Solar system is the whole system of the planets and other bodies that revolve around or orbit the ((Sun)) in its gravitational field. This system is called solar because of the Sun, from which it derives its name. This system not only includes the Sun together with the nine planets, their moons, and all other bodies that orbit it, but also asteroids, comets, meteoroids, and Kuiper belt objects. The outer limit of the solar system is formed by the heliopause. In fact this Solar or Sun's system contains billions of other objects and extends far beyond the outermost planets. As per latest astronomical evidence, several hundred thousand asteroids revolve around the Sun in orbits mainly between Mars and Jupiter. The number of smaller meteoroids, including cometary debris and fragments from the collision of larger bodies are countless. In addition, billions of objects, most of them having sizes of a speck of dust, cross through our atmosphere as meteors or micrometeoroids each day, though most of them are invisible to us. Billions more lie in the area surrounding the solar system, in the disk of debris known as the Kuiper belt and in the swarm of comets known as the Oort cloud. There are nine planets in our Solar system which we traditionally think to be true. However, the findings of the objects in the Kuiper belt, discovered in the 1990s have undermined the status of Pluto as the ninth outermost planet of the Solar system. A controversy began when the new planetarium at the American Museum of Natural History opened in 2000, gave opportunities to peep into the mysteries of the universe. Many visitors were shocked to find there that Pluto had been demoted to a Kuiper belt object. Despite this, for most of us there are yet nine planets in our Solar system which are ((Mercury)), ((Venus)), ((Earth)), ((Mars)), ((Jupiter)), ((Saturn)), ((Uranus)), ((Neptune)), and ((Pluto)). There are also four dwarf planets in our Solar system knows as plutons. They are Eris, Pluto, Charon, and Ceres. They are small distant planets that take more than 200 years to orbit the sun. It is believed that this planetary system was formed 4•6 thousand million years ago as a by-product of the Sun's formation. There is no doubt that the Mercury is the closest to the sun. However, there is a debate about which planet is the farthest, Neptune or Pluto. Pluto, for most of its orbit, is farthest. However, its path is highly eliptical or stretched out. At its closest approach to the sun it is 4.4 billion kilometres away while at its farthest approach it is 7.3 billion kilometres away. This is why, Neptune claims ninth planet from the sun whenever Pluto's path crosses inside Neptune's. Otherwise, it is eighth planet from the sun during the cycle of 228 years. Almost 20 years is a period when Neptune is the farthest planet of the solar system. Such a recent period was between 1979 and 1999.
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