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Yahoo
09-05-2025
- Science
- Yahoo
Why Astronomers Doubt Claims That Planet K2-18 b Finding Means Alien Life
A University of Cambridge-led team of astronomers made worldwide headlines last night with claims that they had found the 'strongest hints yet of biological activity outside the Solar System'. The discovery involves a distant planet known as K2-18 b, which the team says has one or more molecules in its atmosphere that might have been generated by living things. The announcement has been met with floods of scepticism from other researchers who study such 'biosignatures' in exoplanet atmospheres. 'It is not strong evidence,' says Stephen Schmidt, an astronomer at Johns Hopkins University in Baltimore, Maryland. 'It's almost certainly not life,' says Tessa Fisher, an astrobiologist at the University of Arizona in Tucson. [Sign up for Today in Science, a free daily newsletter] Here, Nature explores the high-profile claim — and why many scientists say it's far from proof of alien life. Using the James Webb Space Telescope (JWST), the Cambridge team reported finding hints of the molecule dimethyl sulfide (DMS), a pungent smelling compound that can be produced by bacteria, in the atmosphere of K2-18 b, a planet smaller than Neptune that lies about 38 parsecs from Earth. The scientists detected the molecule by analysing starlight as it filtered through the planet's atmosphere; different chemical compounds leave identifying imprints in the light's spectrum. The data might indicate the presence of the related molecule dimethyl disulfide (DMDS), either in addition to DMS or in its stead. These chemicals are intriguing because on Earth they are produced by living organisms such as marine phytoplankton. In 2023, the researchers reported similar findings. This follow-up work looks at the planet in a different set of wavelengths and is a stronger and cleaner signal that the molecules are present, the team says. Being able to tease out the detailed chemistry of a faraway planet is a technical tour-de-force, the researchers say. 'What we are seeing is a major paradigm shift in the field of exoplanet science,' said team leader Nikku Madhusudhan, an astronomer at Cambridge, in a livestreamed colloquium on 17 April. He did not respond to a request for an interview before press time for this story. Scientists have been looking for life beyond Earth for centuries. If DMS and DMDS do exist in this planet's atmosphere, and if they are formed by biological activity, it would represent a groundbreaking moment in the search for extraterrestrial life. The work also marks a step toward understanding planets like K2-18 b, which are some of the most common of the 5,800-plus planets that have so far been identified throughout the universe. They are referred to as 'mini Neptunes' based on their mass, but beyond that, little is known about their makeup. Some researchers, including Madhusudhan's team, say that some could be exotic water worlds cloaked in hydrogen atmospheres. If so, they may be some of the best places to look for the existence of extraterrestrial life. For starters, there are questions about whether K2-18 b even has water — or a surface where anything could live. Modelling studies of it and similar planets suggest that they are probably barren. 'A lifeless mini-Neptune scenario remains the most parsimonious explanation,' says Joshua Krissansen-Totton, a planetary scientist at the University of Washington in Seattle. Then there's the issue of whether DMS/DMDS is actually present, or whether it is a spurious signal. The measurement reported by the Cambridge team is 'really pushing the limit of what JWST can do,' says Laura Kreidberg, an astronomer at the Max Planck Institute for Astronomy in Heidelberg, Germany. Schmidt and his colleagues recently re-analysed the 2023 claim from the Cambridge team and found no evidence of biosignature molecules in that data. Schmidt says the new observations are 'pretty noisy, and any reported features could still just be statistical fluctuations'. For their part, the Cambridge researchers say there is just a 0.3% probability that the signal could be due to chance. Finally, if the DMS/DMDS signal is indeed real, then there are many additional questions that need to be resolved before it could be attributed to life, other researchers say. For instance, laboratory experiments have shown that DMS can be made through abiotic processes — those not involving life. 'We know very little about the chemistry of these atmospheres,' says Eleanor Browne, a chemist at the University of Colorado Boulder who led that recent study. Others have reported that DMS is present on a comet explored by the European Space Agency, which definitely does not have life on it. 'The planetary context is what matters,' says Edward Schweiterman, an astrobiologist at the University of California Riverside. If the molecules really are in the planet's atmosphere, he says, 'we have to brainstorm novel ways of producing a lot of it through abiotic means and evaluate those possibilities before accepting it as evidence for life.' Madhusudhan and his colleagues hope to get more observing time with JWST to help nail down the statistical significance of their claim. Beyond that, says Schweiterman, 'what you'd like to see is validation from multiple independent groups.' Regardless of how the claim plays out, it highlights the importance of studying planets like K2-18 b, Kreidberg says: 'This is a very, very rich playground for us to understand how planetary atmospheres work.' This article is reproduced with permission and was first published on April 17, 2025.
Yahoo
26-04-2025
- Science
- Yahoo
Did the James Webb telescope really discover aliens? Here's the truth about K2-18b.
