Eris

The object 2003 UB313, 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 Hesiode, she is a girl of Nyx ( the Night) and a mother of the Pain, the Famine and the other plagues. The choice of the naming Eris and Dysnomie, her daughter, goddess of the anarchy evokes, on one hand, the discussions and the relentless controversies enter scientists on the questioning of the definition of the word "planet", and, on the other hand, the visible variety of the orbits of the scattered objects of this zone of the solar system, in contrario of the regular orbits of the planets of the solar system (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto). This object situated in more of twice the

distance of Pluto to the Sun ( 97 UA), would be 20 % bigger than Pluto. The astronomers suppose that the other numerous ice-cold objects bigger than Pluto exist probably in the Belt of Kuiper, localized in distant solar system. This object has a nearby diameter of 2700 km (Pluto is 2274 km one diameter), an oblique orbit of 44° on the ecliptic (Pluto has an oblique orbit of 17°), with a distance in the sun varying from 38 to 97 U.A (30 - 49 for Pluto), a period of revolution of 557 years ( 249 for Pluto).

Below a Juxtaposition of 3 images taken in 90 minutes of interval, on October 21st, 2003 (Look-out Observatory of the Mountain Palomar).

Eris (encircled by white) moves very slightly with regard to the bottom of stars. This so weak movement had not been noticed during the first observation in 2003, but in 2005.

category : dwarf planets

Eris is at present situated in 97 ua of the Sun and turns around this one in 557 years, according to a very oblique orbit, approximately 44°. its orbit is strongly eccentric affable and until 35 ua of the Sun in its perihelia (the distance of Pluto in the Sun varies between 29 and 49,5 ua, whereas Neptune orbits in 30 ua). Because of this orbit, Eris is a scattered object of the belt of Kuiper. Eris is at present in the constellation of the Whale.

During the announcement of its discovery in July, 2005, Eris was the most distant objects known in the solar system, even if about forty transneptuniens objects (as (90377) Sedna, (87269) on 2000 OO67, 2000 CR105 and (15874) on 1996 TL66), at present more close to the Earth, possess a half-main line centre widely bigger. Among the objects of the belt of Kuiper, it is classified third by its luminosity.

Orbital characteristics

category : dwarf planets

If the orbital characteristics are "rather easy" to obtain, the diameter of Eris is very difficult to measure, because even in the best telescopes, this object is only a point without dimension. What we measure easily, it is the luminosity. If we suppose that it is about a perfectly white body, of albedo 1, we can calculate a size, which will be a lower limit. This minimal size is 2200 km (very slightly lower than that of Pluto). If we give to this body a "usual" albedo for the ice-cold bodies ( 0,6 ), we obtain 2900 km one diameter.

2600 km proposed by Mike Brown correspond to an intermediate value. But if Eris is dark (as for example Charon, satellite of Pluto, with an albedo of 0,38), it would be even bigger (3550 km).

Drawing on the estimation of the sizes of objects claiming in statute of planet with regard to the Earth.

Dysnomie, the moon of Eris

category : dwarf planets

The astronomers of the Institute of Technology of California have just discovered that it possesses the moon. The moon, orbiting around the planet in the two weeks, was tracked down on September 10th, 2005, with the telescope of 10 meters Keck II du W.M. Keck Observatory to Hawaii by Michael E. Brown, professor of global astronomy, and his colleagues of the Caltech. Brown considers that the moon, the measure at least a tenth of the size of Eris, which is supposed be one diameter 2700 kilometers (2274 kilometers for Pluto).

This satellite is 60 times less brilliant than Eris, what allows to estimate its diameter at the eighth of this one, that is 300 in 400 kilometers. The orbital period of the satellite is not still exactly known, but estimated in 14 days.