| File:2006-16-a-full.jpg Eris and Dysnomia: artist's impression | |
| Discovery | |
|---|---|
| Discoverer | Michael E. Brown (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 |
Dysnomia, officially designated (136199) Eris I Dysnomia, is a moon of the dwarf planet Eris. It was discovered in 2005 by Mike Brown, and carried the provisional designation of S/2005 (2003 UB313) 1 until officially named Dysnomia (a Greek word which means "lawlessness") after the daughter of the Greek goddess Eris.
Discovery
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. Coincidentally, Dysnomia means "lawlessness," while the character of Xena was played by an actress named Lucy Lawless.
Properties
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 to be made with the Keck telescopes in August 2006 will allow 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[1]), they will be able to determine the mass of the system.
Formation
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.
References
- ^ Michael E. Brown (2006). "Satellites of the largest Kuiper belt objects" (PDF). Astrophys.J. 639 (L43). arXiv:0510029
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