Dysnomia (moon)
Moon of Eris / From Wikipedia, the free encyclopedia
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Dysnomia (formally (136199) Eris I Dysnomia) is the only known moon of the dwarf planet Eris and is the second-largest known moon of a dwarf planet, after Pluto I Charon. It was discovered in September 2005 by Mike Brown and the Laser Guide Star Adaptive Optics (LGSAO) team at the W. M. Keck Observatory. It carried the provisional designation of S/2005 (2003 UB313) 1 until it was officially named Dysnomia (from the Ancient Greek word Δυσνομία meaning anarchy/lawlessness) in September 2006, after the daughter of the Greek goddess Eris.[6]
Discovery | |
---|---|
Discovered by | Brown et al.[lower-alpha 1][1] |
Discovery date | 10 September 2005[1] |
Designations | |
Designation | Eris I |
Pronunciation | /dɪsˈnoʊmiə/, /daɪˈsnoʊmiə/[lower-alpha 2] |
Named after | Δυσνομία Dysnomia |
S/2005 (2003 UB313) 1 Dy /ˈdaɪ/ (nickname) Gabrielle (nickname) | |
Adjectives | Dysnomian |
Orbital characteristics[2]: 5 | |
Epoch 31 August 2006 (JD 2453979.0) | |
37273±64 km | |
Eccentricity | 0.0062±0.0010 |
15.785899±0.000050 d | |
Average orbital speed | 0.172 km/s[lower-alpha 3] |
Inclination | ≈ 0° (to Eris's equator; assumed) 78.29°±0.65° (to Eris's orbit) 45.49°±0.15° (to celestial equator) 61.59°±0.16° (to ecliptic)[lower-alpha 4] |
126.17°±0.26° | |
180.83°[lower-alpha 5] | |
Satellite of | Eris |
Physical characteristics | |
Mean diameter | 615+60 −50 km[3]: 7 |
Mass | (8.2±5.7)×1019 kg[3]: 6 |
Mean density | 0.7±0.5 g/cm3[3]: 7 |
synchronous[4] | |
≈ 0° to orbit (assumed) | |
Albedo | 0.05±0.01[3]: 7 |
25.4[lower-alpha 6] | |
5.6[lower-alpha 6] | |
With an estimated diameter of 615+60
−50 km, Dysnomia spans 24% to 29% of Eris's diameter. It is significantly less massive than Eris, with a density consistent with it being mainly composed of ice.[3]: 8 In stark contrast to Eris's highly-reflective icy surface, Dysnomia has a very dark surface that reflects 5% of incoming visible light,[3] resembling typical trans-Neptunian objects around Dysnomia's size.[7] These physical properties indicate Dysnomia likely formed from a large impact on Eris, in a similar manner to other binary dwarf planet systems like Pluto and Orcus, and as well as the Earth–Moon system.