25-05-2025
Doubts over hope of alien life on exoplanet K2-18b as case for biosignatures weakens
A growing number of studies have cast doubt on earlier claims about signs of life on K2-18b, a planet 124 light-years away in the Leo constellation, concluding that the available data doesn't support such bold interpretations.
Last month, scientists had announced that they might have identified what appeared to be the most promising signs of alien life discerned so far on the distant planet. However, latest research contends that there was not enough evidence to estimate alien presence.
K2-18b orbits within the habitable zone of its star, making it a compelling target for the search of alien life due to the potential presence of liquid water.
Astronomers working with the James Webb Space Telescope drew global attention in April by reporting possible traces of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in the planet's atmosphere.
On Earth, these compounds are produced exclusively by living organisms such as marine algae, which is why they are considered potential biosignatures—chemical hints that life might exist elsewhere.
Led by Cambridge University's Nikku Madhusudhan, the research team was careful to stress that the potential biosignature was far from conclusive. The signal reached a three-sigma level of statistical significance, meaning there remains a small but meaningful possibility that the result was a fluke.
Two of Madhusudhan's former students, Luis Welbanks of Arizona State University and Matthew Nixon of the University of Maryland, were part of a team that re-examined the data behind the initial announcement.
In a preprint study published online towards the end of last month, they reported that when using alternative statistical models, the signals originally interpreted as potential biosignatures no longer stand out. In one approach, the researchers broadened the pool of possible atmospheric chemicals from 20 to 90, significantly weakening the case for a unique biological explanation.
Embracing the ongoing scientific discussion, Madhusudhan highlighted the importance of keeping an open mind throughout the research process. His team added to the conversation by releasing a new preprint study last week that expanded the list of potential atmospheric chemicals to 650.
Among the top candidates identified as an indicator of alien life was dimethyl sulfide (DMS). Meanwhile, dimethyl disulfide (DMDS), which had featured prominently in their earlier announcement, was no longer considered a leading possibility.
Astronomers observe distant exoplanets like K2-18b by tracking their passage across their host stars, which allows them to analyze how molecules in the planet's atmosphere absorb specific wavelengths of starlight.
Earlier this week, a study led by postdoctoral researcher Rafael Luque at the University of Chicago combined Webb's observations of K2-18b in both near-infrared and mid-infrared wavelengths. The research found no statistically significant evidence for dimethyl sulfide (DMS) or dimethyl disulfide (DMDS).
In addition, an earlier paper by Oxford astrophysicist Jake Taylor, using a basic statistical method, also reported no strong signs of biosignatures.
However, Madhusudhan dismissed Taylor's paper noting the simple exercise used to draw conclusions was far from a robust method to observe physical phenomena. The scientist also highlighted that more data on K2-18b will be collected over the next year, which should help provide a clearer and more definitive picture.
