Hiʻiaka (moon)

Hiʻiaka is the larger, outer moon of the possible 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, very possibly Varda I Ilmarë, and perhaps Salacia I Actaea.

Hiʻiaka
Hiʻiaka is above Haumea (center) in this Keck telescope image.
Discovery
Discovered byMichael E. Brown,
Chad Trujillo,
David Rabinowitz, et al.
Discovery date26 January 2005
Designations
Designation
Haumea I
Pronunciation/hiːʔiˈɑːkə/
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
Inclination126.356±0.064°
Satellite ofHaumea
Physical characteristics
Mean radius
~160 km[1]
Mass(1.79±0.11)×1019 kg[1] (0.45% of Haumea)
Mean density
~1 g/cm3
Albedo0.8±0.07[2][1]
Temperature32±3 K
20.3 (3.0 difference from primary's 17.3)[2]

    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.

    Physical characteristics

    Size and brightness

    Its measured brightness is 5.9±0.5%, translating into a diameter of about 22% of its primary, or in the range of 320 km, assuming similar infrared albedo.[1] To put this in perspective, if Hi'iaka 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, however, lightcurve studies suggest that Hi'iaka is not a gravitationally collapsed spheroid; they further suggest that Hi'iaka is not tidally locked and has a rotation period of about 9.8 hours.[3]

    Mass

    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.[1]

    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.[4]

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    See also

    Notes

        References
        1. Ragozzine, D.; Brown, M. E. (2009). "Orbits and Masses of the Satellites of the Dwarf Planet Haumea (2003 EL61)". The Astronomical Journal. 137 (6): 4766–4776. arXiv:0903.4213. Bibcode:2009AJ....137.4766R. doi:10.1088/0004-6256/137/6/4766.CS1 maint: ref=harv (link)
        2. Wm. Robert Johnston (17 September 2008). "(136108) Haumea, Hi'iaka, and Nāmaka". Retrieved 18 September 2008.
        3. Ragozzine, D. (17 October 2016). "Rapidly Rotating Regular Satellites and Tides". www.planetary.org. Retrieved 14 November 2018.
        4. Dumas, C.; Carry, B.; Hestroffer, D.; Merlin, F. (2011). "High-contrast observations of (136108) Haumea". Astronomy & Astrophysics. 528: A105. arXiv:1101.2102. Bibcode:2011A&A...528A.105D. doi:10.1051/0004-6361/201015011.

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