Here they are in order from the Sun, with the planets numbered, and the dwarf planets marked with the letters a to e. There are a few main parts of the Solar System. These small planets are sometimes called plutinos. Instead they defined a new category of dwarf planet, into which Pluto did fit, along with some others. After this, Pluto was put on the list of minor planets and was downgraded in 2006 by astronomer Michael E Brown. It became a "dwarf planet" along with Eris and many others. By this definition, Pluto was not a planet anymore due to its irregular orbit and size. This all changed on August 24, 2006, when the International Astronomical Union (IAU) decided on the correct definition for the word "planet" for the first time. Pluto was discovered by American astronomer Clyde Tombaugh and was declared the 9th planet of the solar system in 1930. Mercury has a more elliptical orbit than the others, and some of the smaller objects orbit the Sun in very eccentric orbits.ĭiscovery and exploration The other planets in the Solar System also orbits the Sun in slightly elliptical orbits. The Earth's orbit around the Sun is nearly a perfect circle, but when mapped it is found that the Earth moves around the Sun in a very slightly oval shaped orbit, called an elliptical orbit. This planetary migration is thought to have been responsible for much of the Solar System's early evolution. In the early stages, the positions of the planets sometimes shifted, and planets have switched places. Many collisions between bodies have occurred, and have been important to the evolution of the Solar System. Still others, as the Earth's Moon, may be the result of giant collisions. Many moons have formed from circling discs of gas and dust around their parent planets, while other moons are believed to have formed and were later captured by their planets. The Solar System has evolved considerably since its initial formation. As our knowledge of space has grown, the models have been changed to account for the new observations. It has been adjusted by scientific disciplines such as astronomy, physics, geology, and planetary science. This model, known as the nebular hypothesis, was developed in the 18th (1700s) century by Emanuel Swedenborg, Immanuel Kant, and Pierre-Simon Laplace. Most of the collapsing mass collected in the centre, forming the Sun, while the rest flattened into a protoplanetary disk of loose dust, out of which the planets, moons, asteroids, and other Solar System bodies formed. The formation and evolution of the Solar System began 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Main article: Formation and evolution of the Solar System Most of the billions of stars in the Milky Way galaxy might have a planetary system. Many other systems like the Solar System have been found. The largest moon is Ganymede which is a moon of Jupiter.įurthermore, planetary dust orbits the gas giants. Mercury and Venus have no moons, and Jupiter and Saturn have the largest number of moons. There are about 200 moons in the Solar System. Six of the planets and three of the dwarf planets are orbited by moons. He is sometimes known as the "Greek Copernicus". In Ancient Greece, Aristarchus of Samos proposed the heliocentric model of the Solar System, where the Sun, is at the center of the known universe. There are also comets, centaurs, and interplanetary dust. There are thousands of very small objects in these areas. These areas have dwarf planets, including Pluto, Makemake, Haumea, Ceres and Eris. Further out than Neptune, there is the Kuiper belt and the scattered disc.
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There are asteroid belts, mostly between Mars and Jupiter. The Solar System also contains other things. Titan, one of Saturn’s moons, is the only moon in the solar system to have an atmosphere.
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This is because they are much larger than other planets and are mostly made of gas. The last four planets are called gas giants. They are mostly made of rock and metal, and they are mostly solid. The first four planets are called terrestrial planets. From closest to farthest from the Sun, they are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. There are eight planets in the Solar System. The Sun is mostly made out of hydrogen, and some helium and higher elements. The other objects are pulled into orbit around the Sun. It makes up 99.9% of the Solar System's mass. It is thought that almost all stars form by this process. Most of this matter came together in the center, and the rest flattened into an orbiting disk that became the Solar System. It formed by gravity in a large molecular cloud. The Solar System is about 4.6 billion years old. The Sun is orbited by planets, asteroids, comets and other things. The Solar System is the Sun and all the objects that orbit around it. A simple video explanation of the Solar System