A possibly magma-covered super-Earth with the appearance of an ocean

The types of planets thought to be able to support life may actually be covered in hot magma. Previously thought to have oceans of liquid water, the chemistry of these so-called high sea exoplanets may instead indicate oceans of magma.

Oliver Shortle Researchers from the University of Cambridge used observations from the James Webb Space Telescope (JWST) of the exoplanet K2-18b to reach this conclusion. This world is typically Hycean. This is the name given to a planet with a hydrogen-rich atmosphere above a liquid ocean. These planets also tend to be between Earth and Neptune in size, and the chemicals in their atmospheres suggest the presence of liquid water on their surfaces, making them a prime search for extraterrestrial life. It has become a target.

But recent models of K2-18b's climate suggest it may be hotter than previously thought, hot enough to cause oceans of water to boil away long ago. “From a theoretical perspective regarding the situation here on Earth, it's like the ground is moving beneath our feet,” Schotle says.

The researchers investigated how it would affect Earth's atmospheric chemistry if these oceans were made of magma instead of water. This would be consistent with the expected high temperatures. They found this to be consistent with his JWST observations as well as water bodies.

“These two fundamentally different regimes are very similar,” Schotle says. “Detecting habitable conditions for super-Earths and sub-Neptune-sized planets will be more complex than we expected.”

This means that we probably need more detailed data to tell the difference between a potentially habitable world with oceans of water and a world of burning, inhospitable magma. For K2-18b, Schotle said his additional JWST observations over the next few years should resolve this issue. And when it comes to other Heim worlds, we may need to develop new ideas for how to find liquid water.