A giant planet located 124 light years from Earth may be showing the strongest signs yet of possible life beyond our solar system, according to new findings by astronomers using the James Webb Space Telescope.

The planet, known as K2-18 b, lies in the habitable zone of a red dwarf star in the Leo constellation. It’s nearly nine times the mass of Earth and more than twice as large. Detection of the chemicals, dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) would not amount to proof of alien biological activity, but could bring the answer to the question of whether we are alone in the universe much closer.

“This is the strongest evidence to date for biological activity beyond the solar system,” said Professor Nikku Madhusudhan, an astrophysicist at the University of Cambridge who led the study. “We are very cautious. We have to question whether the signal is real and what it truly means.”

The results, published in The Astrophysical Journal Letters, show that the molecules were detected at levels thousands of times higher than those found on Earth. While not definitive proof of life, the findings offer a major step forward in the search for biosignatures on exoplanets. The evidence comes from how starlight passes through the planet’s atmosphere as it crosses in front of its star—a method that allows scientists to analyse the gases present based on how light is absorbed. “The signal came through strong and clear,” said Madhusudhan. “It’s mind-boggling that we’re even able to do this.” However, some scientists remain sceptical. Questions still surround the planet’s true nature—whether it’s a water world, a gas giant, or even a planet with molten oceans. Alternative explanations for the presence of DMS and DMDS include volcanic activity, lightning storms, or comet impacts, though none have yet been shown to fully account for the findings. “Life is one possibility, but it’s just one among many,” said Dr Nora Hänni, a chemist from the University of Berne, who noted that DMS has also been found on icy comets without any known life.

Other experts stress the need for extreme caution. “The burden of proof for such a profound claim must be very, very high,” said Dr Jo Barstow, a planetary scientist at the Open University. “This latest work doesn’t quite reach that threshold.”

K2-18 b first made headlines in 2019 when the Hubble Space Telescope suggested it had water vapour in its atmosphere. Later observations by Madhusudhan’s team revised that interpretation, identifying methane instead—but they argued the data still supports the idea of a habitable world, potentially with a vast ocean beneath a hydrogen-rich atmosphere.

Given the planet’s distance, it’s unlikely scientists will be able to send spacecraft to study it up close. But Madhusudhan said that hasn’t stopped astronomy before. “In this field, it’s never about going there,” he said. “It’s about whether the laws of biology apply universally.”

He added, “Decades from now, we might look back on this moment as the time we first caught a glimpse of the living universe.”