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Dysnomia is a solar system dwarf planet moon.

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Dysnomia, officially designated (136199) Eris I Dysnomia, is a moon of the Dwarf planet Eris. Dysnomia was discovered in 2005 by Mike Brown and the laser guide star adaptive optics team at the W. M. Keck Observatory, and carried the provisional designation of S/2005 (2003 UB313) 1 until officially named Dysnomia (from the Greek word meaning "lawlessness") after the daughter of the Greek goddess Eris.

Discovery of Dysnomia moon.

Dysnomia moon.
Eris and Dysnomia: artist's impression.
Discoverer M. E. Brown,
M. A. van Dam,
A. H. Bouchez,
D. Le Mignant
(using the Keck Observatory)
Discovery date 10 September 2005
Orbital characteristics
Semi-major axis (a) 30,000 - 36,000 km
eccentricity 0?
Orbital period (P) ~14 d
inclination unknown
Parent body Eris
Physical characteristics
Mean diameter 300 - 400 km

During 2005, the adaptive optics team at the Keck telescopes in Hawaii carried out observations of the four brightest Kuiper belt objects (Pluto, 2005 FY9, 2003 EL61, and Eris), using the newly commissioned laser guide star adaptive optics system. Observations taken on 10 September revealed a moon in orbit around Eris, it was provisionally designated S/2005 (2003 UB313) 1. In keeping with the Xena nickname that was already in use for Eris, the moon was nicknamed "Gabrielle" by its discoverers, after the television warrior princess's sidekick. Also, Xena's character was played by actress Lucy Lawless, whereas Dysnomia is the Greek goddess of lawlessness.

Properties of Dysnomia.

The satellite is about 60 times fainter than Eris, and its diameter is estimated to be approximately eight times smaller. With only a single observation, the satellite cannot yet be used to measure or constrain the mass of Eris, but likely orbital parameters were nevertheless estimated. One of these is its orbital period, thought to be about two weeks (14 days). Further observations made with the Keck telescopes in August and September 2006 have led to a much better measurement of the period. Once astronomers refine the period and the Semimajor axis of the satellite's orbit (currently estimated at 36,000 km), they will be able to determine the mass of the system.

Formation of Dysnomia moon.

Astronomers now know that three of the four brightest kuiper belt objects (KBOs) have satellites, while among the fainter members of the belt only about 10% are known to have satellites. This is believed to imply that collisions between large KBOs have been frequent in the past. Impacts between bodies of the order of 1000 km across would throw off large amounts of material which would coalesce into a moon. A similar mechanism is believed to have led to the formation of Earth's own Moon when the Earth was struck by a giant impactor early in the history of the Solar System.

Further reading about the solar system.
The Sun Mercury Venus Earth Mars Ceres Jupiter Saturn Uranus Neptune Pluto Eris
Planets Dwarf planets Moons: Terran Martian Asteroidal Jovian Saturnian Uranian Neptunian Plutonian
Small bodies:   Meteorites Asteroids (Asteroid belt) Centaurs TNOs (Kuiper belt/Scattered disc) Comets (Oort cloud)
Solar system related pages. astronomical objects and the solar system's list of solar system objects.

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