A group of Cambridge scientists has uncovered the “strongest evidence yet” of biological activity on an exoplanet over 120 light years from Earth.

Led by Professor Nikku Madhusudhan from the Institute of Astronomy, the team used data collected from NASA’s James Webb Space Telescope (JWST) to detect traces of dimethyl sulphide (DMS) in the atmosphere of K2-18b. On Earth, this molecule is produced only by living organisms such as marine phytoplankton.

“This is the strongest evidence yet that there is possibly life out there,” Madhusudhan said. “If we confirm that there is life on K2-18b, it should basically confirm that life is very common in the galaxy… Decades from now, we may look back at this point in time and recognise it was when the living universe came within reach.”

Despite this, the team is quick to state that the findings are still far from conclusive. The presence of the DMS molecule was detected with a statistical confidence of three sigma, corresponding to approximately a 99.7% certainty. To be definitive, a scientific discovery typically requires a five-sigma result, or 99.99994% confidence.

The exoplanet has been deemed a “sub-Neptune,” meaning it is larger than Earth but smaller than Neptune, one of the most common classes of planets in the galaxy. The planet is situated in the habitable zone of a cool, red dwarf star and is believed to be covered in a vast ocean.

In 2023, Varsity reported on the team’s discovery of high concentrations of methane and carbon dioxide in the exoplanet’s atmosphere, which are typically associated with habitable environments. Notably, ammonia appeared to be absent in the atmosphere, leading some researchers to theorise that it may be absorbed by a large body of liquid water on the planet.

Despite some uncertainty, Madhusudhan believes that with additional JWST observations scheduled over the next two years, the confidence level could be pushed beyond five sigma. “So we want to be really, really thorough,” he stated. “There’s still a 0.3% chance this is a statistical fluke.”

Professor Catherine Heymans, Scotland’s Astronomer Royal, stated: “Even with perfect data we can’t say for sure this is of a biological origin… We don’t know what other geological activity could be happening on this planet.”

The Cambridge team is now working with chemists and planetary scientists to determine whether DMS and its molecular cousin, dimethyl disulphide (DMDS), can be produced through non-biological processes.