WASHINGTON: In a potential landmark discovery, scientists using the James Webb Space Telescope have obtained what they call the strongest signs yet of possible life beyond our solar system.

The researchers have detected the chemical fingerprints of gases in an alien planet’s atmosphere that are produced only by biological processes on Earth.

The two gases - dimethyl sulfide, or DMS, and dimethyl disulfide, or DMDS - involved in Webb’s observations of the planet named ‘K2-18b’ are generated by living organisms, primarily microbial life such as marine algae.

This suggests the planet may be teeming with microbial life, the researchers said. They stressed, however, that they are not announcing the discovery of actual living organisms, but rather a possible biosignature - an indicator of a biological process - and that the findings should be viewed cautiously, with more observations needed.

Nonetheless, these are the first hints of an alien world that is possibly inhabited, said astrophysicist Nikku Madhusudhan of the University of Cambridge’s Institute of Astronomy, lead author of the study published in the Astrophysical Journal Letters.

Data from James Webb telescope finds evidence of chemicals only produced by living organisms on ‘K2-18b’, a planet 8.6 times the size of Earth

“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,” Madhusudhan said.

Asked about possible multicellular organisms or even intelligent life, Madhusudhan said, “We won’t be able to answer this question at this stage. The baseline assumption is of simple microbial life.”

‘K2-18b’ is 8.6 times as massive as Earth and has a diameter about 2.6 times as large as our planet.

It orbits in the “habitable zone” - a distance where liquid water, a key ingredient for life, can exist on a planetary surface - around a red dwarf star smaller and less luminous than our sun, located about 124 light-years from Earth in the constellation Leo.

A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km). One other planet also has been identified orbiting this star.

Exoplanets

About 5,800 planets beyond our solar system, called exoplanets, have been discovered since the 1990s. Scientists have hypothesized the existence of exoplanets called ‘hycean worlds’ - covered by a liquid water ocean habitable by microorganisms and with a hydrogen-rich atmosphere.

Earlier observations by Webb, which was launched in 2021 and became operational in 2022, had identified methane and carbon dioxide in K2-18b’s atmosphere, the first time that carbon-based molecules were discovered in the atmosphere of an exoplanet in a star’s habitable zone.

DMS and DMDS, both from the same chemical family, have been predicted as important exoplanet biosignatures. Webb found that one or the other, or possibly both, were present in the planet’s atmosphere at a 99.7% confidence level, meaning there is still a 0.3% chance of the observation being a statistical fluke.

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 said.

But scientists not involved in the study have counseled circumspection.

To ascertain the chemical composition of an exoplanet’s atmosphere, astronomers analyze the light from its host star as the planet passes in front of it from the perspective of Earth, called the transit method.

As the planet transits, Webb can detect a decrease in stellar brightness, and a small fraction of starlight passes through the planetary atmosphere before being detected by the telescope. This lets scientists determine the constituent gases of the planet’s atmosphere.

The ‘Holy Grail’ of exoplanet science, Madhusudhan said, is to find evidence of life on an Earth-like planet beyond our solar system. He said that our species for thousands of years has wondered “are we alone” in the universe, and now might be within just a few years of detecting possible alien life on a hycean world.

Published in Dawn, April 18th, 2025