Habitable zones, illustration. The habitable zone surrounding a star, or the region where temperatures would permit liquid water to exist, depends on the type of star. At the top, a planet orbiting a dim red dwarf star has to huddle close (green dot) to be warm enough for liquid water. At the centre, planets orbiting a very hot star, such as a blue giant, would have to be very far away from it before liquid water could exist. At the bottom, planets orbiting too close to a star like our own Sun would be too hot (red dot) while planets orbiting too far away would be too cold (blue dot). Planets orbiting between these two extremes (green dot) would be just right.