The Galactic Habitable Zone (GHZ) is an area within a galaxy that astronomers believe life can exist. In the Milky Way Galaxy, it’s a ring-shaped region in the galactic plane about 25,000 light-years out from the galactic center. It includes about one-tenth of the stars in our galaxy, including our solar system. What was unusual was that Earth is younger and lies farther from the galactic center than the average life-bearing planet, according to the calculations for the GHZ.

Charles Lineweaver of the University of New South Wales and his colleagues at Swinburne University modeled the Milky Ways’ chemical and dynamical evolution. They chose four prerequisites for complex life: the right chemistry to form terrestrial planets, lots of stars with moderate amounts of heavy elements, an interstellar environment that has remained calm and stable for several billion years, and a low supernova rate.

The team found the GHZ formed as a narrow ring about 8 billion years ago. Over time, the GHZ broadened as heavy elements formed in distant regions of the Milky Way Galaxy. For the first time, man has figured out the most likely area in our galaxy where non-terrestrial life can exist.

The Milky Way’s “ring of life” is similar to the Green Zone in a solar system. The Green Zone is a band in the orbital plane around a star where life could exist. The Green Zone is based on the temperature in the band where water can be in a liquid state. Any planets located in orbit in that band could harbor life. Our solar system has three planets in the Green Zone: Venus, Earth, and Mars. Only Earth has life and water in a liquid state. Venus’ Greenhouse Effect makes it too hot for water to remain liquid so water occurs as vapor in a gaseous state. Mars is too cold for liquid water so the water is frozen as ice in a solid state.