Exoplanet K2-18b ‘may be teeming with life’

There is a 99.7 per cent certainty that the world has at least one gas in its atmosphere that, on Earth, is produced by living things.

An artist's impression shows the K2-18b super-Earth, where astronomers say they have found the strongest yet ’hints’ of life outside the solar system. Picture: University of Cambridge / AFP

A Cambridge astrophysicist has hailed an “astounding” leap forward in the quest to find extraterrestrial life after studying a planet whose atmosphere seems to contain gas that, on Earth, is uniquely produced by living organisms.

Nikku Madhusudhan of the university’s Institute of Astronomy used data from the James Webb Space Telescope (JWST) to declare that K2-18b – a water-covered planet orbiting a star 124 light years away – could be “teeming” with algae-like microbes.

The JWST detected with 99.7 per cent certainty that one or both of the gases dimethyl sulphide (DMS) and dimethyl disulphide (DMDS), compounds made up of carbon, hydrogen and sulphur, are present in concentrations of at least ten parts per million in the planet’s atmosphere. “Given everything we know about this planet, a hycean world with an ocean that is teeming with life is the scenario that best fits the data we have,” said Dr Madhusudhan, lead author of the study, published in The Astrophysical Journal Letters.

The word “hycean” is a combination of the terms “hydrogen” and “ocean”, coined to describe a planet like K2-18b, which is thought to have a hydrogen-rich atmosphere and is entirely covered in water. At 124 light years away it would take 187,000 years to travel there using the fastest spacecraft ever built, the Parker Solar Probe.

Scientists have sounded a note of caution, however, and have stopped short of declaring that they have certainly discovered alien life.

The data took 12 months to analyse and Dr Madhusudhan stressed that another 16-24 hours of observations with the JWST would be needed to boost the confidence levels for the detection of the DMS gases up from a 3-sigma level, a certainty of 99.7 per cent, to the gold standard 5-sigma level, a certainty of 99.99994 per cent, required to make a definitive declaration.

Further theoretical work, to conceive of any non-living process that could explain the presence of the gas, is continuing. Recent studies have suggested DMS can be present in deep space in interstellar gases and even comets.

Michael Steinke, an expert in DMS from the University of Essex, who was not involved in the study, said it was important to consider recent studies suggesting that the gas could potentially be produced in space by “abiotic” means without life.

But Dr Steinke added: “I’m excited to read the paper and see whether there might be life similar to Earth on another planet.”

The Times