A distant exoplanet outside our solar system may be teeming with life, scientists said, after detecting chemical compounds in its atmosphere that — on Earth — are only living organisms produced.
Using data from NASA’s James Webb Space Telescope, a team led by researchers at the University of Cambridge identified molecules in the atmosphere of exoplanet K2-18b that strongly suggest biological activity. The findings, published in The Astrophysical Journal Letters, include the detection of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) — gases that, on Earth, are mainly produced by marine phytoplankton and other microorganisms.
“These molecules are among the most promising biosignatures we’ve ever observed beyond our solar system,” said lead researcher Nikku Madhusudhan from Cambridge’s Institute of Astronomy.
Exoplanet K2-18b is 124 Light-Years Away
K2-18b, located 124 light-years away in the constellation Leo, orbits a red dwarf star in the so-called “habitable zone” — a region where conditions may allow liquid water to exist. The planet is more than twice the size of Earth and nearly nine times as massive, with scientists theorizing an ocean covered it. This has led researchers to classify it as a potential “Hycean world,” or a hydrogen-rich ocean planet.
Previous observations had already detected methane and carbon dioxide in K2-18b’s atmosphere, marking the first time carbon-based molecules were found on an exoplanet within the habitable zone.
Now, new data analyzed by the team revealed concentrations of DMS and DMDS estimated at over 10 parts per million — thousands of times stronger than on Earth, where they typically appear at levels below one part per billion.
“Earlier theoretical work had predicted that high levels of sulfur-based gases like DMS and DMDS are possible on Hycean worlds,” Madhusudhan said. “Now we’ve observed it, and the results match what we anticipated. An ocean world filled with life best fits the data.”
Still, he urged caution, emphasizing the need for further observations to rule out the possibility that these chemicals are the result of unknown non-biological processes.
“It’s exciting, but we have to be careful. We need more data,” Madhusudhan said.
‘Three-Sigma’ Significance
JWST’s Mid-Infrared Instrument (MIRI) confirmed the signals, providing independent evidence from previous observations made using other instruments. The research team, including scientists from NASA and the Space Telescope Science Institute in Baltimore, is calling for follow-up studies to reach the statistical threshold required for a scientific discovery.
The current results reach “three-sigma” significance — meaning there’s a 0.3% chance the detection is due to random variation. Scientists typically require a five-sigma threshold, with a probability of less than 0.00006%, to formally declare a discovery.
Between 16 and 24 hours of additional observation time with JWST could be enough to reach that level, researchers said.
“We may look back and realize this was the moment when the idea of a living universe became within reach,” Madhusudhan said. “This could be a tipping point.”
To analyze exoplanet atmospheres, astronomers study light from a star as a planet passes in front of it — a process known as a transit. Some of the starlight passes through the planet’s atmosphere, leaving chemical fingerprints that telescopes like JWST can detect and decode.
K2-18b’s short orbit means its year lasts just 33 Earth days. Despite its proximity to its star, scientists said its temperature is similar to Earth’s.
In a separate discovery last month, scientists found long organic molecules in ancient Martian rock, fueling speculation that life may once have existed on the Red Planet.
Key Facts: Planet K2-18b
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Discovered: 2015
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Host Star: Red dwarf K2-18
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Location: Constellation Leo
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Mass: 8.6 times Earth’s
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Distance from Earth: 124 light-years
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Orbital Period: 33 Earth days
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