Astronomers have confirmed the presence of water on the potential Hykean K2-18 b

Sub-neptune K2—18 b is one of the most promising exoplanets for searching for water outside the Solar System. New data indicate that the planet has either a powerful water shell or an ocean under a hydrogen-helium atmosphere. This is stated in a study published by an international group of astronomers on the website arXiv.org , which Izvestia reviewed on August 2.

The study presents four new observations of the planet's transits through the NIRSpec spectrograph. Based on them, it was possible to accurately determine the content of methane and carbon dioxide in the atmosphere. These data clearly confirm the presence of water in the structure of the planet: either as a saturated water shell with more than 10% of the volume, or as an ocean under a "thin atmosphere".

At the same time, water vapor, ammonia and carbon monoxide could not be detected in the atmosphere. Scientists explain the absence of water vapor by the so—called cold trap, when moisture condenses and settles into the lower layers before reaching the top of the atmosphere. This, according to the researchers, confirms the model of a thin atmosphere over a liquid ocean.

The authors also conducted photochemical modeling of the atmosphere and found only weak, statistically insignificant traces of potential biomarkers — dimethyl sulfide, methyl mercaptan and nitrous oxide. However, even their possible presence does not give grounds to assert the biological origin of the atmosphere.

K2-18 b remains a unique object of study. The planet is much larger than Earth and does not resemble it in structure, but nevertheless may have conditions favorable for the existence of water.

"K2-18 b is a cool, water—rich world that stands out as one of the most promising temperate subneptunes for studying the occurrence of liquid water environments on planets unlike Earth, which motivates further study of its atmosphere and interior," the authors summarize.

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