Hiiaka is the larger, outer moon of the trans-Neptunian

dwarf planet A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to ...

Haumea , discoverer = , discovered = , earliest_precovery_date = March 22, 1955 , mpc_name = (136108) Haumea , pronounced = , adjectives = Haumean , note = yes , alt_names = , named_after = Haumea , mp_category = , orbit_ref = , epoc ...

. It is named after one of the daughters of

, Hiiaka, the patron goddess of the

Big Island of Hawaii Hawaii ( ; haw, Hawaii ) is the largest island in the United States, located in the state of Hawaii. It is the southeasternmost of the Hawaiian Islands, a chain of volcanic islands in the North Pacific Ocean. With an area of , it has 63% of t ...

. It orbits once every at a distance of , with an eccentricity of and an inclination of . 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 Dysnomia (formally (136199) Eris I Dysnomia) is the only known moon of the dwarf planet Eris and is likely the second-largest known moon of a dwarf planet, after Pluto I Charon. It was discovered in September 2005 by Mike Brown and the Laser ...

, Orcus I Vanth, and possibly Varda I Ilmarë and Salacia I Actaea.

Discovery

Hiiaka was the first

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...

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 , translating into a diameter of about 22% of its primary, or in the range of , assuming similar infrared albedo. To put this in perspective, if Hi'iaka were in the asteroid belt, it would be larger than all but the

four 4 (four) is a number, numeral and digit. It is the natural number following 3 and preceding 5. It is the smallest semiprime and composite number, and is considered unlucky in many East Asian cultures. In mathematics Four is the smallest ...

largest asteroids, after

1 Ceres Ceres (; minor-planet designation: 1 Ceres) is a dwarf planet in the asteroid belt between the orbits of Mars and Jupiter. It was the first asteroid discovered, on 1 January 1801, by Giuseppe Piazzi at Palermo Astronomical Observatory in Sici ...

2 Pallas Pallas ( minor-planet designation: 2 Pallas) is the second asteroid to have been discovered, after Ceres. It is believed to have a mineral composition similar to carbonaceous chondrite meteorites, like Ceres, though significantly less hy ...

4 Vesta Vesta ( minor-planet designation: 4 Vesta) is one of the largest objects in the asteroid belt, with a mean diameter of . It was discovered by the German astronomer Heinrich Wilhelm Matthias Olbers on 29 March 1807 and is named after Vesta, t ...

, and

10 Hygiea Hygiea ( minor-planet designation: 10 Hygiea) is a major asteroid and possible dwarf planet located in the main asteroid belt. With a diameter of and a mass estimated to be 3% of the total mass of the belt, it is the fourth-largest asteroid i ...

. 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.

Mass

The mass of Hiiaka is estimated to be using precise relative

astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. Hist ...

from the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

and

Keck Telescope The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when co ...

and applying 3-body, point-mass model to the Haumean system.

Spectrum and composition

The near infrared spectrum of Hiiaka 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 indicates that the surface water ice is primarily in the

crystalline A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

form. Currently it is unclear why water ice on the surface has not turned into

amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek language, Gr ...

form as would be expected due to its constant irradiation by

cosmic ray Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...

Notes

References

External links

Brown's publication describing the discovery of Hiiaka

Paper describing the composition of Hiiaka
{{DEFAULTSORT:Hi'iaka (moon) Moons of Haumea Trans-Neptunian satellites Discoveries by Michael E. Brown Discoveries by Chad Trujillo Discoveries by David L. Rabinowitz Objects observed by stellar occultation