K2-18b is an exoplanet studied for its atmosphere and the possibility that it has temperate conditions.
K2-18b is an exoplanet larger than Earth but smaller than Neptune. It orbits a red dwarf about 120–124 light-years away in the constellation Leo. Discovered in 2015 by the Kepler Space Telescope’s K2 mission, the planet has about 8.6–8.9 times Earth’s mass and 2.4–2.6 times its radius.
K2-18b orbits its star every 33 days or so, at a distance of about 21 million kilometers. It lies in the star’s habitable zone. Observations by the Hubble and James Webb space telescopes detected water vapor in its atmosphere, followed by carbon dioxide and methane. These findings prompted the hypothesis that K2-18b may be a «Hycean» world, potentially with a global ocean. Observations have not confirmed the existence of such an ocean.
In 2025, a research team reported possible spectral signatures of DMS and DMDS, substances that may be associated with biological activity on Earth. The findings remain under examination and are controversial. There is currently no confirmed biosignature or evidence of life on K2-18b, which remains a promising target for studying exoplanets and the possibility of habitability.
Yes. It is an exoplanet confirmed after its discovery in 2015.
Observations have detected water vapor in its atmosphere. The existence of a liquid ocean on the planet’s surface has not been confirmed.
No. In 2025, researchers reported possible signs of substances that may be associated with life, but these have not been confirmed and are not evidence of life.
Yes. It lies in its star’s habitable zone, where the radiation it receives is roughly comparable to what Earth receives. This does not prove that the planet has life or conditions suitable for it.