Astronomers at NASA’s Ames Research Centre have refuted the hypothesis that exoplanet K2-18b is a gykean – a planet with a hydrogen-rich atmosphere and almost entirely covered by an ocean. According to the study, published in a paper on the arXiv preprint server, it belongs to minineptunes that have no surface.
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K2-18b is located in the habitable zone of the red dwarf at a distance of about 134 light years from Earth. Its radius reaches 2.6 Earth radii and its mass is about 8.6 Earth masses. Because of the planet’s close proximity to its star, its orbital period is only 33 days. But because the star is a dim red dwarf, K2-18b receives about the same amount of energy from its star as Earth does from the Sun.
The planet’s density is between that of Earth and Neptune, meaning it is not composed entirely of rocky rock or gas. It was hypothesised that K2-18b was an oceanic world, which had to be confirmed by studying the composition of the atmosphere.
