Rocky? Habitable? Sizing up a Galaxy of Planets.

The planets so far discovered across the Milky Way are a motley, teeming multitude: hot Jupiters, gas giants, small, rocky worlds and mysterious planets larger than Earth and smaller than Neptune. As we prepare to add many thousands more to the thousands found already, the search goes on for evidence of life – and for a world something like our own. And as our space telescopes and other instruments grow ever more sensitive, we're beginning to zero in.