Recent reports of the James Webb Space Telescope (JWST) detecting signs of life on a distant planet outside the solar system are unfortunately somewhat premature. This is evident from research by scientists at the University of California Riverside (UCR).
While this will disappoint all of us who are eager for confirmation of extraterrestrial life, it does not mean that the JWST will not find traces of life in the atmosphere of an extrasolar planet, or ‘exoplanet’, in the future.
The recent excitement surrounding the possible detection of life signs on an exoplanet began in 2023 when the JWST discovered potential “biosignature” elements in the atmosphere of the exoplanet K2-18 b, a super-Earth located about 120 light-years from Earth.
While many exoplanets are extreme, violent, or at least “alien” in nature—whether they are destroyed by the intense radiation of their stars, lack a solid surface, or are frozen relics at the edge of their galaxy—K2-18 b a seductive experience. target in the search for life, because it looks quite similar to our planet.
Related: James Webb Space Telescope predicts clouds of molten rock on this blisteringly hot exoplanet
An Earth-like ocean world
K2-18 b is two to three times as wide as Earth and has 8.6 times the mass of our planet. It is also in its star’s habitable zone, a region that is neither too hot nor too cold to support liquid water. So the exoplanet is theorized to be an oceanic or ‘hycean’ world, full of liquid water – an essential ingredient for life as we know it. However, unlike Earth, this exoplanet’s atmosphere appears to be composed mainly of hydrogen and not nitrogen.
“This planet receives almost the same amount of solar radiation as Earth. And if the atmosphere is removed as a factor, K2-18 b has a temperature close to that of Earth, which is also an ideal situation to find life,” says team member and UCR project scientist Shang-Min Tsai said in a statement.
The main conclusion from the 2023 study of K2-18 b, carried out by scientists from the University of Cambridge using the James Webb Space Telescope, was the discovery of carbon dioxide and methane. These molecules were detected without traces of ammonia, indicating that this should indeed be a Hycean world with a vast ocean under a hydrogen-rich atmosphere. But there was also a hint of something else: something very exciting.
“What was the icing on the cake, in terms of the search for life, is that last year these researchers reported a preliminary detection of dimethyl sulfide, or DMS, in that planet’s atmosphere, which is produced by ocean phytoplankton on Earth,” said Tsai. That means if DMS builds up to detectable levels, there must be something on K2-18 b, possibly a life form, that is producing it 20 times faster than on Earth.
There’s icing on the super-earth cake, but can we eat it?
However, as the detection of DMS was inconclusive, even the team leader of the study, scientist Nikku Madhusudhan of the University of Cambridge, urged caution regarding the discovery of DMS. He said future JWST observations would be needed to confirm its presence in K2-18 b’s atmosphere — but not everyone got the memo.
However, the unclear nature of the DMS detection also prompted the UCR team to follow up on the detection.
“The DMS signal from the JWST was not very strong and only showed up in certain ways when analyzing the data,” Tsai said. “We wanted to know if we could be sure of what seemed like a hint about DMS.”
What this second team discovered using computer models that took into account hydrogen-based atmospheres and for the physics and chemistry of DMS was that the original data was unlikely to indicate the detection of DMS. “The signal overlaps strongly with methane, and we believe that picking up DMS from methane is beyond the capabilities of this instrument,” Tsai said.
That means the JWST will have to look at the world with instruments other than the NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near-Infrared Spectrograph) used to conduct the first study to detect evidence of DMS . Fortunately, Madhusudhan’s team continues to observe K2–18 b with the JWST’s other primary instrument, the MIRI (Mid-Infrared Instrument), as researchers gather more information about the exoplanet’s environmental conditions.
“The best biosignatures on an exoplanet can differ significantly from the biosignatures most commonly encountered on Earth today,” says team leader and UCR astrobiologist Eddie Schwieterman. “On a planet with a hydrogen-rich atmosphere, we are more likely to find DMS made by life rather than oxygen made by plants and bacteria, as on Earth.”
Is this slight disappointment a setback for scientists searching the cosmos for signs of life? No coincidence – nor does it overshadow the importance of the initial research as a step forward in our understanding of Hycean worlds, some of the most promising targets in that quest.
“Why do we continue to explore the cosmos for signs of life?” Tsai asked rhetorically. “Imagine you’re camping in Joshua Tree at night and you hear something. Your instinct is to shine a light to see what is out there. In a sense, that is also what we do.’
The new study discussing these findings was published May 2 in The Astrophysical Journal Letters.
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