Astronomers at the University of Cambridge have uncovered new but inconclusive evidence suggesting the potential presence of life on a remote exoplanet orbiting a star far beyond our solar system.
Analysing data from NASA’s James Webb Space Telescope (JWST), researchers identified molecules in the atmosphere of exoplanet K2-18b that, on Earth, are solely produced by simple life forms. This marks the second time such biologically-linked compounds have been detected on the planet, although the latest signals are deemed notably stronger, according to the BBC.
Professor Nikku Madhusudhan, who led the study at Cambridge University’s Institute of Astronomy, expressed cautious optimism.
“This is the strongest evidence yet that there is possibly life out there,” he said. “I can realistically say that we can confirm this signal within one to two years.”
K2-18b, located approximately 700 trillion miles away, is more than twice the size of Earth and orbits a cool red dwarf star. The advanced instrumentation aboard the JWST enables astronomers to analyse a planet’s atmosphere by observing how starlight passes through it, thereby revealing the chemical makeup of the gases present.
The Cambridge team reported the detection of dimethyl sulphide (DMS) and dimethyl disulphide (DMDS)—compounds which, on Earth, are primarily emitted by marine phytoplankton and certain bacteria.
“The estimated concentration of this gas in the atmosphere is thousands of times higher than what we find on Earth,” said Prof Madhusudhan. “So, if the association with life is real, then this planet will be teeming with life.”
He added that confirming life on K2-18b would strongly suggest that life is widespread across the galaxy.
Despite the excitement, researchers caution that more evidence is required. Currently, the detection holds a “three sigma” confidence level, equating to a 99.7% likelihood that the signal is real—still short of the “five sigma” standard (99.99999%) typically needed for scientific confirmation.
Professor Catherine Heymans, Scotland’s Astronomer Royal and a physicist at the University of Edinburgh who is not involved in the study, urged restraint.
“Even with that level of certainty, we still face the question of the gas’s origin,” she told BBC News. “On Earth, it’s produced by microorganisms in the oceans, but even with perfect data, we can’t be sure the source is biological on an alien world. Strange geological processes might be at play that we simply don’t understand.”
The Cambridge researchers share this measured view. They are collaborating with other scientists to test whether these molecules could be produced through non-biological means in laboratory settings.
Alternative theories continue to circulate. One posits that K2-18b harbours a vast ocean of liquid water capable of absorbing ammonia from the atmosphere—a potential indicator of habitability. However, other scientists contend that the absence of ammonia could instead point to a molten rock ocean, rendering the environment inhospitable to life.
Professor Oliver Shorttle of Cambridge University noted the fragility of the data.
“Everything we know about exoplanets comes from minuscule traces of light filtered through their atmospheres,” he said. “It’s an incredibly subtle signal. With K2-18b, the scientific debate is still ongoing—even regarding the planet’s structure.”
Further complicating matters, Dr Nicolas Wogan of NASA’s Ames Research Center has suggested that K2-18b may be a mini gas giant lacking a solid surface, casting further doubt on its ability to sustain life.
Nonetheless, Prof Madhusudhan remains hopeful.
“Decades from now, we may look back at this moment as when the living universe came within reach,” he said. “This could be the tipping point—when we truly began to answer the fundamental question of whether we’re alone in the cosmos.”
The full findings have been published in The Astrophysical Journal Letters.
