Circumstellar Habitable Zones
The Circumstellar Habitable Zone (hereafter CHZ) is defined as the region around a star where water could exist on the surface of an Earth-like planet. Water is believed to have been vital in the formation of life on Earth due to its function as a solvent in biochemistry. Although the region is a spherical shell that surrounds a star, it is often shown as a ring in diagrams looking down onto the plane of a star system. Realize that the CHZ is closely related to the inverse square law – how energy falls off with distance from a star. Thus, the size and location of the CHZ change over time as a star evolves. For the Sun at present the CHZ ranges from 0.97 AU to 1.37 AU.