the cosmic real estate rating system where liquid water is the only listing that matters.
means an estimate of whether a planet orbiting another star could support liquid water on its surface, based on its distance from its star, size, and atmosphere.
from the term crystallized around the concept of the habitable zone, first modeled in the 1950s-70s by astronomers calculating where a planet's temperature would let water stay liquid rather than freeze or boil away; nicknamed the goldilocks zone because the orbit has to be just right.
proxima centauri b — nearest potentially habitable exoplanet, 4.2 light-years away, found 2016
trappist-1e — one of seven earth-sized planets, 2017 discovery, tightly packed system
kepler-452b — 2015 find nicknamed earth's cousin, 60 percent bigger than earth
teegarden b — 2019 discovery, near-earth mass orbiting a tiny red dwarf star