Illustration of the habitable zones around star types. The habitable zone, also known as the Goldilocks zone, is the area around a star where liquid water can exist on the surface of orbiting planets. The illustration shows the relative sizes of habitable zones (left column) for yellow G stars like the Sun (bottom row), along with the zones for orange K dwarf stars (middle row) and red M dwarf stars (top row). The other columns, from left to right, show the relative x-ray radiation for each type of star, their relative abundance and longevity.