A Planetray System or Solar System is a collection of planets and stars. There can be billions of systems in a Galaxy, such as our Milky Way. Although it was known that many contained more than one star, up until the end of the twentieth century, there was no proof that other stars had orbiting planets. Only in recent years have astronomers been able to provide evidence that many, if not most Solar Systems have multiple planets, Asteroids, and comets. Our Solar System is made of 8 planets, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

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 our 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.

Star Systems with Planets

References and External links

Includes material from Liberapedia

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