Astronomers say they've spotted a possible sign of life in the atmosphere of K2-18b, an exoplanet 124 light-years away, using NASA's James Webb Space Telescope.

As detailed in a new paper published in the journal Astrophysical Journal Letters, the international team of researchers led by University of Cambridge astrophysicist Nikku Madhusudhan says they've detected the molecule dimethyl sulfide (DMS) in the planet's atmosphere, which here on Earth — at least as far as we know — is only produced by living organisms.

The team also suggests that it's possible that K2-18b may be a "Hycean" planet, a portmanteau of the words "hydrogen" and "ocean." It's located in its parent red dwarf star system's habitable zone, which means that the conditions could allow liquid water to exist on its surface.

But, as always, extraordinary claims require extraordinary evidence. For one, there's no guarantee that DMS is the result of biological activity; it could be present in the exoplanet's atmosphere for other reasons.

"It's pretty hard to be sure that a chemical that we associate with life can ONLY be made by living things," science communicator and TV personality Joe Hanson wrote in a Bluesky post. "Chemistry is pretty weird, and the galaxy is a very big petri dish."

And to their credit, the researchers themselves were careful — in some ways — about making sweeping claims about having found extraterrestrial life.

"It is in no one’s interest to claim prematurely that we have detected life," Madhusudhan told reporters.

However, he still called it a "revolutionary moment," claiming that it's the "first time humanity has seen potential biosignatures on a habitable planet."

"Either we are looking at a new chemical process that we haven’t seen before... or we’re witnessing the first signs of biological activity outside of Earth," coauthor and Space Telescope Science Institute postdoctoral researcher Mans Holmberg added.

On Earth, marine algae and other living organisms are known to produce dimethyl sulfide, which can eventually reach the air and give the sea a distinctive odor, as the NYT points out.

According to the researchers, K2-18b may be teeming with the stuff, at concentrations thousands of times higher than on Earth, hinting at the possibility of oceans brimming with life.

But while it's a tempting conclusion to draw, experts remain highly skeptical.

"It’s not nothing," Johns Hopkins University planetary scientist Stephen Schmidt, who was not involved in the research, told the NYT. "It’s a hint. But we cannot conclude it’s habitable yet."

"Not yet a biosignature, but a timely prompt to sharpen our methods and expectations," concluded astrophysicist Sara Seager, who was also not involved, told the Washington Post.

"There’s never going to be one biosignature where everyone says, yes, we all agree, definitely life," University of Cambridge biologist Emily Mitchell added. "Any one signature is always going to be debated."

"Unless we see ET waving at us, it’s not going to be a smoking gun," Southwest Research Institute in San Antonio planetary scientist Christopher Glein told the NYT.

It's nonetheless an exciting development, highlighting the cutting-edge observations NASA's JWST has enabled. And the number of potentially habitable exoplanets keeps growing.

Despite broad skepticism, the ongoing conversation surrounding the possibility of life on K2-18b is ultimately a positive thing, Hanson argued.

"People who are not part of this research team are very much more skeptical of these claims than the people who did the research," he wrote in a follow-up post on Bluesky. "That's not necessarily a glaring red flag, it's actually how science should work!"

More on habitability: Scientists Intrigued by Nearby Planet That Could Potentially Support Life


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