Super Earths that seem to have oceans may actually be covered in magma

An illustration of the exoplanet K2-18b based on scientific observations

NASA, ESA, ASC, Joseph Olmsted (STScI)

A type of planet thought to support life may actually be covered in hot magma. The chemical properties of these so-called Hycean exoplanets – previously thought to harbor oceans of liquid water – could instead indicate seas of magma.

Olivier Shortttle from the University of Cambridge and colleagues came to this conclusion using James Webb Space Telescope (JWST) observations of the exoplanet K2-18b. This world is typically Hycean – a name given to planets with a hydrogen-rich atmosphere above a liquid ocean. These planets also tend to be between Earth and Neptune in size, and their atmospheres exhibit chemistry that suggests liquid water exists on the surface, making them prime targets in the hunt for planets. life beyond Earth.

However, recent models of K2-18b's climate indicate that it may be warmer than previously thought, sweltering enough that ocean water may have long since disappeared. “The ground is moving beneath our feet, from a theoretical point of view, in terms of the conditions on this planet,” says Shortttle.

The researchers studied how it would affect the planet's atmospheric chemistry if these oceans were made of magma rather than water, which would be consistent with the predicted warmer temperatures. They found that this matched both the JWST and ocean observations.

“These two radically different diets are very similar,” explains Shortttle. “This makes detecting habitable conditions on a super Earth or planet smaller than Neptune more complicated than we might have hoped.”

This means we probably need more detailed data to differentiate between a potentially habitable world with oceans of water and a hot, inhospitable magma world. For K2-18b, Shortttle says the question should be resolved by additional JWST observations in the coming years. And when it comes to other Hycean worlds, we may need to develop new ideas on how to search for liquid water.

The subjects:

  • exoplanets/
  • James Webb Space Telescope

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