When you buy through links on our articles, Future and its syndication partners may earn a commission. The trendiest planet in the universe right now is K2-18b, a potentially habitable world swirling around a small, red star in the constellation Leo. Located 124 light-years from Earth, the mysterious planet will never host human visitors — but a recent glimpse with the James Webb Space Telescope (JWST) hints that alien life may already thrive there in a vast, warm ocean. In a University of Cambridge-led study published April 17, scientists using JWST reported the detection of possible signs of life in the alien planet's atmosphere, offering what a Cambridge statement called the "most promising" evidence yet of life beyond Earth. However, in the week since the study's publication, a growing number of scientists are already pushing back on this big claim. "The statistical significance of the detection is marginal," Eddie Schwieterman, an assistant professor of astrobiology at the University of California, Riverside who was not involved in the research, told Live Science in an email. "There are some reasons to be skeptical." "It's almost certainly not life," Tessa Fisher, an astrobiologist at the University of Arizona who was not involved in the research, told So what did JWST actually find on K2-18b, and how close are we to solving the ultimate mystery of space? Here's everything you need to know. Unlike optical telescopes such as Hubble, JWST cannot image the surfaces of distant planets directly; instead, its infrared instruments hunt for chemical signs of life — or biosignatures — in planetary atmospheres by mapping how starlight is absorbed or reemitted by molecules in those atmospheres. The resulting graphs of light, called spectra, can reveal the composition of that planet's atmosphere, providing clues about its surface conditions. Related: 32 alien planets that really exist In the new Cambridge-led study, scientists using JWST's Mid-Infrared Instrument (MIRI) peered into K2-18b's atmosphere to detect traces of two sulfur-based molecules called dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) — compounds that are known to be produced only by microscopic life-forms like phytoplankton on Earth. If DMS can be produced by some natural mechanism, scientists currently don't know about it, and will have to run extensive tests to uncover it. The findings add to earlier observations made by the same team using two different JWST instruments in 2023, which also reported possible traces of DMS in the planet's atmosphere. While the Cambridge team admitted in the statement that they are "deeply sceptical" of their own results, the same release also trumpeted these detections as the "most promising" evidence yet of life beyond Earth, painting a picture of an oceanic planet that could be "teeming with life." (Other studies have argued that K2-18b's ocean may, in fact, be made of magma.) Nikku Madhusudhan, lead author of both Cambridge studies, stressed that no actual life has been detected on K2-18b yet. "That's not what we're claiming," Madhusudhan, a professor of astrophysics at Cambridge, told Live Science. "But in the best-case scenario, it's the potential for life." The team's DMS detection reached the three-sigma level of statistical significance, meaning there is a 0.3% probability that the signals occurred by chance. However, this still falls far short of the required five-sigma level that denotes a statistically significant scientific discovery. Responding to criticism that the team may have overstated their study's significance, Madhusudhan said it's in the public interest to know how this research is progressing. "This is the taxpayer paying us, and they have a right to enjoy the process," Madhusudhan added. "If we're sending a robot to Mars, we're not waiting until it goes and finds life to celebrate the act of sending it. We announced that we are sending robots to Mars, and we're excited about the possibility. This is the equivalent of that." For now, the public has little more than the Cambridge team's study to go on. The complete set of MIRI data on which the team based their discovery will become publicly available April 27, according to NPR, at which point outside researchers can begin to comb through it and formulate peer-reviewed responses. In the meantime, various researchers have already attempted to re-create the findings using their own data models and have come up short. In January, a team of scientists independently analyzed K2-18b's atmosphere using the same JWST instruments used in the 2023 study. The team found "no statistically significant or reliable evidence" of DMS on K2-18b, the researchers wrote in a paper published to the preprint server arXiv. More recently, on April 22, University of Oxford astrophysicist Jake Taylor reanalyzed the JWST spectra shared in the new Cambridge study, using a simple data model that's routinely utilized in exoplanet studies. Taylor's analysis, also published to arXiv, found no traces of DMS, either. "There is no strong evidence for detected spectral features in K2-18b's MIRI transmission spectrum," Taylor wrote. Looking only at the Cambridge team's study, Schwieterman also saw cause for hesitation in proclaiming that biosignatures exist on K2-18b. "When DMS interacts with ultraviolet light from the star, it splits apart into components that reform into other molecules like ethane (C2H6) and ethylene (C2H4)," Schwieterman said. "The paper does not report the detection of these molecules, which is puzzling because you'd expect these gases to appear together." Everyone, including the Cambridge team, agrees that more observations of K2-18b are necessary to bring clarity to this puzzle. This means researchers will have to request more time with JWST to observe the alien planet as it swoops in front of its star. Luckily, this is a near-monthly occurrence, with K2-18b completing a transit of its star every 33 days. Budgeting more time to watch these transits should be "trivial" for the telescope, Madhusudhan said. RELATED STORIES —What messages have we sent to aliens? —If life can exist in your stomach, it can exist on Mars. Here's what it might look like. —'Perhaps it's only a matter of time': Intelligent life may be much more likely than first thought, new model suggests "One transit is eight hours, roughly," Madhusudhan added. "You only need about 16 to 24 hours of JWST time. To give you a sense of scale, JWST observes thousands of hours every year." If additional observations can increase the statistical significance of the team's DMS detection, the next step will be to prove that some unknown natural process isn't producing the molecule instead, Schwieterman said. This will take rigorous experimentation and some creative thinking here on Earth. Finally, scientists will need to look at planets that are similar to K2-18b to see if DMS is a common signature around the cosmos.
