Have we just glimpsed life beyond earth?

Mankind’s search for extra-terrestrial life may have reached a turning point with ‘the strongest signs yet of possible life beyond our solar system’ being detected. In ‘a potential landmark discovery’, scientists using the James Webb Space Telescope (JWST) have detected in an alien planet’s atmosphere the chemical fingerprints of gases that on Earth are produced only by biological processes. The two gases - dimethyl sulphide, or DMS, and dimethyl disulphide, or DMDS - involved in observations of the planet named K2-18 b are generated on Earth by living organisms, primarily microbial life such as marine phytoplankton - 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.

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. "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. There are various efforts underway searching for signs of life in our solar system, including various claims of environments that might be conducive to life in places like Mars, Venus and various icy moons, he noted.

K2-18 b 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, 9.5tn km. One other planet also has been identified orbiting this star.

About 5,800 planets beyond our solar system, called exoplanets, have been discovered since the 1990s. Scientists have hypothesised 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 JWST, launched in 2021 and became operational in 2022, had identified methane and carbon dioxide in K2-18 b’s atmosphere, the first time that carbon-based molecules were discovered in the atmosphere of an exoplanet in a star’s habitable zone.

"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,” he said while stating that the baseline assumption is of simple microbial life. DMS and DMDS, both from the same chemical family, have been predicted as important exoplanet biosignatures. JWST 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.

Scientists not involved in the study counselled circumspection. "The rich data from K2-18 b make it a tantalising world,” said Christopher Glein, principal scientist at the Space Science Division of the Southwest Research Institute in Texas. "These latest data are a valuable contribution to our understanding. Yet, we must be very careful to test the data as thoroughly as possible.”