What Astrobiologists Really Thought About the 2025 Alien-Life Claims

High-profile reports from 2025 offered two tantalizing possible biosignatures: possible dimethyl sulfide (DMS) or dimethyl disulfide (DMDS) in the atmosphere of exoplanet K2-18b, and unusual mineral “leopard spots” in a Martian rock associated with Cheyava Falls. A rapid survey of astrobiologists found a clear verdict: interest, caution, and no consensus that life had probably been discovered. 12

The headline result: experts were unconvinced

The K2-18b survey received 496 responses. Just 6.6% of respondents agreed or strongly agreed that scientists had probably found extraterrestrial life there; 65.3% disagreed or strongly disagreed, while 28.0% were neutral. 14

The Mars result drew a warmer response, but still fell far short of a discovery-level consensus. 15.1% agreed or strongly agreed that extraterrestrial life had probably been found in the Cheyava Falls case, 44.6% disagreed or strongly disagreed, and 40.3% were neutral. 4

Response	K2-18b	Cheyava Falls, Mars
Strongly agree	0.4%	2.1%
Agree	6.3%	13.0%
Neutral	28.0%	40.3%
Disagree	30.2%	33.5%
Strongly disagree	35.1%	11.1%

The contrast is meaningful. Strong disagreement was much lower for Mars—11.1%, compared with 35.1% for K2-18b—suggesting that researchers saw the Martian evidence as the more compelling of the two. It was not, however, an endorsement that life had been found. 4

Why the K2-18b signal remains unsettled

The K2-18b claim arose from James Webb Space Telescope observations interpreted as possible signatures of DMS and/or DMDS. On Earth, these gases are associated with biological activity, including marine microorganisms, which makes them potential biosignatures rather than direct evidence of alien organisms. 22

That distinction matters because a spectrum is not a sample of an atmosphere. Researchers must determine whether a feature truly identifies a particular molecule, whether the observation is robust across analyses, and whether non-biological chemistry could account for it. Independent reporting and subsequent analyses stressed the need for more data. A later joint analysis of K2-18b’s broad transmission spectrum reported insufficient statistically significant evidence for DMS or DMDS. 2234

So the cautious reading is not that K2-18b is uninteresting. It is that the proposed molecules and their origin have not been securely established.

Why the Mars “leopard spots” are promising but not proof

The Mars case concerns the Sapphire Canyon sample from the Bright Angel formation in Jezero Crater. Its “leopard spots” include minerals such as vivianite and greigite, and the observed chemistry may be consistent with microbial processes. 23

But consistency with life is not the same as confirmation of life. The reported features can also have non-biological geological or chemical explanations. Determining which explanation is correct requires ruling out those alternatives—not merely showing that a biological pathway is possible. 23

That is why the higher level of support for the Mars claim should be understood as greater openness to an unresolved possibility, not evidence that the scientific community has declared ancient Martian life discovered.

A biosignature is a lead, not a conclusion

A biosignature is an observation that could be produced by life and is worth investigating. It becomes persuasive evidence for life only when the observation is reliable and credible non-biological explanations have been tested and excluded.

The two surveys capture this scientific standard in action. Astrobiologists were evaluating particular, incomplete chains of evidence: a difficult-to-interpret remote atmospheric signal on a world more than 100 light-years away, and unusual mineral patterns in a Mars rock that may have multiple origins. Their skepticism was directed at those claims, not at the overall prospect of life beyond Earth.

That broader distinction is especially clear in separate polling: 86.6% of 521 surveyed astrobiologists agreed or strongly agreed that basic extraterrestrial life likely exists somewhere in the universe. 2

The responsible conclusion is therefore both exciting and restrained: K2-18b and Cheyava Falls are important targets for follow-up, but neither result has yet crossed the line from a potential biosignature to proof of extraterrestrial life.