Hiʻiaka (moon)

Larger moon of Haumea From Wikipedia, the free encyclopedia

Hiʻiaka (moon)

Hiʻiaka is the larger, outer moon of the trans-Neptunian dwarf planet Haumea. It is named after one of the daughters of Haumea, Hiʻiaka, the patron goddess of the Big Island of Hawaii. 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°. Assuming its estimated diameter of over 300 km is accurate, it may be the fourth- or fifth-largest known moon of a Trans-Neptunian object, after Pluto I Charon, Eris I Dysnomia, Orcus I Vanth, and possibly Varda I Ilmarë and Salacia I Actaea.

Quick Facts Discovery, Discovered by ...
Hiʻiaka
Thumb
In this series of photos taken by the Hubble Space Telescope, the brighter object Hiʻiaka is seen orbiting Haumea (center).
Discovery
Discovered byMichael E. Brown,
Chad Trujillo,
David Rabinowitz, et al.
Discovery date26 January 2005
Designations
Designation
Haumea I
(136108) Haumea I Hiʻiaka
Pronunciation/hʔiˈɑːkə/
Hawaiian: [ˈhiʔiˈjɐkə]
(136108) 2003 EL61 I
S/2005 (2003 EL61) 1
Orbital characteristics[1]
49880±198 km
Eccentricity0.0513±0.0078
49.12±0.03 d
152.8°±6.1°
Inclination126.356±0.064°
206.766°±0.033°
154.1°±5.8°
Satellite ofHaumea
Physical characteristics
Dimensions(476±88) × (370±52) × (286±14) km[2]:162
369±23 km[2]:162
Mass(1.79±0.11)×1019 kg[1] (0.45% of Haumea)
Mean density
0.685±0.134 g/cm3[2]:163
9.68±0.03 h[2]:160
~9.8 h[3]
Albedo0.68±0.05[2]:162
Temperature32±3 K
20.3 (3.0 difference from primary's 17.3)[4]
3.24±0.08[2]:163
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    Discovery

    Hiʻiaka was the first satellite discovered around Haumea. It was discovered on 26 January 2005 and nicknamed "Rudolph" by the discovery team before being assigned an official name.[citation needed]

    Physical characteristics

    Summarize
    Perspective

    Size and brightness

    Stellar occultations by Hiʻiaka on 6 and 16 April 2021 reveal that the moon is elongated, with estimated ellipsoid dimensions of 476 km × 370 km × 286 km (296 mi × 230 mi × 178 mi).[2]:162 These correspond to a volume-equivalent diameter of 369 km (229 mi).[2]:162 To put this in perspective, if Hiʻiaka were in the asteroid belt, it would be larger than all but the four largest asteroids, after 1 Ceres, 2 Pallas, 4 Vesta, and 10 Hygiea. In spite of its relatively large size, Hiʻiaka is not in hydrostatic equilibrium because its elongated shape is inconsistent with that expected for its current rotation period.[2]:164

    Mass and density

    The mass of Hiʻiaka is estimated to be (1.79±0.11)×1019 kg using precise relative astrometry from the Hubble Space Telescope and Keck Telescope and applying 3-body, point-mass model to the Haumean system.[1] Hiʻiaka's diameter and mass indicate it has a low density of 0.685 g/cm3, which suggests Hiʻiaka's interior consists of highly porous water ice with a rock mass fraction between 50% and 70%.[2]:163–164

    Spectrum and composition

    The near infrared spectrum of Hiʻiaka is dominated by water-ice absorption bands, which means that its surface is made mainly of water ice. The presence of the band centered at 1.65 μm indicates that the surface water 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.[5]

    See also

    References

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