TOO HOT TOO COLD JUST RIGHT Star Planet The habitable zone,or “Goldilocks zone,” is the orbital distance from a star in which a planet’s atmosphere allows water to exist in liquid form at the planet’s surface. So far, that is the only known habitat supporting life. Hot zone:Temperatures are too high for water to exist as a liquid. Cold zone:Some scientists theorize that on cold planets outside the habitable zone, life might exist where water is kept liquid through tidal heating or radioactive decay.

SOURCE: American Association for the Advancement of Science, Proceedings of the National Academy of Sciences, Astrophysical Journal, Science, MIT Technology Review.