This exoplanet, which lies just 22 light-years from Earth, is at least 4.5 times as massive as Earth, according to NASA's Jet Propulsion Laboratory(opens in new tab). Gliese 667Cc completes one orbit around its host star in a mere 28 days, but that star is a red dwarf considerably cooler than the sun, so the exoplanet is thought to lie in the habitable zone.