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A small sign that was revealed in April, seemed as if it could change the universe as we know it.
Astronomers had only discovered a hint, a glimpse of two molecules that swirl in the atmosphere of a distant planet called K2-18B molecules that are only produced on earth by living beings. It was a seductive prospect: the most promising evidence so far from an alien biosignature, or traces of life linked to biological activity.
But only weeks later new findings suggest that the search must continue.
“It was exciting, but it immediately increased different red flags because that claim of a potential biosignature would be historical, but also the meaning or strength of statistical evidence seemed to be too high for the data,” said Dr. Luis Welbanks, a post -doctoral research scholar at the Arizona State University's School of Earth and Space Exploration.
While the molecules identified on K2-18B by the investigation of April-Dimethylsulfide, or DMS and Dimethyldisulfide, or DMD's-grotendeels are associated with microbial organisms on our planet, scientists point out that the connections can also form without the presence of life. Now three teams of astronomers that are not involved in the research, including Welbanks, have assessed the models and data that are used in the original discovery of biosignature and have received very different results that they have submitted for Peer Review.
In the meantime, the main author of the April study, Nikku Madhusudhan, and his colleagues, have conducted additional research that, according to them, strengthens their earlier finding about the planet. And it is likely that additional observations and research from several groups of scientists are on the horizon.
The succession of research documents around K2-18B offers a glimpse of the scientific process that unfolds in real time. It is a window in the complexity and nuances of how researchers are looking for proof of life beyond the earth – and shows why the burden of proof is so high and difficult to reach.
Noisy data
Located on 124 light years of the earth, K2-18B is generally considered a worthy target to sand into signs of life. It is thought that it is a hycean world, a planet that is completely covered with liquid water with a hydrogen -rich atmosphere, according to earlier research led by Madhusudhan, a professor in astrophysics and exoplanetary science at the Astronomy Institute of the Cambridge University. And as such, K2-18B quickly attracted attention as a potentially habitable place outside of our solar system.
Convinced of the promise of K2-18B, Madhusudhan and his Cambridge colleagues used observations of the planet through the largest space telescope in use, the James Webb Space Telescope, to further study the planet. But two scientists at the University of Chicago – Dr. Rafael Luque, a postdoctoral scholar at the Ministry of Astronomy and Astrophysics of the University, and Michael Zhang, a 51 Pegasi B / Burbidge Postdoctoral Fellow – saw some problems with what they found.
After revising Madhusudhan and the April paper of his team, who followed their 2023 investigation, Luque and Zhang noted that the Webb data looked “noisy,” Luque said.
Ruis, caused by imperfections in the telescope and the speed with which different particles of the light reach the telescope, is only one challenge that astronomers are confronted when they study exoplanets remotely. Ruis can distort observations and introduce uncertainties in the data, Zhang said.
Trying to detect specific gases in distant exoplanet -atmospheres introduces even more uncertainty. The most striking features of a gas -like dimethyl sulfide of a binding of hydrogen and carbon molecules – a connection that can stretch and bend and can absorb light on different wavelengths, making it difficult to finally detect a kind of molecule, Zhang said.
“The problem is in fact that every organic molecule has a carbon -hydrogenic bond,” said Zhang. “There are hundreds of millions of those molecules, and so these functions are not unique. If you have perfect data, you can probably distinguish between different molecules. But if you do not have perfect data, many molecules, especially organic molecules, look very similar, especially in the near infrared.”
Luque and Zhang also ran further in the paper and also noticed that the observed temperature of the planet seemed to rise sharply from a range from approximately 250 Kelvin to 300 Kelvin (-9.67 f to 80.33 F or -23.15 C to 26.85 C) in investigation published in 2023 to 422 Celvin in the study of the study of the study of Kelvin.
Such hard temperatures could change the way astronomers think about the potential habitability of the planet, Zhang said, especially since cooler temperatures in the top of the atmosphere continue to exist – the area that can detect webb – and the surface or ocean below would probably have even higher temperatures.
“This is just a conclusion only from the atmosphere, but it would certainly influence how we think about the planet in general,” said Luque.
