Eris

This article is about the Dwarf Planet named Eris. For the classical goddess, see Eris (mythology). For any other use, see Eris (disambiguation).

Eris
Date of discovery	October 21, 2003[1]
Name of discoverer	Michael E. Brown[1][2][3]
Name origin	Greek goddess of discord[2]
Orbital characteristics
Primary	Sun
Order from primary	12
Perihelion	37.93 AU[4]
Aphelion	97.53 AU[4]
Semi-major axis	67.732 AU[4]
Titius-Bode prediction	154 AU[5]
Orbital eccentricity	0.4400[4]
Sidereal year	557.4 a[4]
Avg. orbital speed	3.436 km/s
Inclination	44.1595°[4] to the ecliptic
Rotational characteristics
Sidereal day	8 h
Physical characteristics
Mass	1.66 * 1022 kg[4][6][7]
Density	2,260 kg/m³[4]
Mean radius	1,300 km[8]
Surface gravity	0.6554 m/s²[5]
Escape speed	1.305 km/s[5]
Surface area	21,237,166 km²[5]
Minimum temperature	30 K
Mean temperature	42.5 K
Maximum temperature	55 K
Number of moons	1
Color	white to light gray
Albedo	0.87[4]

Eris, also known as Xena, also known as 2003 UB₃₁₃, the largest of all dwarf planets (also classified as a plutoid), is named for the Greek goddess of discord and strife. Considering the debate that the discovery of this object provoked, the name is probably quite apt.

Discovery, Naming, and Debate[edit]

Eris was first photographed on October 21, 2003, but was at first too slow-moving for the Palomar Observatory image-analytic software to detect. Later, Michael E. Brown, Chad Trujillo, and David Rabinowitz ordered re-analysis of the images with greater sensitivity. They soon realized that the images depicted a new object, and announced their findings on January 5, 2005.

The initial name for the new object was Xena, the title character in an American television action-adventure dramatic series,^[9] and also a name beginning with X, in keeping with the suspicion that this object was the long-sought "Planet X." The object also had a satellite, which the discoverers tentatively named Gabrielle, after the supporting character in that dramatic series.

The announcement of Eris' discovery on July 29, 2005 presented the International Astronomical Union with an embarrassing problem.^[10] Other observations, specifically of the period and orbital characteristics of the satellite,^[11][12] had already suggested that 2003 UB₃₁₃ might be more massive even than Pluto, then considered the ninth planet in the solar system. Because planets and Kuiper-Belt objects have different naming conventions, and because scattered disk objects had no naming convention at the time, the names for the new primary and satellite remained unofficial.^[13]

Finally the International Astronomical Union arbitrarily declared^[14] that Pluto and 2003 UB₃₁₃ were not planets, but belonged to a new category called dwarf planets. Then on September 6, 2006, Mike Brown and his team^[15] recognized that the name "Xena" was inappropriate for 2003 UB₃₁₃ and suggested to the IAU that they name it Eris, after the Greek goddess of discord and strife. They also suggested that the IAU name the satellite Dysnomia, for the Greek goddess of lawlessness and daughter of Eris.^[16] Four days later, the IAU officially named the primary Eris and named its satellite Dysnomia.^[17]

Earth and Mars as dwarf planets under the current International Astronomical Union definition[edit]

According to Number 1 (c) and 2 (c) of the IAU definition, also Earth and Mars wouldn't be planets because they haven't "cleared" their orbits as several asteroids are in their respective orbits, these asteroids are also called "quasi-moons" of Earth and Mars. The IAU precluded this possibility by arbitrarily listing the earth and mars as planets in spite of the current definition (see the quote in the section The dwarf planet controversy where it says "¹The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune."). This, however, calls into question the "scientific" basis of downgrading Pluto to a dwarf plant as this conflicting standard(of confirming earth and mars as planets while classifying Pluto as a dwarf planet) suggests it is merely the opinion of the IAU that Pluto is not a planet ^[18]

Orbital characteristics[edit]

At 67.7 AU from the Sun, it is the most distant object yet discovered that has the Sun for a primary. At aphelion, it is far beyond the Kuiper belt and in what is known as the scattered disk of the solar system. Because Eris is so distant from Earth (currently near aphelion and hence three times more distant than is Pluto as of 2008), it has a very long sidereal year of 557 Julian years. Its synodic year is very nearly the same as an Earth year.

Surface and atmosphere[edit]

Infrared spectroscopic scans of Eris reveal an infrared reflectance spectrum remarkably like that of Pluto, which is known to have a layer of methane on its surface. From this, the discovery team concludes that Eris is surfaced with solid frozen methane, with rock and water ice beneath.

Yet Eris is the second most reflective body in the entire solar system, reflecting about 86% of the incident sunlight. Eris is also uniformly white on its surface, whereas Pluto is a mottled brown. The discoverers believe that this is due entirely to Eris' present far-flung position (near aphelion), and point out that Eris' orbit is the most eccentric orbit of any satellite of the Sun, except for comets.

Implications for Other Trans-Neptunian Objects[edit]

Brown et al. noted^[3] in 2005 that Eris, Dysnomia's primary, is one of three of the four brightest Kuiper belt objects that have satellites. (The other two are Pluto and 2003 EL₆₁.) The fourth, 2005 FY₉, has no satellite that Earth-based telescopes can presently detect. Most Kuiper belt objects do not have satellites, and that three of the four brightest should have satellites suggests that their origins were significantly different from those of other Kuiper belt objects.

Problem for uniformitarian theories[edit]

Brown states^[6] that the near-circular orbit of Dysnomia about Eris actually is consistent with Dysnomia's origin as the result of a collision between Eris and another object. But no astronomer has ever explained how such a collision would leave an object in a nearly circular orbit about its primary.

Satellites[edit]

Eris has one known satellite, a tiny moon called Dysnomia. In classical mythology, Dysnomia is the name given to Eris' daughter, who is a symbol of actual lawlessness.

Observation and exploration[edit]

The Hubble Space Telescope and the Keck Observatory are the first two telescopes to observe the Eridian system. No deep-space missions are planned.

See Also[edit]

• The Dwarf Planet Controversy

References[edit]

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