More Planets Than Stars

There are roughly 100 billion stars in the Milky Way. According to a new study, however, there are even more planets-- perhaps 160 billion-- orbiting their stars in an area corresponding to the expanse between Venus and Saturn. Further, most of those worlds are small and rocky, roughly similar to Earth.

Actually, of course, there are even more planets than that because we know planets orbit stars both inside and outside those boundaries. Just in the Solar System, Mercury orbits inside Venus while Neptune and Uranus orbit outside Saturn. It's also possible that most planets do not orbit stars at all. They are rogue planets, ejected from their home systems, flying through the void of space unattached.