A few years ago, our solar system had nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Pluto. But today it is made up of only eight planets. These can be classified into two groups: the first four rocky inner planets and the next four gas giants, the two groups being separated by the asteroid belt. Pluto, the former ninth planet of the solar system, was excluded from the list of planets in 2006 by the International Astronomical Union (IAU). What forced the IAU to take this step. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essayPluto was discovered in 1930 by American astronomer Clyde Tombaugh. It was known as the smallest planet in the solar system. Among the nine planets known at that time, Pluto's orbit was the most elliptical, while Mercury was the second most elliptical. On average, the distance from the Sun is 39 AU. Its orbital period is 248 years. In 1978, Pluto's first satellite, "Charon", was discovered, and it was found that Pluto and Charon rotate around their common center of mass and therefore can be treated as a binary planetary system. The history of the nine planets has remained so for more than 70 years. years. In 2005, with the discovery of Eris (which will be the tenth planet), Pluto's planet status came into danger. As had been predicted, there are a large number of such objects orbiting the Sun in the outer region of the solar system (now known as the Kupier belt). The Kupier Belt (KB) is a disk beyond Neptune and up to 50 AU from the Sun, just like the asteroid belt between Mars and Jupiter, but much larger and more massive than it. Trillions of things are present in this KB. Almost all composed of "ice" (frozen methane, water, ammonia, etc.) and rocks. So the discovery of Eris and the prediction of many of these objects led the IAU to redefine the term “PLANET”. This step was taken in fear of having 40-50 planets in our solar system in the next few years. In the 26th general assembly of the IAU held in 2006, a planet is redefined as: A planet is a celestial body that (i) is in orbit around the Sun, (ii) has sufficient mass for its gravity to acquire a spherical shape and (iii) cleared the area around its orbit. Pluto follows the first two criteria since it is round and orbits the Sun. However, it does not follow the third criterion. This is clear from the fact that Pluto has only 0.07 times the mass of everything else in its orbit, while Earth has 1.7 million times the mass of everything else in its orbit. Please note: this is just an example. Get a custom article sample now from our expert writers. Get a Custom Essay So after redefining a “Planet”, Pluto and Pluto-like objects cannot be in the list of planets. At the same time that Pluto was demoted from being a planet, the IAU officially announced a third category of planets known as “dwarf planets”.”.