Life Colors

There are various indicators that could suggest a planet might harbor life.  The location of its orbit is the first; if it's within the host planet's habitable zone, there's a shot.  Free oxygen in the atmosphere is another good indicator.  Methane's presence means the possibility of life must be seriously considered.

A new study points out that the overall color of a planet is another indicator.  A small planet that is basically blue and within the habitable zone, for example, could indicate a water world.  A similar world similarly positioned, but greenish, may mean that world is awash in chlorophyll, suggesting vegetation.  Spectroscopic analysis of the light bouncing off such a planet-- breaking down the light into its constituent parts-- could then give more details about the makeup of an alien atmosphere.