Scientists find ‘strongest evidence’ yet of life beyond our solar system

Scientists using NASA’s James Webb Space Telescope have detected what they describe as the strongest signs yet of possible extraterrestrial life, finding chemical signatures in the atmosphere of an exoplanet that on Earth are only produced by living organisms.

The two gases — dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) — were identified in the atmosphere of K2-18 b, a planet located about 124 light years away in the constellation Leo.

“This is a transformational moment in the search for life beyond the solar system, where we have demonstrated that it is possible to detect biosignatures in potentially habitable planets with current facilities. We have entered the era of observational astrobiology,” news agency Reuters quoted astrophysicist Nikku Madhusudhan of Cambridge University’s Institute of Astronomy, who led the study published in The Astrophysical Journal Letters.

K2-18 b is significantly larger than Earth — 8.6 times more massive with a diameter about 2.6 times larger — and orbits in the “habitable zone” of its star, where liquid water could exist on a planetary surface.

The findings represent a potential breakthrough in the search for extraterrestrial life, which has traditionally focused on rocky planets similar to Earth. K2-18 b represents a different possibility — what scientists call a “Hycean world.”

Proposed by Madhusudhan and his team in 2021, Hycean worlds are a subset of sub-Neptune planets that possess a hydrogen-rich atmosphere above a possible water ocean layer. These worlds may be more suitable for certain detection methods than rocky planets.

“The only scenario that currently explains all the data obtained so far from JWST, including the past and present observations, is one where K2-18 b is a Hycean world teeming with life,” Madhusudhan said. “However, we need to be open and continue exploring other scenarios.”

In the paper, they write that “robustly establishing both the veracity of the present findings and their possible association with life on K2-18 b needs a dedicated community effort in multiple directions—observational, theoretical, and experimental.”

Scientists emphasise these findings do not confirm the discovery of actual living organisms but rather a possible biosignature — an indicator of biological processes.

The gases were detected at atmospheric concentrations of more than 10 parts per million by volume. “For reference, this is thousands of times higher than their concentrations in the Earth’s atmosphere, and cannot be explained without biological activity based on existing knowledge,” Madhusudhan explained, according to Reuters.

The detection stands at a 99.7% confidence level, meaning there remains a 0.3% chance of the observation being a statistical fluke. For formal classification as a scientific discovery, the observations must reach a “five-sigma” level, or a 0.00006% probability of being chance.

“It’s important that we’re deeply sceptical of our own results, because it’s only by testing and testing again that we will be able to reach the point where we’re confident in them. That’s how science has to work,” Madhusudhan cautioned.

Further observations are needed to strengthen the evidence. “First we need to repeat the observations two to three times to make sure the signal we are seeing is robust and to increase the detection significance,” said Madhusudhan.

Scientists must also rule out non-biological explanations for the presence of these gases.

If confirmed, the findings would suggest K2-18 b could host microbial life similar to marine phytoplankton on Earth. The discovery marks a significant advancement in humanity’s quest to answer one of its oldest questions: Are we alone in the universe?