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Hi'iaka (moon)
Encyclopedia
Hiiaka is the larger, outer moon of the dwarf planet
Haumea.
discovered around Haumea. It is named after one of the daughters of Haumea, Hiiaka, 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 at a distance of , with an eccentricity of and an inclination of . Mutual events expected in July 2009 should improve the knowledge of the orbits and masses of the components of the Haumean system.
, 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.
from Hubble Telescope and Keck Telescope and applying 3-body, point-mass model to the Haumean system.
s.
Dwarf planet
A dwarf planet, as defined by the International Astronomical Union , is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite...
Haumea.
Discovery and naming
Hiiaka was the first satelliteNatural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
discovered around Haumea. It is named after one of the daughters of Haumea, Hiiaka, the patron goddess of the Big Island of Hawaii, though at first it had gone by the nickname "Rudolph
Rudolph the Red-Nosed Reindeer
Rudolph the Red-nosed Reindeer is a fictional reindeer with a glowing red nose. He is popularly known as "Santa's 9th Reindeer" and, when depicted, is the lead reindeer pulling Santa's sleigh on Christmas Eve. The luminosity of his nose is so great that it illuminates the team's path through...
" by its discovery team. It orbits once every at a distance of , with an eccentricity of and an inclination of . Mutual events expected in July 2009 should improve the knowledge of the orbits and masses of the components of the Haumean system.
Size and brightness
Its measured brightness is , translating into the diameter about 22% of its primary, or in the range of , assuming similar albedo. To put this in perspective, this moon would be the fifth largest (cis-neptunian) asteroid after 1 Ceres1 Ceres
Ceres, formally 1 Ceres, is the smallest identified dwarf planet in the Solar System and the only one in the asteroid belt. With a diameter of about 950 km, Ceres is by far the largest and most-massive asteroid, comprising about a third of the mass of the asteroid belt. Discovered on 1 January 1801...
, 2 Pallas
2 Pallas
Pallas, formally designated 2 Pallas, is the second asteroid to have been discovered , and one of the largest. It is estimated to constitute 7% of the mass of the asteroid belt, and its diameter of 530–565 km is comparable to, or slightly larger than, that of 4 Vesta. It is however 20%...
, 4 Vesta
4 Vesta
Vesta, formally designated 4 Vesta, is one of the largest asteroids, with a mean diameter of about . It was discovered by Heinrich Wilhelm Olbers on March 29, 1807, and is named after the Roman virgin goddess of home and hearth, Vesta....
, and 10 Hygiea
10 Hygiea
10 Hygiea is an asteroid located in the asteroid belt. With somewhat oblong diameters of 350–500 km, and a mass estimated to be 2.9% of the total mass of the belt, it is the fourth largest asteroid by volume and mass...
if it were in the asteroid belt
Asteroid belt
The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...
. 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
Namaka (moon)
Namaka is the smaller, inner moon of the dwarf planet Haumea. It is named after Nāmaka, one of the daughters of Haumea, the goddess of the sea in Hawaiian mythology.- Discovery :Namaka was discovered on 30 June 2005 and announced on November 29, 2005...
, it is a moon.
Mass
The mass of Hiiaka is estimated to be using precise relative astrometryAstrometry
Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...
from Hubble Telescope and Keck Telescope and applying 3-body, point-mass model to the Haumean system.
Spectrum and composition
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 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 rayCosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
s.