Haumea

Haumea (minor-planet designation 136108 Haumea) is a dwarf planet located beyond Neptune's orbit.[25] It was discovered in 2004 by a team headed by Mike Brown of Caltech at the Palomar Observatory in the United States and disputably also in 2005 by a team headed by José Luis Ortiz Moreno at the Sierra Nevada Observatory in Spain, though the latter claim has been contested. On September 17, 2008, it was named after Haumea, the Hawaiian goddess of childbirth, under the expectation by the International Astronomical Union (IAU) that it would prove to be a dwarf planet. Nominal estimates make it the third-largest known trans-Neptunian object, after Eris and Pluto, and approximately the size of Uranus's moon Titania.

136108 Haumea

Hubble image of Haumea (center) and its two moons; Hiʻiaka is above Haumea and Namaka is below
Discovery
Discovered by	Brown et al. Ortiz et al.
Discovery date	December 28, 2004 (Brown) July 27, 2005 (Ortiz)
Designations
MPC designation	(136108) Haumea
Pronunciation	/haʊˈmeɪ.ə, ˌhɑːuː-/[nb 1]
Named after	Haumea
Alternative designations	2003 EL61
Minor planet category	Dwarf planet TNO[4][5] Haumea family trinary[6]
Adjectives	Haumean[7]
Orbital characteristics[8]
Epoch 17 December 2020 (JD 2459200.5)
Uncertainty parameter 2
Observation arc	65 years and 291 days (24033 days)
Earliest precovery date	March 22, 1955
Aphelion	51.585 AU (7.7170 Tm)
Perihelion	34.647 AU (5.1831 Tm)
Semi-major axis	43.116 AU (6.4501 Tm)
Eccentricity	0.19642
Orbital period (sidereal)	283.12 yr (103,410 days)[9]
Average orbital speed	4.53 km/s[nb 2]
Mean anomaly	218.205°
Mean motion	0° 0m 12.533s / day
Inclination	28.2137°
Longitude of ascending node	122.167°
Time of perihelion	≈ 1 June 2133[10] ±2 days
Argument of perihelion	239.041°
Known satellites	2 (Hiʻiaka and Namaka)
Physical characteristics
Dimensions	≈ 2,100 × 1,680 × 1,074 km[nb 3][11] 2,322±60 × 1,704±8 × 1,026±32 km[nb 4][12]
Mean radius	≈ 780 km[nb 3] 798±6 km to 816 km[nb 5]
Surface area	≈ 8.14×106 km2[nb 3][13]
Volume	≈ 1.98×109 km3[nb 3][14] 0.0018 Earths
Mass	(4.006±0.040)×1021 kg[15] 0.00066 Earths
Mean density	≈ 2.018 g/cm3[nb 3] 1.885±0.080 g/cm3 to 1.757 g/cm3[nb 5]
Equatorial surface gravity	0.93 m/s2 at poles to 0.24 m/s2 at longest axis
Equatorial escape velocity	1 km/s at poles to 0.71 km/s at longest axis
Sidereal rotation period	3.915341±0.000005 h[16] (0.163139208 d)
Axial tilt	≈ 126° (to orbit; assumed) 81.2° or 78.9° (to ecliptic)[nb 6]
North pole right ascension	282.6°±1.2°[17]: 3174
North pole declination	−13.0°±1.3° or −11.8°±1.2°[17]: 3174
Geometric albedo	≈ 0.66 geometric[nb 3] ≤ 0.51±0.02 geometric[12] 0.33±0.03 Bond[19]
Temperature	< 50 K[20]
Spectral type	BB (neutral) B−V = 0.64, V−R = 0.33 [21] B0−V0 = 0.646 [22]
Apparent magnitude	17.3 (opposition)[23][24]
Absolute magnitude (H)	0.428±0.011 (V-band) [16] · 0.2 [9]

Haumea's mass is about one-third that of Pluto, and 1/1400 that of Earth. Although its shape has not been directly observed, calculations from its light curve are consistent with it being a Jacobi ellipsoid (the shape it would be if it were a dwarf planet), with its major axis twice as long as its minor. In October 2017, astronomers announced the discovery of a ring system around Haumea, representing the first ring system discovered for a trans-Neptunian object. Haumea's gravity was until recently thought to be sufficient for it to have relaxed into hydrostatic equilibrium, though that is now unclear. Haumea's elongated shape together with its rapid rotation, rings, and high albedo (from a surface of crystalline water ice), are thought to be the consequences of a giant collision, which left Haumea the largest member of a collisional family that includes several large trans-Neptunian objects and Haumea's two known moons, Hiʻiaka and Namaka.