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Study Reveals Hycean Planets May Be Mostly Desert

9/22/2025

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Summary

Story summary

A study challenges the view that Hycean (sub-Neptune) planets are water-rich, suggesting desert-like worlds.
ETH Zürich researchers find water makes up under 1.5% of a planet’s mass.
Hydrogen and oxygen bind with metals, sequestering water; water-rich atmospheres form on planets formed near stars from molten rock.
Earth may not be unique in having water; K2-18b remains a key target.

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Story summary

A study challenges the view that Hycean (sub-Neptune) planets are water-rich, suggesting desert-like worlds.
ETH Zürich researchers find water makes up under 1.5% of a planet’s mass.
Hydrogen and oxygen bind with metals, sequestering water; water-rich atmospheres form on planets formed near stars from molten rock.
Earth may not be unique in having water; K2-18b remains a key target.