Our Solar System

Visual Summary

A sampling of closely imaged Solar System bodies, selected for size and detail. The Sun is approximately 10,000 times larger than, and 41 trillion times the volume of, the smallest object shown (Prometheus). See alsoList of Solar System objects by size,List of natural satellites,List of minor planets, andLists of comets. Images here are not an endorsement of natural color in visible light.

Solar System Summary

Sun	Jupiter	Saturn	Uranus	Neptune	Earth	Venus

Formation and Evolution

The Solar System formed from the gravitational collapse of a giant molecular cloud 4.568 billion years ago. This initial cloud was likely several light-years across and probably birthed several stars. A shock wave from a nearby supernova may have triggered the formation of the Solar System by creating regions of over-density within the molecular cloud and causing these regions to collapse.

As the region that would become the Solar System, known as the 

Galactic Context

Location of the Solar System within ourgalaxy

The Solar System is located in the Milky Way galaxy, a barred spiral galaxy with a diameter of about 100,000 light-years containing about 200 billion stars. Our Sun resides in one of the Milky Way's outer spiral arms, known as the Orion Arm or Local Spur. The Sun lies between 25,000 and 28,000 light years from the Galactic Centre, and its speed within the galaxy is about 220 kilometres per second, so that it completes one revolution every 225–250 million years. This revolution is known as the Solar System's 

Farthest Regions

The point at which the Solar System ends and interstellar space begins is not precisely defined, since its outer boundaries are shaped by two separate forces: the solar wind and the Sun's gravity. The outer limit of the solar wind's influence is roughly four times Pluto's distance from the Sun; this heliopause is considered the beginning of the interstellar medium. However, the Sun's Roche sphere, the effective range of its gravitational dominance, is believed to extend up to a thousand times farther.

Heliopause

NASA image of the heliosheath and heliopause

The heliosphere is divided into two separate regions. The solar wind travels at roughly 400 km/s until it collides with the interstellar wind; the flow of plasma in the interstellar

Trans-Neptunian region

The area beyond Neptune, or the "trans-Neptunian region", is still largely unexplored. It appears to consist overwhelmingly of small worlds (the largest having a diameter only a fifth that of the Earth and a mass far smaller than that of the Moon) composed mainly of rock and ice. This region is sometimes known as the "outer Solar System", though others use that term to mean the region beyond the asteroid belt.

Kuiper belt

Plot of all known Kuiper belt objects, set against the four outer planets

The Kuiper belt, the region's first formation, is a great ring of debris similar to the asteroid belt, but composed mainly of ice. It extends between 30 and 50 AU from the Sun. Though it contains at least three dwarf planets, it is composed mainly of small Solar System bodies. However, many of the largest Kuiper belt objects, such as Quaoar, Varuna, and Orcus, may be reclassified as dwarf planets. There are estimated to be over 100,000 Kuiper belt objects with a diameter greater than 50 km, but the total mass of the Kuiper belt is thought to be only a tenth or even a hundredth the mass of the Earth. Many Kuiper belt objects have multiple satellites, and most have orbits that take them outside the plane of the ecliptic.

The Kuiper belt can be roughly divided into the "classical" belt and the resonances. Resonances are orbits linked to that of Neptune (e.g. twice for every three Neptune orbits, or once for every two). The first resonance begins within the orbit of Neptune itself. The classical belt consists of objects having no