Almost 6,000 million km from the Sun "was" the ninth planet of the Solar System, Pluto. It is still there, but it no longer has the category of planet.
Pluto was discovered in 1930, invisible to the naked eye. In 1978 it was discovered that Pluto had a satellite of 1,186 km in diameter, Charon, whose mass is about 15% of that of the planet.
In the General Assembly of the International Astronomical Union (UAI) held in Prague on August 24, 2006, a new category called plutoid was created, which includes Pluto.
Astronomers had been trying to agree on a definition for years, after discovering UBS313 in 2003, located 14.550 million kilometers from Earth, which raised the problem of whether or not to be recognized as a planet, given that it is larger than Pluto.
Pluto was the smallest of the planets of the Solar System (it is two thirds the size of the Moon) and its orbit is inclined 17 ° with respect to the plane of the Earth's orbit (ecliptic), that is, an inclination greater than that of any other planet. Too many exceptions to belong to such a select club.
The study of the Solar System beyond Pluto is complicated due to the enormous distances. It is known that there are relatively large bodies. Quaoar and Sedna, recently discovered, have considerable sizes.
The Kuiper Belt is a distant area of the Solar System located beyond Neptune where a large number of asteroids are found, some of them up to 100 km in diameter. From the observations made, there may be more than 30,000 objects concentrated in a ring with a thickness of a few degrees around the ecliptic.
Finally, well beyond Pluto is the Oort cloud, a gigantic space eventually populated by asteroids and comets, some of which are propelled into the inner Solar System.
In this chapter:Pluto is a dwarf planet: Pluto is the smallest planet (now moemento, ex-planet or dwarf planet) and the one that moves farther away from the Sun ... Read pageThe Kuiper Belt: In 1951 the astronomer Gerard Kuiper postulated that it should exist a kind of proto-comet disc, a… Read page Candidates for planets (transneptunians): Scientists continued for years the search for a hypothetical planet X, which… Read page Comets, what they are and where they come from: Primitive men already knew Comets The brightest ones look great and I don't know… Read page Famous kites: Although there are many known kites, some have become more famous than others for various reasons… Read page The Oort Cloud: The Oort Cloud is a hypothetical set of small bodies astronomical, especially asteroids and comets, located ... Read pageExploration of space: Until the twentieth century, the idea of traveling through space was a thing of scientists too advanced or ... Read page