‘Are we ready for this?’: Wknd interviews the astrophysicist who captured signs of life on a distant planet
At 45, Nikku Madhusudhan has made the discovery of a lifetime. How did he know where to look? What else could these gas signatures be? An exclusive interview.
Walking home from his University of Cambridge office late at night, Nikku Madhusudhan would often look at the sky and wonder whether we were really alone in the universe.
The professor of astrophysics and exoplanetary science had always been fascinated by how the world works. As a young man, he studied geotechnical engineering at the Indian Institute of Technology at Banaras Hindu University (IIT-BHU). He then earned a Master’s researching electromagnetic properties of meta-materials at the Massachusetts Institute of Technology (MIT). This was followed by a PhD in astrophysics at MIT, where he developed a novel method for inferring the atmospheric properties of exoplanets (planets outside our solar system). He took on postdoctoral positions in astrophysics at MIT, Princeton and Yale.
By 2013, he was a lecturer at Cambridge, and exoplanets were becoming his world.
Then, in 2021 the James Webb Space Telescope was launched. Like everyone in his field, he knew, even as NASA was building it, that JWST would be a game-changer. Installed just beyond Moon’s orbit, about five light seconds away, its infrared sensors and giant mirrors look through interstellar gas and dust, to peer deeper into space than mankind has ever been able to do.
As the top scientists in his field booked slots with JWST, Madhusudhan put in his bid too. His turn came in 2023, in the first year of JWST’s operations.
When it did, he knew exactly where he was going to point it, and what he was looking for.
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In the search for life outside Earth, the big question has always been: Where do we look?
Scientists have traditionally focused on rocky planets a certain distance from their sun (mirroring conditions that made life possible on Earth).
As far back as 2021, Madhusudhan and his team at Cambridge were arguing that the search needed to be expanded in a different direction. There is a kind of planet that is wrapped in a hydrogen-rich atmosphere that likely holds a warm ocean. Based on earlier theoretical work, and their own computational models, this was where we would likely find signs of life, they argued.
Madhusudhan even coined a term for this type of body: hycean planet (a portmanteau of hydrogen and ocean). As soon as his time with JWST began, Madhusudhan pointed the telescope towards a body he had always suspected fit the bill: K2-18b, identified by NASA’s Kepler space telescope in 2015.
Twirling 124 light years away, K2-18b is 2.6 times larger than Earth, positioned at a comfortable distance from its red dwarf star. Could the hyper-focused glare of JWST tell them what they needed to know about it?
At first, the team found methane and carbon-dioxide in the planet’s atmosphere. Paired with the lack of ammonia and carbon-monoxide, this suggested K2-18b could be a hycean world. There were also tentative signs of another molecule, dimethyl sulfide (DMS), but the evidence was inconclusive.
In April 2024, the team turned to JWST again. This time, as the data rolled in, Madhusudhan says he felt a jolt of awe. Over the next few months, he and his team tested the data, tested it again, conducted blind analyses. They came away with the same results every time.
JWST had found the confirmed chemical signature of one of two sulphur-based gases — DMS and dimethyl disulfide (DMDS) — in the atmosphere of K2-18b. On Earth, there is only one thing that produces these gases: organic matter (mainly marine life forms such as phytoplankton).
There is no known way to make DMS and DMDS in large quantities without life.
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The Cambridge team’s findings sent ripples around the world, when they were made public last week, via a report in The Astrophysical Journal Letters.
What do they really mean?
These are the strongest signs of life outside Earth that humanity has ever encountered. Whatever discoveries follow (even if they simply involve new ways in which these compounds can form) will lead to a better understanding of how worlds work — and how to narrow the search for life as we probe further.
“For the first time, we can question,” as Madhusudhan puts it, “whether the basic principles of biology are universal.”
Having put the data out there, the 45-year-old says he feels a huge sense of responsibility.
What the data definitely is, is “a step forward in our understanding of life beyond our solar system,” he says. How we interpret it and build on it will be crucial.
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One question that haunts Madhusudhan is a question to cause goosebumps.
Why is there so much DMS and DMDS in K2-18b’s atmosphere?
The concentrations are thousands of times stronger there than they are here on Earth. Where Earth’s atmosphere has DMS and DMDS in quantities of less than one part per billion by volume, the recent findings show a concentration of more than ten parts per million on K2-18b.
Seeing this data beamed in was surreal, Madhusudhan says.
What else could have caused the gases to occur, in such volumes (or in any volumes at all)? He and his team now hope to use JWST to try to answer that question.
They will also look for similar chemical signals on other hycean worlds. “There are about a dozen known planets that could fall in this category. We are observing four,” Madhusudhan says.
What is truly exciting, he adds, is that this shows exactly how far JWST can take the human powers of observation and inference. “This telescope is of course the real hero here. None of this would have been possible without it. It is the new frontier in astrophysics.” Are we ready for the answers it could provide?
“To my mind, it is not a question of whether there is life out there. If there is life on these hycean worlds, we have the capability to find it,” Madhusudhan says. “The real question is: Are we, as a society and scientific community, prepared to encounter life as we do not know it?”
