In a revelation that could change our place in the universe forever, British-led astronomers have uncovered what could be the strongest evidence yet of life outside our solar system – though they are urging caution before popping the champagne.
Experts at the University of Cambridge, working with NASA’s James Webb Space Telescope (JWST), have detected the chemical fingerprints of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS) in the atmosphere of a distant planet named K2-18b, located a staggering 124 light years away in the constellation Leo.
On Earth, these two molecules are only produced by life – specifically microbial life such as marine phytoplankton. Now, they’ve been spotted on a planet that sits comfortably in the “Goldilocks zone” – not too hot, not too cold – where conditions might be just right for life to exist.
Could it be aliens? The answer isn’t clear – yet.
“We didn’t know for sure whether the signal we saw last time was due to DMS, but just the hint of it was exciting enough for us to have another look with JWST using a different instrument,” said Professor Nikku Madhusudhan from Cambridge’s Institute of Astronomy, who led the groundbreaking research.
And now they’ve got it. The new detection, made using JWST’s MIRI (Mid-Infrared Instrument), confirms a strong signal that matches that of life-related chemicals. “This is an independent line of evidence… The signal came through strong and clear,” added Professor Madhusudhan.
But before anyone cries “ET found!”, scientists are keeping their feet firmly on the ground.
The signal has reached a statistical significance of three sigma, meaning there’s a 0.3% chance the finding is a fluke. To reach scientific gold standard status – five sigma – more observations are needed, cutting the chance of coincidence to less than 0.00006%.
“We’re deeply sceptical of our own results,” said Madhusudhan. “That’s how science has to work.”
The team estimates it will take between 16 and 24 hours of additional JWST observation time to confirm the detection and potentially rewrite the history books.
K2-18b is no ordinary planet. At 2.6 times the size of Earth and 8.6 times its mass, it’s classified as a Hycean world – a planet likely covered in oceans beneath a thick, hydrogen-rich atmosphere.
Earlier observations had already identified methane and carbon dioxide – both key ingredients in Earth-like biology – in the planet’s skies. But it was a faint, mysterious signal that hinted at something even more tantalising.
Now, using a different part of the spectrum – mid-infrared rather than near-infrared – that very same signal has shown up again, this time stronger.
“It was an incredible realisation seeing the results emerge and remain consistent throughout the extensive independent analyses and robustness tests,” said co-author Måns Holmberg, from the Space Telescope Science Institute in the US.
The molecules DMS and DMDS – both considered potential biosignatures – appear to exist in astonishingly high quantities on K2-18b. Unlike Earth, where DMS levels sit at below one part per billion, here they could be more than 10 parts per million – thousands of times higher.
Professor Madhusudhan noted: “Earlier theoretical work had predicted that high levels of sulfur-based gases like DMS and DMDS are possible on Hycean worlds… 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.”
Still, scientists caution that the planet could be producing these gases through unknown non-biological processes. The team is now racing to test such scenarios and unravel the mystery.
“The inference of these biosignature molecules poses profound questions concerning the processes that might be producing them,” said co-author Dr Subhajit Sarkar from Cardiff University.
Their findings are published in the journal Astrophysical Journal Letters under the title: ‘New Constraints on DMS and DMDS in the Atmosphere of K2-18b from JWST MIRI.’
The research was supported by a UK Research and Innovation Frontier Research Grant, and forms part of the UK’s ongoing leadership in the search for extraterrestrial life.
“Decades from now, we may look back at this point in time and recognise it was when the living universe came within reach,” said Professor Madhusudhan. “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.”
The James Webb Space Telescope is a joint mission between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA).
For those eager to learn more about these oceanic alien worlds, visit hycean.group.cam.ac.uk.
Source: Cambridge University
