Hiʻiaka (moon)

Hiʻiaka

In this series of photos taken by the Hubble Space Telescope, the brighter object Hiʻiaka is seen orbiting Haumea (center).
Discovery
Discovered by	Michael E. Brown, Chad Trujillo, David Rabinowitz, et al.
Discovery date	26 January 2005
Designations
Designation	Haumea I
Pronunciation	/hiːʔiˈɑːkə/ Hawaiian: [ˈhiʔiˈjɐkə]
Alternative names	(136108) 2003 EL61 I S/2005 (2003 EL61) 1
Orbital characteristics[1]
Semi-major axis	49880±198 km
Eccentricity	0.0513±0.0078
Orbital period (sidereal)	49.12±0.03 d
Mean anomaly	152.8°±6.1°
Inclination	126.356±0.064°
Longitude of ascending node	206.766°±0.033°
Argument of perihelion	154.1°±5.8°
Satellite of	Haumea
Physical characteristics
Mean radius	~160 km[1]
Mass	(1.79±0.11)×1019 kg[1] (0.45% of Haumea)
Mean density	~1 g/cm3
Synodic rotation period	~9.8 h[2]
Albedo	0.8±0.07[3][1]
Temperature	32±3 K
Apparent magnitude	20.3 (3.0 difference from primary's 17.3)[3]

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.

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]}

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 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, however, lightcurve studies suggest that Hiʻiaka is not a gravitationally collapsed spheroid; they further suggest that Hiʻiaka is not tidally locked and has a rotation period of about 9.8 hours.^[2]

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]

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]

• Namaka, the other moon of Haumea

• Brown's publication describing the discovery of Hiʻiaka
• Paper describing the composition of Hiʻiaka