File:2003 EL61.jpg
Hiʻiaka is above Haumea (center) in this Keck telescope image.
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Discovery | |
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Discovered by | Michael E. Brown, Chad Trujillo, David Rabinowitz, et al. |
Discovery date | 26 January 2005 |
Designations | |
Designation | Haumea I Hiʻiaka |
Pronunciation | /ˌhiːʔiˈɑːkə/,[1] or as in Hawaiian [ˈhiʔiˈjɐkə] |
(136108) 2003 EL61 I, S/2005 (2003 EL61) 1 | |
Orbital characteristics[2] | |
49880±198 km | |
Eccentricity | 0.0513±0.0078 |
49.12±0.03 d | |
Inclination | 126.356±0.064° |
Satellite of | Haumea |
Physical characteristics | |
Mean radius | ~170 km[3] |
Mass | (1.79±0.11)×1019 kg[2](0.45% of Haumea) |
Mean density | ~1 g/cm3 |
(unknown) | |
(unknown) | |
Albedo | (unknown) |
Temperature | 32±3 K |
3.3 difference from primary's 17.3 | |
Hiʻiaka is the larger, outer moon of the dwarf planet Haumea.
Hiʻiaka was the first satellite discovered around Haumea. It is named after one of the daughters of Haumea, Hiʻiaka, the patron goddess of the Big Island of Hawaii, though at first it had gone by the nickname "Rudolph" by its discovery team. It orbits once every 49.12±0.03 d at a distance of 49880±198 km, with an eccentricity of 0.0513±0.0078 and an inclination of 126.356±0.064°. Mutual events expected in July 2009 should improve the knowledge of the orbits and masses of the components of the Haumean system.[2]
Its measured brightness is 5.9±0.5%, translating into the diameter about 22% of its primary, or in the range of 350 km, assuming similar albedo.[2] To put this in perspective, this moon would be the fifth largest (cis-neptunian) asteroid after 1 Ceres, 2 Pallas, 4 Vesta, and 10 Hygiea if it were in the asteroid belt. Future exploration of Haumea and its moons could reveal that Hiʻiaka is rounded by its own gravity, in other words is in hydrostatic equilibrium. However, it would not be a potential dwarf-planet candidate because, like Namaka, it is a moon.
The mass of Hiʻiaka is estimated to be (1.79±0.11)×1019 kg using precise relative astrometry from Hubble Telescope and Keck Telescope and applying 3-body, point-mass model to the Haumean system.[2]
The near infrared spectrum of Hiʻiaka is dominated by water-ice absorption bands, which means that the surface of this moon is made mainly of water ice. The presence of the band centered at 1.65 μm indicates that the ice is primarily in the crystalline form. Currently it is unclear why water ice on the surface has not turned into amorphous form as would be expected due to its constant irradiation by cosmic rays.[3]
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Moons and rings |
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Collisional family |
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Astronomy |
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TNO classes |
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Dwarf planets (moons) |
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Sednoids |
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