Dwarf planets

automatic translation

"A planet is a celestial body which is on orbit around the Sun, which possesses a sufficient mass so that its gravity takes it on the strengths of cohesion of the solid body and maintains it in hydrostatic equilibrium (spherical shape), and which eliminated any body moving on a close orbit ".
This definition was approved on August 24th, 2006, during the 26th General assembly of the UAI (International Astronomical Union) by a vote by a show of hands about 400 scientists and astronomers after ten days of discussions.
In addition, the UAI created a new class of objects: the dwarf planets. A dwarf planet, since the new definition of August, 2006, is a celestial body on orbit around the Sun:
- witch has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (near-spherical) shape,
- witch has not cleared the neighborhood around its orbit.
- witch is not a satellite
According to this last one, three bodies reach the status of dwarf planet: Pluto, Eris, and Ceres. Other bodies should soon join this nomenclature.

* Representation of the largest trans-Neptunian objects known from the Earth. The four biggest: Eris, Pluto, Makemake and Haumea were granted the status of dwarf planet.

Pluto

category : planet

Pluto 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.  was discovered in 1930 during the search for a celestial body allowing to explain the orbitales disturbances of Uranus and Neptune, hypothesis proposed by Percival Lowell as being the Planet X. Pluto possesses a satellite, 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.

Eris

category : planet

Eris The object 2003UB313, is officially appointed by the international astronomical Union in August, 2006. The name chooses is that of the Greek goddess Eris. In the Greek mythology, Eris is the goddess of the Discord. According to Hésiode, she is a girl of Nyx (the Night) and a mother of the Pain, the Famine and the other plagues  was photographed for the first time during made observations in October 21st, 2003 with the telescope Oschin of 1,22 meters of the Mountain Palomar, in California, by the team of Caltech was photographed for the first time during observations made which had already discovered several big beyond Neptune objects as (50000) Quaoar and (90377) Sedna.
Thanks to the spatial telescope Hubble and to that of the W.M. Keck Observatory the measure of the mass of Eris, the biggest member of the class of dwarfish planets in our Solar system, was able to be realized. Eris is 1,27 times as massive as Pluto, formerly the biggest member of the Belt of Kuiper of the ice-cold objects revolving beyond the orbit of Neptune.

Ceres

category : planet

Ceres Ceres is the first bare asteroid. We recognize him the definition of dwarfish planet today, since the new definition of the international astronomical Union of August, 2006. With about a diameter 950 km, Ceres is also the biggest member of the belt of asteroids situated between the orbits of Mars and Jupiter was accidentally discovered.
Piazzi tried to observe a star listed by Francis Wollaston under the name of Mayer 87 because she was not in the position given in the zodiacal catalog of Mayer (it turned out afterward that it was in fact about Lacaille 87).
On the place, he observed an object moving on the sky, that he believed at first to be a comet.

Sedna

category : planet

Sedna Sedna (Goddess Inuit of the ice-cold oceans of the north pole), is the biggest beyond Neptune object after Pluto and Eris.   Situated in an almost empty space, Sedna is more red and more brilliant than any object of the solar system. The scientists have not determined the reason of these unique characteristics yet. He could possess the small moon. In April, 2005 a more precise measure of the celestial body allowed to determine a complete rotation speed about 10 hours. At the time of its discovery, Sedna was the biggest object discovered in the solar system since the discovery of Pluto. Bigger objects (dwarf planets) were since discovered, as Eris.

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Astronomy - october 15th 2007