Telescópio Espacial James Webb recorded new atmospheric data from the exoplanet K2-18 b, a celestial body located 124 light-years away from Terra. The information collected indicates the presence of spectral signatures that correspond to dimethylsulfide, a molecule that arouses great interest in the scientific community. The planet orbits the habitable zone of its host star, a region where temperatures allow liquid water to exist. The detection occurred using high-precision instruments that analyze the light filtered by the planet’s atmosphere during its orbital transit.
A team of Universidade researchers from Cambridge led the analysis of data captured in April 2025. Na Terra, dimethylsulfide arises almost exclusively from biological processes linked to phytoplankton in the oceans. The finding reinforces preliminary measurements carried out in 2023, which already showed faint traces of the same chemical compound. The scientists used the telescope’s MIRI instrument, operating at specific infrared wavelengths, to isolate the molecule’s signal amid space noise.
Estrutura physics suggests the existence of a vast global ocean
The Kepler space telescope made the original discovery of K2-18 b in 2015. Measurements indicate that the world has a radius 2.6 times that of Terra and a mass 8.6 times that of our planet. Essa size-to-weight ratio suggests a relatively low average density. Astrophysical models indicate that this physical characteristic results from a composition rich in volatile materials, with a high probability of housing a massive amount of water. The celestial body is part of the category of sub-Neptunes, a type of planet that is extremely common in Via Láctea, but which has no equivalent within Sistema Solar.
Previous Observações conducted by James Webb itself confirmed the abundance of methane and carbon dioxide in the planet’s gaseous layer. Spectral analysis also revealed a notable shortage of ammonia. On purely gaseous planets, ammonia often appears in large quantities. The absence of this specific gas provides a strong indication that the planet has a surface covered in liquid water, hidden beneath a thick hydrogen-dominated atmosphere.
Essa structural configuration defines what astronomers classify as a Hycean world. The theory proposes that a deep, global ocean surrounds the planet’s entire crust, while the upper layer of hydrogen acts as a thermal blanket. The red dwarf star that K2-18 b orbits emits a level of radiation that reaches the planet in proportions similar to the energy that Terra receives from Sol. Climate models applied to this scenario show that water can remain in a stable liquid state.
Principais markers identified in the exoplanet’s orbit
The characterization of distant celestial bodies requires the measurement of multiple parameters simultaneously. The researchers consolidated a detailed technical profile to understand the dynamics of K2-18 b:
- The diameter of the celestial body exceeds the terrestrial size by 2.6 times
- The total mass reaches the equivalent of 8.6 times the weight of the Terra
- The orbital trajectory occurs entirely within the star’s habitable zone
- The atmospheric composition has high levels of methane and carbon dioxide
- Ammonia detection remains at levels well below the gas standard
The set of these chemical and physical characteristics separates K2-18 b from the majority of sub-Neptunes already cataloged by terrestrial and space observatories. The exact combination of gases serves as a natural laboratory for testing theories about planetary formation.
Divergência among experts on the origin of the chemical signal
Dimethylsulfide represents a strong biomarker in the terrestrial context, as no known geological process produces the substance on a large scale. Concentrations estimated from telescope data at K2-18 b exceed quantities found in Terra’s oceans by several orders of magnitude. The Universidade group of Cambridge treated the signal as evidence compatible with biological activity, but avoided classifying the discovery as definitive proof of extraterrestrial life.
Interpretation of the data generated rapid responses from other research institutions. Cientistas of Universidade of Chicago performed an independent reassessment of the same raw information captured by James Webb. The group concluded that the signal identified as dimethylsulfide could be the result of instrumental noise or small variations in the calibration of thermal sensors. Análises joints involving multiple telescope instruments corroborated the statistical fragility of the detection.
The original signal reached a confidence level of three sigma, which represents a 0.3% chance of being a false alarm generated by random fluctuations. Astronomy requires a minimum five-sigma standard to confirm high-impact discoveries, which reduces the margin of error to less than one in a million. Previous Episódios in space exploration, such as the announcement of the detection of phosphine in the atmosphere of Vênus, demonstrate that preliminary three-sigma signals often disappear after data refinement.
Limitações techniques and planning new observations
Spectroscopic data processing involves removing interference caused by the light from the host star and by the equipment itself. Estudos, who crossed information from the NIRISS, NIRSpec and MIRI instruments, demonstrated that the light spectrum of K2-18 b can be explained without the presence of dimethylsulfide. Moléculas alternatives that contain methyl groups in their structure, such as ethane, produce very similar light absorption patterns and can confuse identification algorithms.
Reducing the raw data showed extreme sensitivity to any change in the processing codes. Computational models that included biological gas did not always provide a better fit than simpler simulations based on common molecules. The amount of useful information extracted in the operating range of the MIRI instrument turned out to be lower than the volume of data obtained at shorter wavelengths.
The James Webb telescope ushered in the ability to analyze temperate exoplanet atmospheres with a level of detail impossible for previous generations of observatories. The case of K2-18 b serves as a practical test of the limits of these new observational technologies. Space agencies have already programmed new time windows for the telescope to observe future transits of the planet. The accumulation of new measurements will serve to confirm the existence of the gas or definitively discard the biological hypothesis.