Discovered in 1930 by the American astronomer Clyde Tombaugh, Pluto is out of the ordinary. Of an equatorial diameter lower than 2 500 km, it represents only tenth two of the Earth. Not satisfied to be, so far, the smallest member of the solar system, it also possesses an eccentric and very oblique orbit with regard to the plan of the ecliptic. Sometimes even, Pluto is closer of the Sun that Neptune. It is crossed in the perihelion Near the Sun. It is the point the closest to the Sun in the orbit of a planet. in 1989, its passage in the aphelion Far from the Sun. It is the point the most remote from the Sun in the orbit of a planet. is planned for 2113. Pluto is the second dwarfish planet of the solar system by the size.

It orbits around the Sun at a distance varying between 29 and 49 astronomical units and belongs to the belt of Kuiper. It is about the first trans-Neptunian object of having been discovered. The solar system, which counted nine planets since 1930, contains no more than eight since August, 2006. Further to this modification of the nomenclature, Pluto was added to the list of the minor objects of the solar system and saw attributing the number 134340 in the catalog of the minor objects.

The solar system lost one of the members of the family of planets. International Astronomical Union ( IAU) integrated the new family of the dwarfish planets. The first suspicions on the real nature of Pluto were born in 1992. This year, the American David Jewitt and Jane Luu observed for the first time an object of the belt of Kuiper.

The existence of such objects, little brilliant and revolving beyond Neptune, was suggested by Gerard p. Kuiper in 1951. Of a diameter of some hundreds of kilometers, it would be about rests of the original nebula which gave birth to the solar system. Now, the advent of telescopes always more powerful during these last five years allowed the discovery of about seventy objects of this type.

The satellites of Pluto

category : dwarf planets

Charon, discovered by James Christy in 1978, is a big satellite with regard to the planet mother (diameter 1270 km). Charon has a mass about ten times lower than Pluto and the report of diameters is from 1 to 2. The infernal couple turns around its common centre of gravity, as two objects connected by a stiff bar such a barbell. Charon is situated in only 19000 km of the dwarf planet and moves around this planet with a period of 6,4 days (equal to the period of rotation of Pluto, what establishes a geostationary orbit).

Hydra Hydra is the mythological snake in nine heads which kept the realm of Pluto which is the Roman name of the Greek god of the Hells, Hades. Besides the relation with Pluto, names were chosen because of their initials "N" and "H", which are also the first letters of New Horizons, the probe of the NASA launched in January, 2006 towards the system of Pluto.  and Nix In the Greek mythology, Nyx was the night goddess and the mother of Charon, the man who transported in his boat souls through the river the Styx towards the underground world governed by Pluto. THE UAI modified its name in "Nix" according to the Egyptian spelling of the name of the goddess to avoid any confusion with two asteroids which already carry the name "Nyx".  are two small satellites discovered on orbit around Pluto, thanks to the spatial telescope Hubble in May and June, 2005 by two American astronomers Alan Stern and Hal Weaver. Two new moons orbit to 44000 km of Pluto, is twice farther than Charon. They make between 45 and 160 km in diameter and are 5000 times less brilliant than Charon. Both satellites circulate in the plan of Charon. They were cataloged under the temporary references S / 2005 P1 and S / 2005 P2, before becoming Hydra and Nix in 2006.

Photo taken by Hubble on May 15th, 2005.