An ocean world teeming with alien life may exist 124 light years away from Earth, a study by Cambridge University has hinted.
The exoplanet K2-18b, which exists in the constellation Leo, appears to have an atmosphere containing huge quantities of dimethyl sulfide, a chemical only produced by living organisms such as marine phytoplankton.
Quantities of the chemical are so great that they represent 20 times the biological activity of Earth. The molecule vanishes fairly quickly, suggesting something is continuing to produce it.
Astrophysicists at Cambridge University have described the findings as a “huge, transformational moment” and the strongest hint yet that life exists elsewhere in the universe.
Prof Nikku Madhusudhan, from Cambridge’s Institute of Astronomy, said: “There is no mechanism that can explain what we are seeing without life.
“Given everything we know about this planet, a world with an ocean that is teeming with life is the scenario that best fits the data we have.
He added: “What we are seeing right now are the first hints of an alien world that is possibly inhabited, and this is a revolutionary moment.”
K2-18b is about 2.6 times the size of Earth and exists in the so-called Goldilocks Zone of its star, where conditions are neither too hot nor too cold for life.
It is believed to be a Hycean world, with a huge liquid water ocean under a hydrogen-rich atmosphere, with a temperature slightly warmer than Earth.
Earlier observations had identified methane and carbon dioxide in the atmosphere of K2-18b, which can also be signs of life, but both chemicals are also produced by natural processes, such as volcanic activity.
Scientists asked for the James Webb Space Telescope to be trained on the planet, specifically looking for biomarkers.
They said they were “shocked” when the chemical signal appeared and have spent the last year trying to disprove the finding and “make the signal go away”. The chemical could also be dimethyl disulfide, also a sign of life, which looks similar.
Prof Madhusudhan added: “We have spent an enormous amount of time… trying all sorts of things to kill the signal.
He added: “To be very frank, it was astounding. It’s a shock to the system. I don’t want to be too bullish, but I think frankly this is the closest we have come to a feature that we can attribute to life.”
Subhajit Sarkar, of Cardiff University, a co-author of the study, said: “The inference of these biosignature molecules poses profound questions concerning the processes that might be producing them.”
Prof Madhusudhan said: “This could be the tipping point, where suddenly the fundamental question of whether we’re alone in the universe is one we’re capable of answering.”
Dr Ian Whittaker, a space physics specialist from Nottingham Trent University, said: “This study is rigorous… however, just because these molecules are present and the exoplanet might be ‘Hycean’, i.e. having the conditions for liquid water and a hydrogen atmosphere, does not necessarily mean life has or can form on the planet.”
