due to the convection of liquid metallic hydrogen. Magnetic fields on Uranus and Neptune are believed to arise in their ice layers.
"This is a new regime for the generation of planetary magnetic fields," said Burkhard Militzer, a UC Berkeley professor of earth and planetary science.
"This is far in the future, but if someone makes an observation of an exoplanet and they find a magnetic field, that may be an indication that there is a magma ocean, even if they cannot see this directly," Militzer said.
In recent years, astronomers have discovered several super-Earths around stars in the universe. These super-Earths are characterised by their large size and mass. Scientists believe the interior (the mantle) of these super-Earths must be liquid and convecting for a few billion years after their formation. Moreover, the slowly boiling magma can generate a magnetic field only if it conducts electricity.
Until now, scientist had no idea whether this was true.
In the new study, scientists used the advanced atomic-scale computer simulation models of minerals to calculate the electrical conductivity of magnesia (magnesium oxide), a silicon-magnesium-oxide (post-perovskite), and quartz (silicon dioxide). All of these compounds are found on Earth and the moon. They are also likely present in the rocks on other planets of our solar system.
Scientists carried out detailed calculations for three silicates and found that all of them start conducting electricity when they change from solid to liquid at high pressures and temperatures.
When these results were fed in the models for Earth's interior, they showed that the rocks on Earth are adequately conducting to maintain a magnetic field. It happens as the disorganised structure of the molten rocks helps the electrons to conduct electricity.
François Soubiran, a former UC Berkeley postdoctoral fellow, who was involved in the study, said that the planets that complete a rotation on their axis in a period of two or more days would produce an Earth-like magnetic field. However, a slower rotation could generate a more disorganised magnetic field which would be difficult to detect from afar.
The detailed findings of the study are published in journal Nature Communications.
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