Survey Finds Scientists Far More Cautious on Alien-Life Claims Than Headlines Suggest

When two closely watched 2025 announcements suggested possible signs of extraterrestrial life, a research group at Durham University surveyed hundreds of astrobiologists within days of each to find out what scientists actually thought — and found far more caution than the headlines suggested.

The first announcement came in April 2025, when researchers reported possible traces of two molecules, dimethyl sulfide and dimethyl disulfide, in the atmosphere of the exoplanet K2-18b; on Earth, these compounds are associated with biological activity, and media coverage widely framed the finding as an extraordinary advance in the search for alien life. The second came in September, when NASA said a Martian rock called Cheyava Falls appeared to preserve a potential biosignature — mineral "leopard spot" rings that, on Earth, are often formed by microbial activity.

For K2-18b, only 6.6% of surveyed astrobiologists agreed that scientists had probably found extraterrestrial life, while nearly two-thirds disagreed and 28.0% remained neutral, according to the survey by Durham's C-Scope research group.

For the Mars case, confidence was higher but still cautious: 15.1% agreed, disagreement fell to 44.6% and neutrality rose to 40.3%. The share of astrobiologists who strongly disagreed fell sharply, from 35.1% for K2-18b to just 11.1% for Mars — showing that most of the shift was from strong rejection toward more tentative skepticism, not toward actual endorsement.

One possible reason for the difference, the researchers say, is that the two cases involved different kinds of evidence: the K2-18b claim relied on atmospheric signals detected across interstellar distances, while the Martian case concerned a rock that could be studied directly and in much greater detail.