A hint of life across the stars? A distant planet offers an enticing clue
New Delhi, Apr 17: In the boundless black of space, seven hundred trillion miles from Earth, a planet cloaked in mystery may be whispering a cosmic secret: the presence of life. The planet, K2-18b, is no ordinary celestial body. It’s more than twice the size of Earth, orbits a cool red dwarf star, and has long intrigued astronomers as one of the more promising candidates in the search for life beyond our solar system. Now, new findings from a team at the University of Cambridge may have brought that distant dream a little closer to reality. “This is the strongest evidence yet there is possibly life out there,” said Professor Nikku Madhusudhan, lead researcher at Cambridge University’s Institute of Astronomy, in an interview with the BBC. “I can realistically say that we can confirm this signal within one to two years.”
The signal he refers to is the spectral trace of molecules—specifically dimethyl sulphide (DMS) and dimethyl disulphide (DMDS)—in the atmosphere of K2-18b. These are compounds which, on Earth, are produced exclusively by marine phytoplankton and certain bacteria. Their presence, if verified, could mark a historic milestone: the first clear sign of biological activity beyond our pale blue dot.
The discovery, detailed in The Astrophysical Journal Letters, was made using data from NASA’s James Webb Space Telescope (JWST), whose unparalleled precision allows scientists to study the chemical makeup of distant exoplanets by analyzing the starlight that filters through their atmospheres.
What astonished Madhusudhan’s team wasn’t just the presence of these molecules—but the quantity. “The amount we estimate of this gas in the atmosphere is thousands of times higher than what we have on Earth,” he told the BBC. “So, if the association with life is real, then this planet will be teeming with life.”
Still, even amid such tantalizing findings, caution prevails. The detection stands at a “three sigma” level—about 99.7% certainty. In the rigorous realm of science, that’s not enough.
A “five sigma” confidence, or 99.99999%, is the gold standard for declaring a discovery. Eighteen months ago, a prior study by the same team had only reached a “one sigma” threshold, prompting much skepticism at the time.
Even if future data pushes the certainty further, the question of origin remains complex. “Even with that certainty, there is still the question of what is the origin of this gas,” said Professor Catherine Heymans, Scotland’s Astronomer Royal and an astrophysicist at the University of Edinburgh, speaking to the BBC. “Even with perfect data we can’t say for sure that this is of a biological origin on an alien world.”
Indeed, the Cambridge team is well aware of the alternative explanations. They’re now collaborating with other researchers to test whether such molecules could also be produced through non-biological, geological processes. Other scientists, meanwhile, have proposed starkly different visions of K2-18b altogether—some suggest it may be a planet covered not by a global ocean, but by molten rock, or that it’s more akin to a mini gas giant without a solid surface at all. “It is an incredibly tenuous signal that we are having to read, not only for signs of life, but everything else,” said Prof Oliver Shorttle of Cambridge University. As he told the BBC, “with K2-18b, part of the scientific debate is still about the structure of the planet.”
The spirited debate underscores both the power and limitations of JWST’s capabilities. While it allows us to peer deeper into the cosmos than ever before, even its insights are drawn from the faintest glimmers of light—deciphered pixel by pixel from a realm we may never physically reach. Yet, for Madhusudhan, this is more than just an incremental advance in exoplanetary science. It might be the beginning of a profound shift in human understanding. “Decades from now, we may look back at this point in time and recognise it was when the living universe came within reach,” he 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.” For now, the mystery of K2-18b remains unsolved. But with each photon captured, each molecule measured, the cosmos is whispering a little more of its story and we are learning how to listen.
