Readings from NASA’s James Webb Space Telescope confirm the presence of carbon-based molecules including methane and carbon dioxide in the atmosphere of a distant planet known as K2-18 b — which supports previous suggestions that it might be the kind of ocean-covered world capable of harboring marine life.
K2-18 b, which was first detected in 2015 using data from NASA’s now-retired Kepler space telescope, lies in the habitable zone of a star system that’s about 120 light-years away in the constellation Leo. It’s about 8.6 times as massive as Earth, and astronomers regard it as a sub-Neptune — a type of planet that doesn’t exist in our solar system.
Since its initial detection, astrobiologists have been interested in the world’s potential for habitability. They suspected it might be what’s called a Hycean planet — a type of world that’s massive enough to hold onto a hydrogen-rich atmosphere and a globe-spanning sea. The evidence has been piling up: In 2019, researchers reported the chemical signature of water vapor and clouds in K2-18 b’s atmosphere.
The fact that JWST detected an abundance of methane (CH4) and carbon dioxide (CO2), along with a shortage of ammonia (NH3), is consistent with the atmospheric modeling for Hycean planets.