Dysnomia (moon)

For other uses, see Dysnomia.

Dysnomia
Low-resolution image of Eris and Dysnomia as imaged by the Hubble Space Telescope, August 2006
Discovery
Discovered byBrown et al.[a][1]
Discovery date10 September 2005[1]
Designations
Designation
Eris I
Pronunciation/dɪsˈnoʊmiə/, /daɪˈsnoʊmiə/[b]
Named after
Δυσνομία Dysnomia
S/2005 (2003 UB313) 1
Dy /ˈdaɪ/ (nickname)
Gabrielle (nickname)
AdjectivesDysnomian
Orbital characteristics[2]: 5 
Epoch 31 August 2006 (JD 2453979.0)
37273±64 km
Eccentricity0.0062±0.0010
15.785899±0.000050 d
0.172 km/s[c]
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)[d]
126.17°±0.26°
180.83°[e]
Satellite ofEris
Physical characteristics
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)
Albedo0.05±0.01[3]: 7 
25.4[f]
5.6[f]

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]

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 the Earth–Moon system.


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  1. ^ a b Cite error: The named reference Brown2006-discovery was invoked but never defined (see the help page).
  2. ^ a b c Cite error: The named reference Holler2021 was invoked but never defined (see the help page).
  3. ^ a b c d e f Cite error: The named reference Brown2023 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference Szakats2022 was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference Grundy-Eris was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference IAUC 8747 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Brown2018 was invoked but never defined (see the help page).