Eris

Eris dwarf planet

Eris, the object 2003 UB313, was officially named by the International Astronomical Union in August 2006. The name chosen is the Greek goddess Eris. In Greek mythology, Eris is the goddess of Discord. According to Hesiod, she is the daughter of Nyx (Night) and mother of Pain, famine and other scourges.
The choice of the names Eris and Dysnomia, daughter, goddess of anarchy suggests, first, the fierce discussion and controversy among scientists about the questioning of the definition of the word "planet", and secondly , the apparent diversity of the orbits of objects scattered in this zone of the solar system, contrary to regular orbits of the planets of the solar system (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto). This object is located at more than twice the distance of Pluto from the Sun (97 AU) would be the size of Pluto. Astronomers assume that many other icy objects bigger than Pluto probably exist in the Kuiper Belt (located in the distant solar system. For the astronomer Mike Brown who discovered Eris in 2003 with the telescope on Mount Palomar, "it is very difficult to measure the size of objects in the outer Solar System but occultation of stars have the potential to respond extremely accurate." That of November 6, 2003 Eris back to a size between 2320 and 2350 km and the place behind Pluto (2370 km).
In 2007, a series of observations of the largest trans-Neptunian objects by the Spitzer Space Telescope has given Eris a diameter equal to 2326 km.

However, the uncertainty around the exact diameter of the two astronomers plutoids makes careful.
This object has an orbit inclined 44 ° to the ecliptic (Pluto's orbit is inclined 17 °) with a distance from the Sun ranging from 38 to 97 AU (30 to 49 for Pluto), an orbital period of 557 years (Pluto 249 years).

Image: 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.

Orbit of Eris

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.

Dysnomia, the moon of Eris

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.

Image: Orbit of Dysnomia around the planet Eris