Why Pluto is no longer one of the nine planets of the solar system

Pluto, discovered in 1930 by the American astronomer Tombaugh, was named a large planet because he misestimated the mass of Pluto and thought that Pluto was larger than the Earth. However, after nearly 30 years of further observation, it was found that its diameter was only 2,300 kilometers, which was smaller than that of the Moon.

At the same time, new astronomical discoveries continue to call into question the traditional notion of the "Nine Planets". Astronomers have discovered some differences between Pluto and other planets in the solar system. Pluto is in orbit beyond Neptune, in the Kuiper Belt on the outer part of the solar system, an area that has long been the birthplace of the solar system's asteroids and comets.

Since the 90s of the 20th century, astronomers have discovered that Kuiper has more large bodies orbiting the sun. For example, the American astronomer Brown discovered "2003UB313", which is a celestial body with a diameter and mass greater than Pluto.

The discoveries of Brown et al. have brought great challenges to the traditional definition of planets. The new definition of planets, adopted by the General Assembly of the International Astronomical Union, is intended to bridge the gap between the traditional concept of planets and new discoveries.

The new definition of a planet includes two things: first, a planet must be a celestial body orbiting a star; The second is that the mass of the planet must be large enough, and its own gravity must be balanced with the surface force to make it spherical in shape. In general, the diameter of the planet must be more than 800 kilometers and the mass must be more than 5 billion tons.

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The latest draft limits the definition of planets to the solar system. According to the draft, "planets" are celestial bodies orbiting the Sun, whose gravitational pull is sufficient to overcome their rigid physical strength to make a celestial body spherical and capable of clearing other objects in the vicinity of its orbit. These include Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune, all of which were discovered before 1900.

Celestial bodies that also have sufficient mass and are spherical in shape, but cannot clear other objects in the vicinity of their orbits are called "dwarf planets".

Pluto was automatically downgraded to a "dwarf planet" because its orbit intersected Neptune's orbit and did not meet the new definition of a planet.

In addition to identifying Venus, Saturn, Jupiter, Mercury, Earth, Mars, Uranus, and Neptune as classical planets, Pluto was downgraded to a second-order planet, and the plan to add Ceres, Charon, and 2003UB313 as second-class planets was aborted.

The International Astronomical Union (IAU) relinquished the idea that the eight planets of the solar system other than Pluto were "classical planets", thus confirming that there were only eight planets in the solar system and that Pluto had been downgraded to a "dwarf planet". The first plan that was previously rumored proposed that the solar system would be aborted with plans to add three more second-order planets.

In 1930, the American astronomer Tombo discovered Pluto, and at that time misestimated the mass of Pluto, thinking that Pluto was larger than the earth, so he named it a large planet. However, after nearly 30 years of further observation, it was found that its diameter was only 2,300 kilometers, which was smaller than that of the Moon.

A planet must meet three conditions: it must be the largest object in the region; It must have a large enough mass to be able to rely on its own gravity to achieve an approximate spherical shape through hydrostatic equilibrium; Nuclear fusion reactions cannot occur inside celestial bodies. According to this scheme, in the solar system, only eight celestial bodies in the solar system, including Venus, Saturn, Jupiter, Mercury, Earth, Mars, Uranus, and Neptune, are confirmed as large planets, and Pluto is not among the large planets.

Pluto is defined as a dwarf planet.

Do you know why Pluto is not a planet? What is the reason that the nine planets of the solar system have become eight planets? Before 2005, everyone thought that our solar system had nine planets, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and of course, Pluto.

Pluto is the smallest of all these celestial bodies. Pluto was discovered by an American astronomer in 1930, and since then, everyone in the world has known the nine planets.

But one day in August 2006, scientists gathered at the International Astronomical Union in Paris and declared that Pluto was not a planet, which shocked the world and Pluto was removed from it. Now the question arises, why is Pluto no longer a planet? According to the International Astronomical Union, for a celestial body to become a planet, it needs to meet three basic criteria.

Firstly, the celestial body should revolve around the sun, secondly, the celestial body should be spherical, and thirdly, the area around its orbit should be clean and there should not be any celestial bodies of equal size or larger. This means that with the help of its gravitational pull. On this planet should be cleared of asteroids and dwarf planets on its side.

The planet is a planet because it is the dominant gravitational body in this orbit (other objects in and around the planet's orbit should be centered on the planet), but Pluto does not meet this criterion, and there are many Pluto-like objects in and around the orbit of Pluto, and the mass is not much different from that of Pluto. Pluto is only twice as massive as the other objects in its orbit. If Pluto can be considered a planet, then other celestial bodies inside and outside this orbit should also qualify.

Pluto is lovely and orbits the sun. Yes, he did meet the first two conditions, but scientists found that it did not meet the third criterion because it did not clear the adjacent celestial bodies around its orbit, therefore, it could not be called a planet and was downgraded to a dwarf planet. Since then, Pluto has not been among the planets of the solar system, and the nine planets have become eight planets.

This is because Pluto is not in the same orbit as other planets, and it is far away from other planets. I cannot connect it.

Pluto was first discovered as a planet, but later on, based on repeated observations by astronomers, it was found that it was too small, even smaller than some moons, so it was not classified as a planet.

The reason why Pluto is not a planet is because it has been shrinking and has shrunk to the size that it should be when it exits the planet, so it is judged not to be a planet.

Because Pluto is mostly liquid rather than solid, and Pluto is too far away from the Sun and does not need to depend on the Sun to survive at all.