All the controversy ended and all the wars and quarrels between astronomers over whether or not a number of Kuiper belt objects were planets were over. Pluto was removed from the list of planets by a new criterion presented at the meeting of the International Astronomical Society. Pluto is a distant object that has been discovered for more than 70 years, but the fate of this icy world, which until recently was known as the ninth planet in the solar system, removed from the orbit of the planets.
Pluto was removed from the list of planets in the solar system because it failed to meet one of the three conditions for being a planet. At the last meeting of the International Astronomical Society, it was confirmed that a space object would be called a planet if it orbited primarily a star. The second condition states that it must have sufficient mass to achieve hydrostatic equilibrium. The implication of this condition is that only objects with a spherical shape can expect to be a planet.
Pluto had the first two conditions, but because it was a member of the Kuiper belt, it could not meet the third condition and was therefore removed from the list of planets in the solar system . In this controversial meeting, the International Astronomical Society not only determined the characteristics of a planet, but also introduced new definitions in order to avoid future problems. In this session, the non-stellar objects of a system were divided into three categories, which are as follows:
- Planet: A object that orbits a star, has reached hydrostatic equilibrium, is not in the asteroid belt, and is not orbiting a planet like a moon.
- Dwarf planets: A group of objects that are in the asteroid belt has reached hydrostatic equilibrium, that is, they are spherical in shape, and the moon is not considered a dwarf planet.
- Objects of the third group: The members of this group include all moons (moons), asteroids, and small and large rocks in the interplanetary space and in general all the small objects of a stellar system.
Now all the controversy is over and the solar system, which was supposed to have several new planets, became an eight-planet system with the loss of one old planet. The decision of the International Union of Astronomers, which led to the removal of Pluto from the list of planets in the solar system, provoked the anger and reaction of some of the world’s leading astronomers.
According to the BBC: Dr. Allen Stern, NASA senior scientist who is leading the “New Horizons” space mission to Pluto, has said in a strong reaction that this decision is a shame. Mr. Stern, who did not take part in the vote, rejected the new definition of a planet that removed Pluto, saying it was incorrect. He was not present at the polling station.
On the other hand, voting was not possible electronically and this has caused criticism among astronomers. Dr. Stern, a well-known NASA scientist who recently launched the New Horizon spacecraft to Pluto, has said that he and some astronomers are seeking a request to return Pluto to the list of planets in the solar system by changing the definition of the planet. The decision of the International Astronomical Union has been ridiculed in some online circles.
The International Union of Astronomers has been the official reference for designations in the world of astronomy since 1919. Of the 2,500 astronomers present at the summit on Thursday, only 424 remain in Prague. Pluto is much farther and smaller than the eight planets in the solar system and orbits the sun on a different plane from the other planets. Experts have long disagreed on whether Pluto deserves the title of planet. Astronomers at the summit described Pluto as a small “ice dwarf” planet.
The issue of Pluto being removed from the list of planets in the solar system became more acute when another object beyond Pluto and larger, called 2003 UB313, was discovered by an American astronomer. After observing the 2003 UB313 by the Hubble Space Telescope, it was discovered that this celestial body is larger than Pluto and has a diameter of 3,000 kilometers. The new decision of these astronomers will cause many changes in textbooks and encyclopedias. The solar system after these changes includes eight planets, namely Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.