ScienceAugust 22, 2026

hycean

HY-see-un

Definition

A theoretical type of exoplanet characterized by a massive ocean covering its entire surface and an atmosphere rich in hydrogen.

Etymology

The term is a portmanteau derived from 'hydrogen' and 'ocean'. It was coined in 2021 by astronomers to describe this specific class of potential water worlds.

In the news

The researchers were initially hunting for hycean worlds when they unexpectedly discovered the unusually dense mega-Earth GJ 523b instead.

New “Mega-Earth” Is Massive, On a Very Strange Orbit, And Shouldn't Really Exist

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