The Solar comprises the Sun and the objects that orbit it, whether they orbit it directly or by orbiting other objects that orbit it directly. Of those objects that orbit the Sun directly, the Largest Eight are Planets that form the Planetary System around it, while the remainder are significantly smaller objects, such as Dwarf Planets and small Solar System Bodies (SSSBs) such as Comets and Asteroids.

 

The Solar System formed 4.6 billion Years Ago from the Gravitational Collapse of a giant Molecular Cloud. The vast majority of the System's Mass is in the Sun, with most of the remainder Mass contained in Jupiter. The four smaller Planets, Mercury, Venus, Earth and Mars, aslo called the Terestrial Planets, are primarily composed of Rock and Metal.

 

The four outer Planets, called Gas Giants, are substantially more massive than the Terrestrials. The two largest, Jupiter and Saturn, are composed mainly of Hydrogen and Helium; two the outer most Planets, Uranus and Neptune, are composed largely of substances with relative high melting points 

(compared with Hydrogen and Helium), called Ices, such as Water, Ammonia and Methane, and are often referred to separately as "Ice Giants". All the Planets have almost circular orbits that lie within a nearly flat disc called the Ecliptic Plane.

 

The Solar System also contains regions populated by Smaller Objects. The Asteroid Belt, which lies between Mars and Jupiter, mostly contains objects composed, like the Terrestrial Planets, of Rock and Metal. Beyond Neptune's orbit lies the Kuiper Belt and Scattered Disc, linked populations of Trans-Neptunian Objects composed mostly of Ices. Within these populations are several dozen to more the Ten Thousand objects that may be large enough to have been rounded by their own Gravity. Such objects are referred to as Dwarf Planets. Identified Dwarf Planets include the Asteroid Ceres and the Trans-Neptunian objects Pluto and Eris. In addition to these two regions, various other small-body populations, including Comets, Centaurs and Interplanetary Dust, freely travel between regions. Six of the Planets, at least three of the Dwarf Planets, and many of the smaller bodies are orbited by Natural Satellite, usually termed "Moons" after Earth's Moon.

 

Each of the outer Planets are encircled by Planetary Rings of Dust and other smaller objects. The Solar Wind, a flow of Plasma from the Sun, creates a bubble in the Interstellar Medium known as the Heliosphere, which extends out to the edge of the Scattered Disc. The Oort Cloud, which is believed to be the source for Long-Period Comets, may also exist at a distance roughly a thousand times futher than the Heliosphere. The Heliopause is the point at which pressure form the Solar Winds is equal to the opposing pressure of Intersellar Wind. The Solar System is located in the Orion Arm, 26,000 Light Years from the centre of the Milky Way.