Pluto was discovered on February 18, 1930, at the Lowell Observatory in Flagstaff, Arizona, by astronomer Clyde W. Tombaugh, with contributions from William H. Pickering. It was discovered as the ninth planet and was called ‘’Planet X”. But after some discoveries, it was believed that there are three types of bodies- planets, dwarf planets, and Small Solar System Bodies. Pluto is no more considered a planet, instead, it is a dwarf planet and some of us don’t know why.
The reason why Pluto is no more a planet is that according to the International Astronomical Unit (IAU), Pluto failed to meet the criteria of a full-sized planet. The three criteria of the IAU for a full-sized planet are It is in orbit around the Sun, has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), has “cleared the “neighborhood” around its orbit. Pluto meets only two of these criteria, losing out on the third. In all the billions of years it has lived there, it has not managed to clear its neighborhood. That means, “not clearing its neighboring region of other objects?”
This means that the planet has become gravitationally dominant, there are no other bodies of comparable size other than its satellites. So, any planet that does not meet these criteria is called a dwarf planet and Pluto is one of them.
Pluto is smaller than any other planet- even smaller than Earth’s moon. The scientists have believed it as a binary object in the solar system that originated elsewhere in space and got caught in the sun's gravity. Pluto is relatively round and orbits the sun, but it does not meet the criteria because its orbit crosses Neptune's orbit. There are arguments that other planets in the solar system, including Earth, have not cleared the neighborhood around their orbits. Earth, for example, regularly encounters asteroids in and near its orbit. But it is relatively large than the planet Pluto.
These facts contributed to the long-running debate over whether to consider Pluto a planet. And, hence, after all the discoveries and arguments, the scientists concluded, that Pluto can fall in the category of the dwarf planet but does not meet the criteria of falling under the category of planets. Therefore, Pluto is still there in the solar system. It’s just that it's not considered a planet anymore. This ends the debate if Pluto is still a part of the solar system.
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