World Types

A proposed class of exoplanet — a hot world with a hydrogen-rich atmosphere over a planet-wide ocean. If they exist, hycean planets would offer a much wider habitable zone than rocky worlds and be easier to study, but the class is hypothetical and its habitability unconfirmed.

A rocky exoplanet orbiting so close to its star that its day side is hot enough to melt rock, covering it in a global magma ocean. Several known super-Earths, such as 55 Cancri e, are thought to be lava worlds, offering a natural laboratory for molten-rock chemistry.

A world with a large body of liquid water — most securely the global oceans hidden beneath the ice of moons like Europa and Enceladus, and possibly some water-rich exoplanets. Ocean worlds are among the most promising places to search for life beyond Earth.