Scientists have now figured out that 95 per cent of water present on any exoplanet may be trapped deep inside the planet’s iron core, making it more potentially habitable.
“It is only in recent years that we have begun to realize that planets are more complex than we had thought. Planets are much more water-abundant than previously assumed,” said Caroline Dorn, professor of exoplanets at ETH Zurich in Switzerland, in a statement.
Initially, they are made of hot worlds of oceans of molten magma which have not yet cooled. After cooling, they form a solid mantle of silicate bedrock.
In such magma oceans, water dissolves easily, unlike carbon dioxide, which outgasses and rises in the atmosphere.
Dorn, along with Haiyang Luo and Jie Deng from Princeton University, investigated how the water gets distributed between the silicates and the iron.
Explaining the results of the study, Dorn said, “The iron core takes time to develop. A large share of the iron is initially contained in the hot magma soup in the form of droplets.”
Here’s how water enters the iron core of rocky planets
The water then combines with the iron droplets and carries them to the core. “The iron droplets behave like a lift that is conveyed downward by the water,” Dorn said.
“This is one of the key results of our study. The larger the planet and the greater its mass, the more the water tends to go with the iron droplets and become integrated into the core. Under certain circumstances, iron can absorb up to 70 times more water than silicates. However, owing to the enormous pressure at the core, the water no longer takes the form of H2O molecules but is present in hydrogen and oxygen,” Dorn said.
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The scientists used a computer model to understand how water reacts with molten magma on a young planet and found that much of the water, even on super-earth, can end up in its interior.
“The larger the planet and the greater its mass, the more the water tends to go with the iron droplets and become integrated into the core,” Dorn said.
“Under certain circumstances, iron can absorb up to 70 times more water than silicates. However, owing to the enormous pressure at the core, the water no longer takes the form of H20 molecules but is present in hydrogen and oxygen. So if we find water in a planet’s atmosphere, there is probably a great deal more in its interior,” she explained.
(With inputs from agencies)