In what may be a landmark moment in the search for extraterrestrial life, a team led by Indian-origin astrophysicist Professor Nikku Madhusudhan from the University of Cambridge has found the strongest hints yet of life on a faraway exoplanet.
Using data from NASA&rsquo;s James Webb Space Telescope (JWST), the team detected chemical fingerprints of dimethyl sulphide (DMS) and/or dimethyl disulphide (DMDS) in the atmosphere of K2-18b&mdash;a planet orbiting a small red star about 124 light-years away in the constellation of Leo.
These molecules are known on Earth to be produced exclusively by living organisms, particularly marine phytoplankton and bacteria. The potential presence of such biosignatures in large quantities has sparked significant excitement within the scientific community, although experts emphasize the need for further confirmation.
&ldquo;This is the strongest evidence yet that there is possibly life out there,&rdquo; said Prof Madhusudhan. &ldquo;I can realistically say that we can confirm this signal within one to two years.&rdquo;
Atmospheric Evidence and Advanced Detection
The study, published in The Astrophysical Journal Letters, is based on observations using JWST&rsquo;s highly sensitive instruments: NIRISS (Near-Infrared Imager and Slitless Spectrograph), NIRSpec (Near-Infrared Spectrograph), and more recently, MIRI (Mid-Infrared Instrument). These tools allow scientists to analyze the chemical composition of an exoplanet&rsquo;s atmosphere by observing the light that passes through it.
Notably, the latest MIRI observations reached a &lsquo;three-sigma&rsquo; level of statistical confidence, meaning there is a 99.7% probability that detection of DMS/DMDS is not a fluke. However, scientists aim to reach the five-sigma level (99.99994%) before officially confirming a discovery.
&ldquo;We want to be really, really thorough, and make more observations, and get the evidence to the level that there is less than a one-in-a-million chance of it being a fluke,&rdquo; Prof Madhusudhan told BBC Radio 4.
Massive Ocean World or Gas Giant?
K2-18b is about 2.6 times the size of Earth and 8.6 times more massive. The research team believes the planet could host a vast liquid ocean&mdash;potentially a habitat for life. The absence of ammonia in the atmosphere supports this theory, as ammonia is known to dissolve in water.
However, alternative interpretations of the data exist. Some scientists suggest K2-18b may instead be a mini gas giant with no surface, or even an ocean of molten rock&mdash;both scenarios that could rule out life. 
&ldquo;Everything we know about planets orbiting other stars comes from the tiny amounts of light that glance off their atmospheres. So, it is an incredibly tenuous signal that we are having to read,&rdquo; cautioned Prof Oliver Shorttle of Cambridge University.
Cautious Optimism 
The excitement around this discovery is tempered by scientific caution. Even if DMS and DMDS are confirmed, they could potentially be formed through unknown geological or chemical processes unrelated to life. &ldquo;Loads of strange things happen in the Universe, and we don&rsquo;t know what other geological activity could be happening on this planet that might produce the molecules,&rdquo; said Prof Catherine Heymans, Scotland&rsquo;s Astronomer Royal.
To address these questions, the Cambridge group is working with other researchers to test whether non-biological processes could account for the observed molecules.
Significance for Humanity
&ldquo;This could be the tipping point,&rdquo; Prof Madhusudhan reflected. &ldquo;Decades from now, we may look back at this point in time and recognize it was when the living universe came within reach.&rdquo;
The potential discovery underscores the importance of continued exploration. Between 16 and 24 hours of follow-up JWST observations may be enough to confirm the signal beyond doubt. Until then, the world watches&mdash;and waits&mdash;for an answer to one of humanity&rsquo;s oldest questions: are we alone in the universe?
(with inputs from IANS)
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April 17, 2025 | 19:04 IST