Dysnomia (moon)

Dysnomia
	Low-resolution image of Eris and Dysnomia as imaged by the Hubble Space Telescope, August 2006
Discovery
Discovered by	Brown et al.
Discovery date	10 September 2005
Designations
Designation	Eris I
Pronunciation	/dɪsˈnoʊmiə/, /daɪˈsnoʊmiə/
Named after	Δυσνομία Dysnomia
Alternative names	S/2005 (2003 UB313) 1; Dy /ˈdaɪ/ (nickname); Gabrielle (nickname)
Adjectives	Dysnomian
Orbital characteristics
	Epoch 31 August 2006 (JD 2453979.0)
Semi-major axis	37273±64 km
Eccentricity	0.0062±0.0010
Orbital period (sidereal)	15.785899±0.000050 d
Average orbital speed	0.172 km/s
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)
Longitude of ascending node	126.17°±0.26°
Argument of periapsis	180.83°
Satellite of	Eris
Physical characteristics
Mean diameter	615+60; −50 km
Mass	(8.2±5.7)×1019 kg
Mean density	0.7±0.5 g/cm3
Synodic rotation period	synchronous
Axial tilt	≈ 0° to orbit (assumed)
Albedo	0.05±0.01
Apparent magnitude	25.4
Absolute magnitude (H)	5.6

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

[Brown2006-discovery-2] Cite error: The named reference Brown2006-discovery was invoked but never defined (see the help page).

[Holler2021-4] Cite error: The named reference Holler2021 was invoked but never defined (see the help page).

[Brown2023-8] ^ ^a ^b ^c ^d ^e ^f Cite error: The named reference Brown2023 was invoked but never defined (see the help page).

[Szakats2022-9] Cite error: The named reference Szakats2022 was invoked but never defined (see the help page).

[Grundy-Eris-10] Cite error: The named reference Grundy-Eris was invoked but never defined (see the help page).

[IAUC_8747-12] Cite error: The named reference IAUC 8747 was invoked but never defined (see the help page).

[Brown2018-13] Cite error: The named reference Brown2018 was invoked but never defined (see the help page).

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Discovery
Low-resolution image of Eris and Dysnomia as imaged by the Hubble Space Telescope, August 2006
Discovered by	Brown et al.^[a]^[1]
Discovery date	10 September 2005^[1]
Designations
Designation	Eris I
Pronunciation	/dɪsˈnoʊmiə/, /daɪˈsnoʊmiə/^[b]
Named after	Δυσνομία Dysnomia
Alternative names	S/2005 (2003 UB₃₁₃) 1 Dy /ˈdaɪ/ (nickname) Gabrielle (nickname)
Adjectives	Dysnomian
Orbital characteristics^[2]^: 5
Epoch 31 August 2006 (JD 2453979.0)
Semi-major axis	37273±64 km
Eccentricity	0.0062±0.0010
Orbital period (sidereal)	15.785899±0.000050 d
Average orbital speed	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]
Longitude of ascending node	126.17°±0.26°
Argument of periapsis	180.83°^[e]
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
Synodic rotation period	synchronous^[4]
Axial tilt	≈ 0° to orbit (assumed)
Albedo	0.05±0.01^[3]^: 7
Apparent magnitude	25.4^[f]
Absolute magnitude (H)	5.6^[f]