James Webb Telescope detects possible gas linked to life on oceanic exoplanet 124 light years away

Telescópio Espacial James Webb captured data from the atmosphere of the exoplanet K2-18 b. The planet orbits in the habitable zone of its star, 124 light-years from Terra. A team led by Universidade and Cambridge researchers identified spectral signals compatible with dimethyl sulfide or dimethyl disulfide. Esses compounds, in Terra, arise mainly from marine biological processes.

The observation used the MIRI instrument, which operates at different wavelengths than those used in previous analyses. The signal reached a three sigma level. Isso equates to about a 0.3% chance of being pure noise. The detection occurred in April 2025 and reinforced preliminary data from 2023 that already showed weak traces of the same compound.

K2-18 b was discovered in 2015 by the Kepler telescope. The world is about 2.6 times the radius of Terra and 8.6 times its mass. Modelos indicate density low enough to suggest large amounts of water. The planet belongs to the class of sub-Neptunes, common in the galaxy but absent in Sistema Solar.

Planeta meets the conditions for a possible global ocean

Previous Observações of James Webb, in 2023, confirmed methane and carbon dioxide in the atmosphere of K2-18 b. The absence of ammonia at levels expected for a pure gaseous planet reinforced the idea of ​​an environment with liquid water beneath a layer rich in hydrogen.

Essa combination defines the concept of the Hycean world. Nele, a deep ocean would cover the surface while the upper atmosphere contains hydrogen. The planet receives energy from the star similar to what Terra receives from Sol. Modelos climate conditions indicate that water could exist in a liquid state on a large scale.

• The radius measures 2.6 times that of the Terra
• The mass is equivalent to 8.6 times that of Earth
• The orbit is within the habitable zone
• The atmosphere shows methane and carbon dioxide
• Há low presence of ammonia detected

Esses features differentiate K2-18 b from other sub-Neptunes studied so far.

Dimethylsulfide Detecção divides experts

Dimethylsulfide, or DMS, appears in Terra bound to oceanic phytoplankton. Concentrações estimated at K2-18 b would surpass the terrestrial ones by orders of magnitude. The Cambridge team considered the signal compatible with biological activity, although they avoided definitively affirming life.

Semanas After publication, researchers at Universidade and Chicago re-evaluated the same data. Eles concluded that the signal could result from instrumental noise or calibration variations. Later independent Análises, including a multi-instrument ensemble from James Webb, reinforced the lack of robust statistical evidence for DMS or DMDS.

The three sigma level is below the five sigma standard required for high-impact discoveries in astronomy. Previous Casos, such as phosphine in Vênus, have shown how preliminary signals may not hold up.

Reanálises highlights data limitations

Estudos who combined observations from NIRISS, NIRSpec and MIRI found that the spectrum can be explained without DMS. Outros compounds with methyl groups, such as ethane, produce similar absorption patterns.

Data reduction showed sensitivity to small changes in processing pipelines. Modelos that included DMS did not always outperform simpler versions with fewer molecules. The information content in the MIRI spectrum turned out to be low compared to shorter wavelength bands.

Astrônomos emphasize that James Webb allows us to study the atmospheres of exoplanets in the habitable zone in unprecedented detail. K2-18 b serves as a test for these techniques. Novas observations are scheduled to raise or refute confidence in the signal.

Avanço in characterizing sub-Neptune exoplanets

K2-18 b represents one of the first worlds in the habitable zone with an atmosphere analyzed in multiple spectral bands. Observations confirm methane as the dominant component in some models. Elas also limit the presence of certain gases expected in ocean-free atmospheres.

The debate surrounding DMS illustrates the scientific process. Reanálises independent testing initial results. The community awaits more transits of the planet to accumulate data and reduce uncertainties.

The study of the exoplanet continues. Equipes plans additional observations with James Webb in the coming cycles. The objective is to better map the atmospheric composition and clarify whether non-biological mechanisms explain the detected traces.