Survey finds 6.6% of astrobiologists think K2-18 b life probably found

The survey went out within days of the April 2025 K2-18 b announcement and Nasa's September 2025 statement about the Cheyava Falls rock on Mars. It asked hundreds of astrobiologists from across the global research community whether scientists thought extraterrestrial life had probably been found. For K2-18 b, 28.0% of respondents stayed neutral.

For the Mars case, 15.1% agreed, 44.6% disagreed and 40.3% were neutral, the survey found. Strong disagreement fell from 35.1% for K2-18 b to 11.1% for Mars. The authors read that as movement from strong rejection towards tentative positions, not a swing to endorsement. They also noted that press officers and journalists tend to quote a handful of experts, which rarely shows what the wider community thinks.

The K2-18 b claim

The Times of India reported that K2-18 b is 124 light-years from Earth and orbits in its star's habitable zone. The claim dates to April 2025, when Nikku Madhusudhan's Cambridge team reported possible traces of dimethyl sulfide and/or dimethyl disulfide in the planet's atmosphere, the BBC reported. On Earth, the gases are produced by marine phytoplankton and bacteria. The BBC reported that the detection was a three-sigma result, or 99.7% confidence, short of the five-sigma standard for a discovery. The Times of India reported that this leaves a 0.3% chance the result is a statistical fluke. Catherine Heymans of Edinburgh University, who is independent of the research team, told the BBC that even a five-sigma result would leave the origin of the gas open. The Times of India reported that some researchers argue K2-18 b could be a molten-rock world or a mini gas giant instead of an ocean world. Fox 5 Atlanta reported that the estimated concentrations were over 10 parts per million, against below 1 part per billion by volume on Earth. Madhusudhan told the BBC the amount was thousands of times higher than Earth's.

The rebuttal

A team led by Lewis Welbanks at Arizona State University analyzed 90 molecules that could form on K2-18 b, Dongascience reported. It found that 59 could produce the observed signals through sunlight-driven chemistry alone. The team said propyne gas had a high probability of creating the dimethyl sulfide signal in particular. The team was not arguing that propyne exists there.

What comes next

At a news conference, Madhusudhan said: "It is in no one's interest to claim prematurely that we have detected life," Fox 5 Atlanta reported. He said he wanted further theoretical and experimental work to test whether DMS and DMDS can be produced non-biologically at the level currently detected. He told the BBC he could realistically confirm the signal within one to two years.