Part of the problem, he said, that the April analysis did not collect the data collected from all three WebB instruments that the Madhusudhan team has used in recent years. So Luque, Zhang and their colleagues have carried out a study that combines all available data to see if they could achieve the same results, or even find a higher amount of dimethylsulfide. They found “insufficient evidence” of both molecules in the atmosphere of the planet.
Instead, the Luque and Zhang team saw other molecules, such as Ethane, who could fit the same profile. But Ethane means no life.
Disappearing evidence
Welbanks from Arizona State and his colleagues, including Dr. Matt Nixon, a postgraduate researcher from the Department of Astronomy of the University of Maryland College Park, also found what they considered as a fundamental problem with the April Paper on K2-18B.
The care, said Welbanks, was with how Madhusudhan and his team created models to show which molecules can be in the atmosphere of the planet.
“Each (molecule) is tested one by one at the same minimal basic line, which means that each model has an artificial advantage: it is the only permitted explanation,” said Welbanks.
When Welbanks and his team performed their own analysis, they expanded the model of Madhusudhan's study.
“(Madhusudhan and his colleagues) did not allow other chemical species that could possibly produce these small signals or observations,” said Nixon. “So the most important thing we wanted to do was assess whether other chemical species fits sufficiently with the data.”
When the model was expanded, “the evidence for Dimethylsulfide or Dimethyldisulfide” disappears “just,” said Welbanks.
Burden
Madhusudhan believes that the studies that were released in April in April were “very encouraging” and “make a healthy discussion possible about the interpretation of our data about K2-18B.”
He assessed the work of Luque and Zhang and agreed that their findings do not show “strong detection for DMS or DMDs”. When the Madhusudhan team published the newspaper in April, he said that the observations reached the significant level of three Sigma, or a probability of 0.3% that the detections happened to take place.
For a scientific discovery that is very unlikely that it happened to occur, the observations must meet a threshold of five Sigma, or under a probability of 0.00006% that the observations happened to take place. Meeting such a threshold will require a lot of steps, said Welbanks, including repeated detections of the same molecule with the help of multiple telescopes and the exclusion of potential non -biological sources.
Although such evidence can be found in our lives, it is less likely a Eureka moment and more a slow build that requires a consensus in astronomers, physicists, biologists and chemists.
“We have never reached that level of evidence in one of our studies,” wrote Madhusudhan in an e -mail. “We have only found evidence on or under 3-sigma in our two previous studies (Madhusudhan et al. 2023 and 2025). We call this moderately evidence or hints, but not strong detection. I agree with (Luque and Zhang's) that is consistent with our studies and we have discussed the need for stronger proof.”
In response to the research of the Welbanks team, Madhusudhan and his Cambridge colleagues have written another manuscript in which the search on K2-18B is expanded with 650 types of molecules. They have submitted the new analysis for Peer Review.
“This is the largest search for chemical signatures in an exoplanet so far, using all available data for K2-18B and the search for 650 molecules,” said Madhusudhan. “We see that DMS remains a promising candidate -molecule on this planet, although more observations are required for a solid detection as we have noticed in our earlier studies.”
Welbanks and Nixon were delighted that Madhusudhan and his colleagues have tackled the spells, but have the feeling that the new paper will effectively decline the central claims in the original April study, Welbanks said.
“The new paper tacitly admits that the DMS/DMDS detection was not robust, but still trusts the same inadequate statistical framework and a selective reading of his own results,” said Welbanks in an e -mail. “Although the tone is more cautious (sometimes), the methodology continues to obscure the true level of uncertainty. The statistical significance that was claimed in earlier work was the product of random modeling decisions that are not recognized.”
Luque said that the new article from the Cambridge team is a step in the right direction because it is investigating other possible chemical biosa signatures.
“But I think it is inadequate in the scope,” said Luque. “I think it is too limited to a refutation of the (Welbanks) paper.”
However, separately, the astronomers who study K2-18B agree that continuing to investigate the exoplanet contribute to the scientific process.
“I think it's just a good, healthy scientific discourse to talk about what's going on with this planet,” said Welbanks. “Regardless of what a single authors' group says now, we don't have a silver bullet. But that is precisely why this is exciting, because we know that we are the closest that we have ever been (to find a biosignature), and I think we can get it within our lives, but we are not there at the moment.
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