Cosmology

The conditions to make life on a planet must meet the conditions necessary to create life on a planet.  The planet must be Earth's size and distance from a similarly sized sun.  It has to have the same physical characteristics of atmosphere, land, water, etc.  Possibly it might require there to be an entire solar system of which only one planet can support biological life as we know and understand it to be.  The best place to be looking for beings such as ourselves is in a similar solar system design.