Claim: A planet is in the Solar System.

The Solar SystemCapitalization of the name varies . The International Astronomical Union , the authoritative body regarding astronomical nomenclature , specifies capitalizing the names of all individual astronomical objects , but uses mixed `` Solar System '' and `` solar system '' in their naming guidelines document . The name is commonly rendered in lower case -LRB- `` solar system '' -RRB- , as , for example , in the Oxford English Dictionary and Merriam-Webster 's 11th Collegiate Dictionary . is the gravitationally bound system comprising the Sun and the objects that orbit it , either directly or indirectly.The natural satellites -LRB- moons -RRB- orbiting the Solar System 's planets are an example of the latter . Of those objects that orbit the Sun directly , the largest eight are the planets , Historically , several other bodies were once considered planets , including , from its discovery in 1930 until 2006 , Pluto . See Former planets . with the remainder being significantly smaller objects , such as dwarf planets and small Solar System bodies . Of the objects that orbit the Sun indirectly , the moons , two are larger than the smallest planet , Mercury.The two moons larger than Mercury are Ganymede , which orbits Jupiter , and Titan , which orbits Saturn . Although bigger than Mercury , both moons have less than half the mass of Mercury .   The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud . The vast majority of the system 's mass is in the Sun , with the majority of the remaining mass contained in Jupiter . The four smaller inner planets , Mercury , Venus , Earth and Mars , are terrestrial planets , being primarily composed of rock and metal . The four outer planets are giant planets , being substantially more massive than the terrestrials . The two largest , Jupiter and Saturn , are gas giants , being composed mainly of hydrogen and helium ; the two outermost planets , Uranus and Neptune , are ice giants , being composed mostly of substances with relatively high melting points compared with hydrogen and helium , called volatiles , such as water , ammonia and methane . All planets have almost circular orbits that lie within a nearly flat disc called the ecliptic .   The Solar System also contains smaller objects . The asteroid belt , which lies between the orbits of Mars and Jupiter , mostly contains objects composed , like the terrestrial planets , of rock and metal . Beyond Neptune 's orbit lie the Kuiper belt and scattered disc , which are populations of trans-Neptunian objects composed mostly of ices , and beyond them a newly discovered population of sednoids . Within these populations are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity . Such objects are categorized 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 clouds , freely travel between regions . Six of the planets , at least four of the dwarf planets , and many of the smaller bodies are orbited by natural satellites , See List of natural satellites of the Solar System for the full list of natural satellites of the eight planets and first five dwarf planets usually termed `` moons '' after the Moon . Each of the outer planets is encircled by planetary rings of dust and other small objects .   The solar wind , a stream of charged particles flowing outwards from the Sun , creates a bubble-like region in the interstellar medium known as the heliosphere . The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium ; it extends out to the edge of the scattered disc . The Oort cloud , which is thought to be the source for long-period comets , may also exist at a distance roughly a thousand times further than the heliosphere . The Solar System is located in the Orion Arm , 26,000 light-years from the center of the Milky Way .