How far our planet orbits from the sun, along with other factors such as atmospheric composition, a carbon cycle and the existence of water, has told astronomers much about the conditions that are required for life to not only originate, but to survive on rocky worlds. This distance from a star is referred to, quite simply, as the 'Habitable Zone' or sometimes the 'Goldilocks Zone'' because conditions here are neither too hot or too cold for water to be liquid on the planet’s surface — conditions just right for lifeas we know it to thrive. [ Gallery: The Strangest Alien Planets ]
Copernican theory tells us that our world is a typical rocky planet in a typical planetary system. This concept has spurred some astronomers to start thinking bigger, way beyond the simplicity of any one planetary system and instead towards much grander scales.
Astronomers are exploring whether there is a Galactic Habitable Zone (GHZ) in our Galaxy — a region of the Milky Way that is conducive to forming planetary systems with habitable worlds. The Galactic Habitable Zone implies that if there are conditions just right for a planet around a star, then the same must go for a galaxy.
