By Andy Tomaswick
May 9, 2025
Exceptional claims require extraordinary evidence. This truism, which is known as the “Sagan Standard” after the Science Communication, has been known as “Sagan Standard” since David Hume published it for the first time in the 1740s. But with modern data acquisition, even exceptional evidence is not sufficient – it is the way you interpret it. This is the argument for a new paper paper from Luis Welbank and her colleagues at Arizona State University and various other American institutions. They analyzed the data behind the recent claims of the biosignature detection in the atmosphere of K2-18b and found that other non-biological interpretations could also explain the data.
We previously reported on the detection of Dimethylsulfide (DMS) in the atmosphere of K2-18B, a subneptun exoplanet that circle a star by 124 light years in the constellation Leo. The statement was initially reported in September 2023, whereby recent data from April seemed to support the claim.
However, we have also reported many other explanations for this signal, including explanations for the non-biological creation of the signal and comprehensive discussions about whether the James Webb Space Telescope (JWST), which the data first collected, could even recognize life on other planets. Obviously, claims such as finding life on an exoplanet will collect many skeptics, and this new paper continues in this tradition.
Fraser discusses the latest discoveries on the atmosphere of K2-18B.
However, it is a more statistical approach to its criticism. Rightly rightly claims that it is difficult to recognize individual chemicals in the atmosphere. With the limited data that can provide instruments such as JWST, potential models of the atmosphere have to be compared and recognized with the data that it best represents.
Unfortunately, this requires a lot of statistical assumptions. In order to simplify the process, astronomers generally eliminate entire classes of models to adapt to the “Occam's razor” – the philosophical principle that the simplest explanation is the most likely. For this purpose, use Bayesian model comparison technology, which compares the relative adjustment of two separate models with the data and which is selected better than the more likely scenario.
This practice leads to two problems. First, when all models are poor representations of reality, the one who extends the Bayesian analysis is simply the “least inadequate”. This does not create much trust in the accuracy of the model. On the other hand, this does not necessarily mean that the others are inaccurate if several models fit well with the data, even if you fit better.
Fraser and Pamela discuss one of the most interesting exoplanets that we have found so far – and what it means for the search for life.
In order to prove their point of view, the authors have analyzed the data record that was used in the original biosignature detection paper by several other models that were rejected as part of this paper. They found good adjustments for models that were able to fully explain abiological processes. A certain model that included the hydrocarbon propyne (C3H4) fits better into the data than the model, the DMS and its cousin Dimethyldisulfide (DMD), which was described in April in the work.
The ongoing scientific debate about the interpretation of the data is justified. After all, one of the greatest discoveries in human history would mark one of the greatest discoveries in the history of mankind that it is to be said to have found signs of life for an alien planet. One of the best things about the scientific method is how they treat with disagreements like this. Further data is required to pronounce the concerns of the latest preliminary print and the other articles we have reported. And if scientists collect this data, we will approach the understanding of the truth of the composition of the atmosphere of K2-18 B, even if we need another generation advance – and maybe whether we are not alone in the universe.
Learn more:
L Welbanks et al. – The challenges of recognizing gases in exoplanet atmospheres
Ut – why webb may never be able to find evidence of life in another world
UT – another explanation for K2-18b? A gas-rich mini-new without habitable surface
Ut – is there a life on an alien planet? Fresh knowledge revives the debate
