The Kepler mission discovered more than 1200 solar system
candidates around other stars. Here is a video showing the orbital motions of all of the
systems that show evidence of multiple planets as of February 2011:
The size of each planet is not shown relative to scale to the size
of their orbits, but the colors do code for size, with red being
the largest, yellow medium, and green the smallest.
The orbital speeds are determined by Newton's law of gravity.
The closer a planet orbits around its parent star, the faster it
orbits. Also the more massive the star, the faster a planet will
orbit given everything else being equal.
A related video was also released for small solar
systems, with planetary orbits less than 0.17 Astronomical Units
(AUs) in size. In comparison, the orbit of Mercury from our Sun is