The James Webb Space Telescope has detected possible chemical signs of life in the atmosphere of an exoplanet, but researchers warn it's still too early to tell.
Astronomers have identified the most promising evidence yet for a biological clue outside the solar system, but caution is still being exercised. Using data from the James Webb Space Telescope (JWST), a Cambridge University-led study has identified chemical fingerprints of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS) in the atmosphere of the exoplanet K2-18b, which is located in the habitable zone of its star.
On Earth, DMS and DMDS are created exclusively by biological activity, primarily microbial, such as marine plankton. Although an unknown chemical process on K2-18b may be responsible for their appearance, the study findings provide the strongest evidence that life may exist on a planet outside our solar system.
The observations reached a statistical significance level of three sigma, meaning there is a 0.3% chance that they were created by chance. To achieve the status of an accepted scientific discovery, it is necessary to cross the five sigma threshold, which is significant at a chance of less than 0.00006% of occurring by chance. The researchers estimate that an additional 16 to 24 hours of observation with JWST could help them reach the required significance. The results were published inThe Astrophysical Journal Letters.
Previous observations of K2-18b—a star 8.6 times more massive and 2.6 times more massive than Earth, located 124 light-years away in the constellation Leo—had detected for the first time the molecules carbon, methane, and carbon dioxide in its atmosphere. These findings were consistent with the hypothesis that K2-18b is a “Hycean world”: a planet covered by an ocean and under a hydrogen-rich atmosphere.
However, a weaker signal than the first study raised another possibility. “We didn’t know if the signal we detected then was from DMS, but the intriguing clue led us to look at K2-18b again with JWST and a different instrument,” explained Professor Niko Madhusudhan of the Institute of Astronomy in Cambridge, who led the research team.
To determine the composition of the atmospheres of distant stars, astronomers use the transit technique: when a planet passes in front of its parent star, some of the light penetrates through the planet's atmosphere and reaches us with spectral absorption signatures. By analyzing these signatures, it is possible to identify which gases are present in the atmosphere.
The initial detection of DMS was made using JWST’s Near-Infrared Imager and Slitless Spectrograph (NIRISS) and Near-Infrared Spectrograph (NIRSpec), which operate in the 0.8–5 micron range. The new, independent observation was made using JWST’s Mid-Infrared Instrument (MIRI), which operates in the 6–12 micron range. “This is a standalone line of evidence, with no overlap with previous observation ranges,” Madhusudhan emphasized, “and the signal came in strong and clear.”
“That was the moment we realized that the results were stable and successfully passed all of our independent tests,” added Dr. Mons Holmberg of the Space Telescope Science Institute in Baltimore.
DMS and DMDS belong to the same family of molecules, and both are considered potential biosignatures. The two gases exhibit overlapping spectral features in the observable range, but future observations may distinguish them. At estimated concentrations of tens of parts per million, their levels in K2-18b are hundreds to thousands of times higher than those found on Earth (i.e., below our part per billion).
“Previous theoretical work predicted that high levels of sulfur gases like DMS and DMDS would be possible on Hycean worlds,” said Madhusudhan, “and here we see it in reality, consistent with the prediction. Based on everything we know, a Hycean world with a vibrant ocean is the scenario that best fits the data.”
Despite the excitement, the researchers emphasize that caution should be exercised and additional data should be acquired before declaring the discovery of life. It is possible that non-biological chemical processes on K2-18b could explain the presence of DMS and DMDS at the observed levels. To this end, theoretical studies and laboratory experiments are planned to test whether these molecules can be produced under lifeless planetary conditions.
“The hypothesis of the existence of these biosignatures raises profound questions about the processes that might produce them,” said Dr Subhajit Sarkar from Cardiff University. “Our work is the starting point for the investigations needed to confirm and understand these exciting findings,” added Dr Sabavas Constantinopoulos from the Institute of Astronomy, Cambridge.
“It is important that we remain skeptical of our findings, because only through repeated testing can we achieve true confidence in the results,” concluded Madhusudhan.
While he doesn’t claim to have made a definitive discovery, Madhusudhan notes that with powerful tools like JWST and planned future telescopes, humanity is taking another critical step toward answering the central question: Are we alone in the universe? “Decades from now, we may look back and think that this moment was the turning point when the living universe became accessible to understanding,” he said.
The James Webb Space Telescope is a joint project of NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA). The research is supported by a Frontier Research grant from UK Research and Innovation (UKRI).
Learn more about Hycean Worlds
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124 light years from Earth is about 1,698,800 years of flight for the fastest spacecraft ever built.
We will never fly anything at speeds approaching the speed of light.
The vast majority of the universe is physically inaccessible to us forever.
The best proof of the existence of extraterrestrial life is the appearance.
If it weren't for genetic manipulation of the humanoids who lived here 400,000 years ago and additional manipulations, we wouldn't have reached what we are today through normal evolution.
And if that doesn't convince you, write down the size of the crop circles and try to come to the conclusion that humans did it in the dead of night with ropes and wooden planks.
Every day and the new space exploration, and the scientific proofs? For believers only. And this is so that NASA can continue to blow a budget of 66 million shekels per day. And the benefit to humanity? Nothing.
It's true that every now and then another sketch is published telling us that NASA is not only traveling in space but also bringing us some new technological solution. But it's clear that this is a marketing need, because otherwise why spend billions upon billions on space travel that hasn't brought us anything for decades.
It's completely clear why "researchers are warning." The star is at a distance of "we'll never get there" (no distance from Earth is specified) and if we get there in about two thousand years, future researchers will say.. "Wow, the researchers of the third millennium were so careful..."