Our solar system is home to eight planets, but thus far only Earth is thought to harbor life. There are a number of parameters that define a planet and its relationship towards the sun. These parameters affect a planet's potential to support life. Examples of these parameters include the planetary radius and the orbital radius around the sun.

A planet's orbital radius is its average distance from the sun. This is one of the most important parameters in determining the potential for life to exist on a planet, since it plays a major part in determining planetary temperature. The planetary radius is the distance between a planet's center and its surface. Therefore, planetary radius is a measure of a planet's size.