Planetary systems

Planetary systems are objects that are not part of a star orbiting a star. Planetary systems are composed of planets, moons, asteroids, meteoroids, comets, and cosmic dust. The Solar system is one planetary system. Planetary systems are common in the Galaxy and over 300 Exoplanets are known as of early 2009. Some planets may include Galactic civilizations other than ours. We don't know yet. SETI is looking for them.

References and External links

 * Planetary system