Large Exoplanet May Have Right Conditions For Life

Artist's impression of K2-18b (via Amanda Smith/University of Cambridge)

An exoplanet more than twice the size of Earth may be habitable, according to astronomers from the University of Cambridge.

K2-18b is the only planet orbiting a star outside our Solar System known to have water and temperatures that could support life.

The orb made headlines last year, when two different teams reported detection of water vapour in its hydrogen-rich atmosphere. The extent of the interior conditions, however, remained unknown.

Until now.

“Water vapour has been detected in the atmospheres of a number of exoplanets but, even if the planet is in the habitable zone, that doesn’t necessarily mean there are habitable conditions on the surface,” lead researcher Nikku Madhusudhan, of Cambridge’s Institute of Astronomy, said in a statement.

“To establish the prospects for habitability,” he continued, “it is important to obtain a unified understanding of the interior and atmospheric conditions on the planet—in particular, whether liquid water can exist beneath the atmosphere.”

Identified in 2015 by NASA’s Kepler spacecraft, K2-18b orbits the red dwarf K2-18, some 124 light years from Earth in the Leo constellation.

It is one of hundreds of super-Earths—planets with a mass between Earth and Neptune—spotted by Kepler; NASA’s new TESS mission is working to uncover hundreds more.

Despite its size, though, K2-18b’s water layer could have the right conditions to support life.

Researchers confirmed the planet’s hydrogen-rich atmosphere contains a “significant” amount of water vapor; levels of other chemicals (methane, ammonia) were lower than expected.

“We wanted to know … how deep the hydrogen goes,” co-author Matthew Nixon, a PhD student at the Institute of Astronomy, said. “While this is a question with multiple solutions, we’ve shown that you don’t need much hydrogen to explain all the observations together.”

Most notably, a number of scenarios allow for an ocean world, with liquid water below the atmosphere at pressures and temperatures similar to those found in Earth’s oceans.

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