Scientists continued for years the search for a hypothetical planet X, which would occupy the ten place (X in Roman numerals), which could not be located, but whose presence would justify certain anomalies in the orbit of Pluto. There is no planet X, but in this way the Plutinos were discovered.
Plutinos are called the objects of the Solar System that, rotating around the Sun, are in 3: 2 orbital resonance with Neptune, that is, they complete two orbits around the Sun at the time that Neptune performs exactly three. This name is applied by the dwarf planet Pluto, which is also found in 3: 2 orbital resonance with Neptune. The term "transneptunians", more general, applies to all bodies beyond Neptune.
Like Pluto, these objects usually have quite elliptical orbits, such as Eris (described on the previous page), which often cross the path of Neptune, although they are never close enough to the planet so that there can be a collision hazard. The reason is that, due to orbital resonance, their relative positions are repeated cyclically.
Plutinos are asteroids composed mainly of ice and a core of rocky materials. It is estimated that approximately 40% of the objects that are beyond Neptune are Pluto, including Pluto itself. Based on extrapolations on the explored surface, it is estimated that there are more than 10,000 plutinos with a diameter greater than 100 km.
From Pluto to the heliopause there is a lot of distance, occupied by bodies of different sizes, very difficult to detect. However, increasingly precise instruments allow the progress of investigations.
In 2002, a celestial body (provisionally baptized as Quaoar) of about 1,300 km in diameter was identified within the Kuiper belt, the largest found orbiting the Sun since Pluto was discovered in 1930.
Quaoar is orbiting at a distance just slightly larger than that of the most distant planet in the Solar System. The large asteroid moves in relation to the background stars in the images of the discovery, taken by the Oschin Telescope in Palomar, California.
Quaoar, the name suggested by the discoverers of the cosmic rock, is one of several large asteroids that have recently been discovered wandering in the distant Kuiper Belt. Quaoar's size was determined from images from the Hubble Space Telescope. Quaoar is probably a cold world covered with ice, from which the Sun looks like a particularly bright star, nothing more.
Sedna, The Tenth Planet of the Solar System?
Sedna revolves around the Sun at a much greater distance than other stars in the system. Although its size is still uncertain, Sedna was once the largest of the bodies located around the Sun since the discovery of Pluto in 1930. This made him a candidate for a planet.
It is more than 10,000 million kilometers from Earth in the region called the Kuiper Belt, which has hundreds of known objects, small rock and ice worlds, although some may be as or larger than Pluto.
Sedna is redder than any other body of the Solar System, except Mars, and follows a very elliptical orbit, which at its furthest point puts 135,000 million kilometers from the Sun. Therefore, Sedna needs 11,500 Earth years to complete an orbit .
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