NASA's Kepler spacecraft has discovered 170 planetary systems containing between two and six transiting planets. This animation shows all the multiple-planet systems discovered by Kepler as of 2/2/2011; orbits go through the entire mission (3.5 years). Hot colors to cool colors (red to yellow to green to cyan to blue to gray) are big planets to smaller planets, relative to the other planets in the system. Credit: Daniel Fabrycky