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[[File:lighterstill.jpg]][[File:Solar-system.jpg|right|frame]]

[[File:lighterstill.jpg]][[File:Solar-system_1.jpg|right|frame]]

The '''Solar System''' consists of the [[Sun]] and those [[celestial]] objects bound to it by [[gravity]], all of which formed from the collapse of a giant [http://en.wikipedia.org/wiki/Molecular_cloud molecular cloud] approximately 4.6 billion years ago. Of the retinue of objects that [[orbit]] the Sun, most of the [[mass]] is contained within eight [[relatively]] [[solitary]] [[planets]] whose orbits are almost [[circular]] and lie within a nearly-flat disc called the [http://en.wikipedia.org/wiki/Plane_of_the_ecliptic ecliptic plane]. The four smaller inner planets, [http://en.wikipedia.org/wiki/Mercury_(planet) Mercury], [http://en.wikipedia.org/wiki/Venus Venus], [http://en.wikipedia.org/wiki/Earth Earth] and [http://en.wikipedia.org/wiki/Mars Mars], also called the [[terrestrial]] planets, are primarily composed of rock and metal. The four outer planets, [http://en.wikipedia.org/wiki/Jupiter Jupiter], [http://en.wikipedia.org/wiki/Saturn Saturn], [http://en.wikipedia.org/wiki/Uranus Uranus] and [http://en.wikipedia.org/wiki/Neptune Neptune], also called the [http://en.wikipedia.org/wiki/Gas_giants gas giants], are composed largely of hydrogen and helium and are far more massive than the terrestrials.

The '''Solar System''' consists of the [[Sun]] and those [[celestial]] objects bound to it by [[gravity]], all of which formed from the collapse of a giant [http://en.wikipedia.org/wiki/Molecular_cloud molecular cloud] approximately 4.6 billion years ago. Of the retinue of objects that [[orbit]] the Sun, most of the [[mass]] is contained within eight [[relatively]] [[solitary]] [[planets]] whose orbits are almost [[circular]] and lie within a nearly-flat disc called the [http://en.wikipedia.org/wiki/Plane_of_the_ecliptic ecliptic plane]. The four smaller inner planets, [http://en.wikipedia.org/wiki/Mercury_(planet) Mercury], [http://en.wikipedia.org/wiki/Venus Venus], [http://en.wikipedia.org/wiki/Earth Earth] and [http://en.wikipedia.org/wiki/Mars Mars], also called the [[terrestrial]] planets, are primarily composed of rock and metal. The four outer planets, [http://en.wikipedia.org/wiki/Jupiter Jupiter], [http://en.wikipedia.org/wiki/Saturn Saturn], [http://en.wikipedia.org/wiki/Uranus Uranus] and [http://en.wikipedia.org/wiki/Neptune Neptune], also called the [http://en.wikipedia.org/wiki/Gas_giants gas giants], are composed largely of hydrogen and helium and are far more massive than the terrestrials.