K2-18b, discovered in 2015 by Kepler’s K2 mission, is a sub-Neptune ~2.6 times Earth’s size orbiting a red dwarf every 33 days. In the habitable zone, JWST confirmed water vapor in 2019—hinting at oceans under a thick atmosphere, though too hot for life as we know it.
Likely a “hycean” world (hydrogen envelope over water), it’s a prime for biosignature hunts.
This planet showed us exoplanet atmospheres are detectable, opening the door to “life signs” searches.