A possible sign of life on K2-18b? Here’s what it means- and why it's just the beginning

In what a team of researchers claim is our strongest hint yet that we're not alone in the Universe, scientists may have detected dimethyl sulfide — a chemical almost uniquely associated with life on Earth — in the atmosphere of another planet. If the evidence holds up, this would mean that a world more than 100 light-years away hosts a substance that, on Earth, only exists because of plants and microbes.

Before this can be called a discovery, many questions have to be answered first. Scientists must confirm if the signal is real and if it truly indicates the presence of life, confronting lots of possible alternatives along the way. But no matter what they find, these first hints mark a new era in how we search for life beyond the Solar System.

A possible signal
Using the James Webb Space Telescope (JWST), a team of researchers has peered into the atmosphere of a planet called K2-18 b as it passed in front of its star. This technique, called transmission spectroscopy, allows scientists to puzzle out the contents of a planet’s atmosphere by seeing how light gets absorbed by its gases on the way toward us. In this case, the researchers found signatures that appear to be best explained by a chemical called dimethyl sulfide (DMS), or its cousin dimethyl disulfide (DMDS), or possibly both.

Astrobiologists have long had these molecules on their “Most Wanted” lists. On Earth, DMS is only known to exist because of life, with certain plants and marine microbes producing a chemical that breaks down into DMS over time. This makes DMS a remarkably specific sign of life, one that’s much harder to explain any other way.

The discovery of DMS in the atmosphere of K2-18 b would be an extremely tantalizing find. It may even become the strongest sign of life discovered beyond the Solar System, ever. Though telescopes have looked into the atmospheres of faraway planets before, they have never found a substance that, on Earth, is only associated with life.

For K2-18 b in particular, the discovery of DMS would crown an ongoing narrative that the team behind the new results has been championing for years. According to the group, which is led by Nikku Madhusudhan, PhD, at the University of Cambridge, K2-18 b represents a new kind of world: one completely covered in ocean.

The JWST results, if true, could mean those oceans are teeming with life.