It seems that much of the current research in astrophysics and space science is focused on the search for extraterrestrial life. Whether we are sending probes to Mars, searching for extra-solar planets, or looking for water on moons and planets in our solar system, a major goal of these efforts is discovering environments that are suitable for life, or even finding evidence of life itself. The question of whether or not other life exists is not only an important scientific question, but maybe even a philosophical, sociological, psychological, and theological question as well.
Much of the search for extraterrestrial life has centered on whether or not a planet or moon is in an orbit that permits its surface to retain liquid water. The presence of liquid water is certainly one of the most important requirements for complex life. If a planet's location is too close the star it orbits then it will be too hot and water will boil away, and if a planet is too far from the star, all the water will freeze. The habitable zone is the region in which the planet's orbit is just the right distance from the star to harbor liquid water on its surface.
