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Solar System
Planets2013
The Sun and planets of the Solar System

(distances not to scale)

Stars

1 (Sun)

Known planets

8 (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune)

Known dwarf planets

Possibly several hundred; five currently recognized by the IAU (Ceres, Pluto, Haumea, Makemake, Eris)

Known natural satellites

470 (173 planetary, 297 minor planetary)

Known minor planets

707,664 (as of 2016-03-07)

Known comets

3,406 (as of 2016-03-07)

Identified rounded satellites

19

Age

4.568 billion years

Location

Local Interstellar Cloud, Local Bubble, Orion–Cygnus Arm, Milky Way

The Solar System consists of the Sun and those celestial objects bound to it by gravity: the eight planets and five dwarf planets, their 173 known natural satellites (usually termed "moons"), and billions of small bodies. The small bodies include asteroids, icy Kuiper belt objects, comets, meteoroids, and interplanetary dust.

The charted regions of the Solar System comprise the Sun, four terrestrial inner planets, the asteroid belt, four gas giant outer planets, and finally the Kuiper belt and the scattered disc. The hypothetical Oort cloud may also exist at a distance roughly a thousand times beyond these regions. The solar wind, a flow of plasma from the Sun, permeates the Solar System, creating a bubble in the interstellar medium known as the heliosphere, which extends out to the middle of the scattered disc.

Formation of the Solar SystemEdit

The Solar System was formed approximately five billion years ago by a nebula cloud. When this cloud began a process of rotating, it began to compact due to a force known as accretion, a force caused by matter compacting together and forming layers that create pressure and create a solid or gaseous-like material depending on the amount of gravity reacting on the object from a nearby gravitational emitting source (in this case, the Sun). After this process, the gas created the Sun, using up 99.86% of all of the Solar System's matter and mass. The rest of the cloud was used to form the inner and outer planets.

There are two main regions in the Solar System: the inner planets and the outer planets. These regions are seperated by a region known as the Asteroid belt. This belt is bordered by Mars and Jupiter.

Inner PlanetsEdit

800px-Terrestrial planet size comparisons
The inner planets of the Solar System, Mercury, Venus, Earth, and Mars, are the four innermost planets of the Solar System. These planets are rocky due to their distance from the Sun and since their portion of the cloud was exposed to more accretion during their formation. The inner planets are also referred to as the terrestrial, or rocky, planets. Only one of these inner planets, Earth, is known to support life, which is the planet we live on. These planets have been known since ancient times.

Outer PlanetsEdit

466px-Gas giants in the solar system
The outer planets of the Solar System, Jupiter, Saturn, Uranus, and Neptune, are the four outermost planets of the Solar Sysrem. These planets are all gaseous and are the largest planets in the Solar System. In fact, Jupiter is the largest planet in the Solar System. These planets also harness the most of amount of moons, with Jupiter having the most at 66 known satellites, and is also home to Ganymede, the largest moon in the Solar System, being larger than the planet of Mercury. The outer planets are referred to as the gas giants. None of these planets have been known since ancient times. In fact, the earliest date these planets were found were by Galileo Galilei, who found the two planets Jupiter and Saturn, not to mention the Great Red Spot and four of Jupiter's moons. William Herschel found Uranus and three astronomers (listed in Neptune article) found Neptune.

Dwarf PlanetsEdit

The dwarf planets of the Solar System, Pluto, Eris, Ceres, Makemake, and Haumea, are the second smallest celestial bodies in the Solar System, just barely surpassing the satellites belonging to the much larger planets. These bodies are so small, they are actually asteroids that were large enough to sustain themselves in a spherical shape. These bodies are even too small to pull in their own satellites, although Pluto, Haumea, and Eris have attracted some asteroids that they have been able to sustan in their gravitational pulls and are classified as satellites. Before more classifications for celestial bodies were established, there were fifteen planets in the Solar System, with the other seven made up of various dwarf planets. Ceres, the innermost of the dwarf planets, is actually inside of the Asteroid belt, while the others, such as Pluto and Eris, belong or even surpass the Kuiper Belt, another region surpassing the planet of Neptune. These objects surpassing Neptune are known as Trans-Neptunian objects. These planets also have not been known since ancient times because of their distance Earth, let alone the Sun. In fact, Eris is more than 40 Astronomical Units (AU) from the Sun (see the discoverers and discovery dates in the dwarf planet's articles). These dwarf planets are also known as minor planets.

SatellitesEdit

The satellites of the planets are the smallest bodies in the Solar System (despite the dwarf planet, Pluto, being smaller than Earth's Moon). This definition is sometimes irrelevant though. Ganymede, the largest moon in the Solar System, is larger than the planet of Mercury. The Earth's moon is the largest natural satellite in the Solar System, being only a fourth smaller than its home planet, Earth. Yet, most of Jupiter's moons are asteroids from the Asteroid belt or loose asteroids from the same region.

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