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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. In early 2012 over 700 exoplanets were known. [1] and more are continually discovered. Some planets may include Galactic civilizations older than ours. We don't know yet, SETI is looking for them.

Star Systems with Planets

References and External links

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