Using the James Webb Space Telescope, a team of astronomers has found that K2-18 b has carbon-based molecules and could have an ocean of water.
Scientists have discovered methane and carbon dioxide in the atmosphere of K2-18 b, a distant exoplanet that has long piqued the curiosity of astronomers for having the potential to sustain life.
Using data from the James Webb Space Telescope, scientists based at NASA, the Canadian Space Agency and the European Space Agency (ESA) were able to detect the presence of carbon-bearing molecules including methane and carbon dioxide in the atmosphere of the planet that is about 8.6 times the Earth’s mass.
The discovery adds to recent studies that suggested the K2-18 b could be what is known as a Hycean exoplanet – one that has the potential to have a hydrogen-rich atmosphere and a water ocean-covered surface.
The exoplanet was first spotted in 2015 by NASA’s Kepler spacecraft. Insight into its atmospheric properties came from observations using the Hubble Space Telescope, James Webb’s predecessor, which prompted further studies that have since changed our understanding of the system.
These studies include new observations made with Canadian and European instruments aboard the James Webb, such as the ESA’s NRISpec instrument.
“Our findings underscore the importance of considering diverse habitable environments in the search for life elsewhere,” explained Prof Nikku Madhusudhan, an astronomer at the University of Cambridge and lead author of the paper announcing these results, which will be published in The Astrophysical Journal Letters.
“Traditionally, the search for life on exoplanets has focused primarily on smaller rocky planets, but the larger Hycean worlds are significantly more conducive to atmospheric observations.”
These initial Webb observations also provided a possible detection of a molecule called dimethyl sulphide, which on Earth is only produced by life – largely emitted by the vast swathes of phytoplankton that inhabit our oceans.
“Upcoming Webb observations should be able to confirm if [dimethyl sulphide] is indeed present in the atmosphere of K2-18 b at significant levels,” added Madhusudhan.
Even though K2-18 b hosts carbon-bearing molecules and lies in the habitable zone based on the distance from its star, this does not mean it can necessarily support life. Scientists said that the planet’s large size means that its interior likely contains a large mantle of high-pressure ice.
And while Hycean worlds are predicted to have oceans of water, it is possible that the ocean is too hot to be habitable or be liquid.
“Although this kind of planet does not exist in our solar system, sub-Neptunes are the most common type of planet known so far in the galaxy,” explained team member Dr Subhajit Sarkar of Cardiff University.
“We have obtained the most detailed spectrum of a habitable-zone sub-Neptune to date, and this allowed us to work out the molecules that exist in its atmosphere.”
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