Recent reports of the James Webb Space Telescope (JWST) detecting signs of life on a distant exoplanet are unfortunately somewhat premature. This is the conclusion of research conducted by scientists from the University of California Riverside (UCR).
Although it will likely disappoint all of us eager to confirm the existence of extraterrestrial life, this does not mean that the James Webb Space Telescope will not find traces of life in the atmosphere of an extrasolar planet, or “exoplanet,” in the future.
Recent excitement over the potential discovery of signs of exoplanet life began in 2023 when the James Webb Space Telescope detected potential “biosignature” elements in the atmosphere of the exoplanet K2-18 b, a super-Earth planet located about 120 light-years from Earth.
Although many exoplanets are extreme, violent, or at least “weird” in nature — whether they experience intense radiation from their stars, lack a solid surface or have icy traces at the edge of their systems — K2-18 b has been a baffling thriller. The goal is to search for life because it is somewhat similar to our planet.
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An oceanic world similar to Earth
K2-18 b is two to three times the width of Earth and has a mass of 8.6 times that of our planet. It is also located in its star's habitable zone, a region that is neither too hot nor too cold to support the presence of liquid water. Hence, the exoplanet is seen as an ocean, or “Hesian” world, filled with liquid water – a vital ingredient for life as we know it. Unlike Earth, this exoplanet's atmosphere appears to be composed primarily of hydrogen rather than nitrogen.
“This planet gets about the same amount of solar radiation as Earth. If the atmosphere is removed as a factor, the temperature of K2-18 b is close to that of Earth, which is also an ideal situation for finding life,” said team member and UCR project scientist Shang. -Min Tsai in a statement.
The main result from the 2023 investigation of K2-18 b, conducted by Cambridge University scientists using the James Webb Space Telescope, was the discovery of carbon dioxide and methane. These molecules were detected without traces of ammonia, suggesting that this world must indeed be a living world with a vast ocean under a hydrogen-rich atmosphere. But there was also a hint of something else, something very exciting.
“What was remarkable, in terms of the search for life, is that last year these researchers reported the preliminary detection of dimethyl sulfide, or DMS, in the atmosphere of this planet, which is produced by oceanic phytoplankton on Earth.” Tsai said. This means that if DMS is accumulating to detectable levels, there must be something on K2-18 b, perhaps a life form, producing it at 20 times the rate on Earth.
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Since the DMS discovery was inconclusive, the leader of the investigation team, Cambridge University scientist Niku Madhusudan, urged caution regarding the DMS discovery. He said future JWST observations will be necessary to confirm its presence in K2-18 b's atmosphere, but not everyone got the memo.
However, this inconclusive nature of the DMS discovery also prompted the UCR team to pursue the discovery.
“The DMS signal from the James Webb Space Telescope was not very strong and only appeared in certain ways when analyzing the data,” Cai said. “We wanted to know if we could confirm what looked like a hint about DMS.”
What this second team found using computer models that account for hydrogen-based atmospheres and in the physics and chemistry of DMS is that the original data are unlikely to indicate the discovery of DMS. “The signal overlaps strongly with methane, and we believe that picking out DMS from methane is beyond the capacity of this tool,” Cai said.
This means that the James Webb Space Telescope will need to look at the world using instruments other than the NIRSS (Near Infrared Imager and Near Infrared Spectrometer) and NIRSpec (Near Infrared Spectrometer) used to conduct the initial investigation that detected hints of the DMS. Fortunately, Madhusudan's team continues to monitor K2–18 b using JWST's other core instrument, MIRI (the Mid-Range Infrared Instrument), as researchers gather more information about environmental conditions on the exoplanet.
“The best biosignatures on an exoplanet may differ significantly from those we find more abundant on Earth today,” said Eddie Schwieterman, team leader and astrobiologist at USC. “On a planet with a hydrogen-rich atmosphere, we may be more likely to find life-made DMS rather than oxygen made by plants and bacteria as is the case on Earth.”
Does this minor disappointment represent a setback for scientists searching the universe for signs of life? It is not a coincidence, nor does it overshadow the importance of preliminary investigation as a step forward in our understanding of the Hessian worlds, which is one of the most promising goals of this research.
“Why do we keep exploring the universe for signs of life?” Cai asked rhetorically. “Imagine you're camping in Joshua Tree at night, and you hear something. Your instinct is to shine the light to see what's there. That's what we do too, in a way.”
The new study discussing these findings was published on May 2 Astrophysical Journal Letters.
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