We know of over 3,000 planets outside the Solar System, and billions more are waiting to be discovered and characterized.  The eight planets within the Solar System don't take those numbers lying down, though. Thanks to their proximity, these worlds are exceptionally well-studied, at least by exoplanet standards, and can tell us a lot about how we might expect exoplanets to behave.

Tyler D. Robinson, Ph.D. 
Sagan Fellow
University of California, Santa Cruz