In April, the scientific world—and the public—was abuzz with the thrilling news that a distant planet called K2-18b might show signs of life.
Researchers from Cambridge had analyzed data from NASA’s powerful James Webb Space Telescope and believed they had spotted a molecule in the planet’s atmosphere called dimethyl sulfide.
On Earth, this molecule is only produced by living organisms, especially tiny marine life, so the finding raised hopes that life might exist on a planet 124 light-years away.
But a new study from scientists at the University of Chicago is casting doubt on that possibility.
After reviewing data from multiple telescope observations, they concluded that the evidence is not strong enough to say for sure that dimethyl sulfide—or any life-related molecule—is really there.
The lead author of the new study, Rafael Luque, explained that the signals in the data are simply too “noisy,” meaning they aren’t clear enough to make a solid claim.
In fact, several other molecules could explain what was seen in the data just as well as dimethyl sulfide. This means the evidence isn’t reliable enough to support such a major conclusion.
Understanding why this is so tricky starts with how we observe planets like K2-18b. Because they are so far away and too dim to see directly, astronomers must look for indirect clues.
When the planet passes in front of its star, light from the star filters through the planet’s atmosphere. By analyzing which wavelengths of light are absorbed, scientists can estimate what kinds of molecules might be present.
But here’s the problem: many different molecules can absorb light in similar ways. For example, dimethyl sulfide has a carbon atom bonded to three hydrogen atoms—a structure that’s not unique.
Ethane, a common gas found in planets like Neptune, has a similar signature in the telescope data. So what scientists might think is a sign of life could just as easily be something more ordinary, like ethane.
Michael Zhang, one of the study’s co-authors, said it’s very difficult to tell the difference between these molecules using current data. That’s why scientists are cautious about jumping to conclusions.
Another issue is that the exciting April announcement was based on just one round of observations. When the UChicago team included all available data—from both the Webb and Hubble telescopes—the evidence for dimethyl sulfide became much weaker. This suggests the original claim may have been overstated.
Caroline Piaulet-Ghorayeb, another co-author, emphasized the importance of starting with the simplest explanation. If a known, common molecule like ethane fits the data, there’s no need to assume something exotic like dimethyl sulfide.
The team says they’re not trying to dismiss the excitement of searching for life in the universe—far from it. They just want to make sure the science stays solid. “We are making enormous progress in this field,” said Luque. “We just don’t want that to be overshadowed by premature declarations.”
So for now, while the mystery of K2-18b continues to spark imagination, the search for life beyond Earth remains wide open—and far from settled.
