Moons of Haumea - AbsoluteAstronomy.com

The outer Solar System dwarf planet

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 has two known moons
Natural 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....

, Hiiaka

Hi'iaka (moon)

Hiiaka is the larger, outer moon of the dwarf planet Haumea.- Discovery and naming :Hiiaka was the first satellite 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...

and 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...

, named after Hawaiian

Hawaiian mythology

Hawaiian mythology refers to the legends, historical tales and sayings of the ancient Hawaiian people. It is considered a variant of a more general Polynesian mythology, developing its own unique character for several centuries before about 1800. It is associated with the Hawaiian religion...

goddesses. These small moons were discovered in 2005, from observations of Haumea made at the large telescopes of the W. M. Keck Observatory in Hawaii.

Haumea's moons are unusual in a number of ways. They are thought to be part of its extended collisional family

Haumea family

The Haumea family is the only identified trans-Neptunian collisional family; that is, the only group of trans-Neptunian objects with similar orbital parameters and spectra that suggest they originated in the disruptive impact of a progenitor body...

, which formed billions of years ago from icy debris after a large impact disrupted Haumea's ice

Volatiles

In planetary science, volatiles are that group of chemical elements and chemical compounds with low boiling points that are associated with a planet's or moon's crust and/or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, and methane, all compounds of C, H, O...

mantle

Mantle (geology)

The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....

. Hiiaka, the larger, outermost moon, has large amounts of pure water ice on its surface, a feature rare among Kuiper belt

Kuiper belt

The Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...

objects. Namaka, about one tenth the mass, has an orbit with surprising dynamics: it is unusually eccentric

Orbital eccentricity

The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...

and appears to be greatly influenced by the larger satellite.

Discovery and naming

Two small satellites

Natural 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....

were discovered around Haumea (which was at that time still designated 2003 EL₆₁) through observations using the W.M. Keck Observatory by a Caltech team in 2005.
The outer

Hi'iaka (moon)

and larger of the two satellites was discovered January 26, 2005, and formally designated S/2005 (2003 EL₆₁) 1, though nicknamed "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 the Caltech team. The smaller, inner

Namaka (moon)

satellite of Haumea was discovered on June 30, 2005, formally termed S/2005 (2003 EL₆₁) 2, and nicknamed "Blitzen". On September 7, 2006, both satellites were numbered and admitted into the official minor planet catalogue as (136108) 2003 EL61 I and II, respectively.

The permanent names of these moons were announced, together with that of 2003 EL₆₁, by the International Astronomical Union

International Astronomical Union

The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...

on September 17, 2008: (136108) Haumea I Hiʻiaka and (136108) Haumea II Namaka. Each moon was named after a daughter of Haumea, the Hawaiian goddess of fertility and childbirth. Hiiaka is the goddess of dance

Hula

Hula is a dance form accompanied by chant or song . It was developed in the Hawaiian Islands by the Polynesians who originally settled there. The hula dramatizes or portrays the words of the oli or mele in a visual dance form....

and patroness of the Big Island of Hawaii, where the Mauna Kea Observatory

Mauna Kea Observatory

The Observatories at Mauna Kea, , are an independent collection of astronomical research facilities located on the summit of Mauna Kea on the Big Island of Hawai'i, USA. The facilities are located in a special land use zone known as the "Astronomy Precinct," which is located in the Mauna Kea...

is located. Nāmaka

Namaka

In Hawaiian mythology, Nāmaka appears as a sea goddess or a water spirit in the Pele cycle. She is an older sister of Pele-honua-mea. She is the daughter of Ku-waha-ilo and Haumea, whose other children are Pele, the Hiiaka sisters, the Kama brothers, and the bird Halulu...

is the goddess of water and the sea; she cooled her sister Pele's lava as it flowed into the sea, turning it into new land.

In her legend, Haumea's many children came from different parts of her body. The dwarf planet Haumea appears to be almost entirely made of rock, with only a superficial layer of ice; most of the original icy mantle is thought to have been blasted off by the impact that spun Haumea into its current high speed of rotation, where the material formed into the small Kuiper belt

Kuiper belt

objects in Haumea's collisional family

Haumea family

. There could therefore be additional outer moons, smaller than Namaka, that have not yet been detected. However, HST

Hubble Space Telescope

The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

observations have confirmed that no other moons brighter than 0.25% of the brightness of Haumea exist within the closest tenth of the distance (0.1% of the volume) where they could be held by Haumea's gravitational influence (its Hill sphere

Hill sphere

An astronomical body's Hill sphere is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit that lies within the planet's Hill sphere. That moon would, in turn, have a Hill sphere of its own...

). This makes it unlikely that any more exist.

Surface properties

Hiʻiaka is the outer and, at roughly 350 km in diameter, the larger and brighter of the two moons. Strong absorption features observed at 1.5, 1.65 and 2 micrometre

Micrometre

A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...

s in its infrared

Infrared

Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

spectrum are consistent with nearly pure crystalline water ice covering much of its surface.
The unusual spectrum, and its similarity to absorption lines in the spectrum of Haumea, led Brown and colleagues to conclude that it was unlikely that the system of moons was formed by the gravitational capture of passing Kuiper belt objects into orbit around the dwarf planet: instead, the Haumean moons must be fragments of Haumea itself.

The sizes of both moons are calculated with the assumption that they have the same infrared albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

as Haumea, which is reasonable as their spectra show them to have the same surface composition. Albedo has been measured for the dwarf planet by the Spitzer Space Telescope

Spitzer Space Telescope

The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...

: from ground-based telescopes, the moons are too small and close to Haumea to be seen independently. Based on this common albedo, the inner moon, Namaka, which is a tenth the mass of Hiiaka, would be about 170 km in diameter.

The Hubble Space Telescope

Hubble Space Telescope

(HST) has adequate angular resolution to separate the light from the moons from that of Haumea. Photometry of the Haumea triple system with HST's NICMOS camera

Near Infrared Camera and Multi-Object Spectrometer

The Near Infrared Camera and Multi-Object Spectrometer is a scientific instrument for infrared astronomy, installed on the Hubble Space Telescope , operating from 1997 to 1999, and from 2002 to 2008...

has confirmed that the spectral line at 1.6 microns that indicates the presence of water ice is at least as strong in the moons' spectra as in Haumea's spectrum.

The moons of Haumea are too faint to detect with telescopes smaller than about 2 metres in aperture

Aperture

In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...

, though Haumea itself has a visual magnitude of 17.5, making it the third brightest object in the Kuiper belt after Pluto

Pluto

Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...

and Makemake, and easily observable with a large amateur telescope.

Orbital characteristics

Hiiaka orbits Haumea in a nearly circular path every 49 days. Namaka orbits Haumea in 18 days in a highly elliptical, non-Keplerian

Osculating orbit

In astronomy, and in particular in astrodynamics, the osculating orbit of an object in space is the gravitational Kepler orbit In astronomy, and in particular in astrodynamics, the osculating orbit of an object in space (at a given moment of time) is the gravitational Kepler orbit In astronomy,...

orbit, and as of 2008 is inclined 13° from the larger moon, which perturbs

Perturbation (astronomy)

Perturbation is a term used in astronomy in connection with descriptions of the complex motion of a massive body which is subject to appreciable gravitational effects from more than one other massive body....

its orbit. Since the impact that created the moons of Haumea is thought to have occurred in the early history of the Solar System, over the following billions of years it should have been tidally damped

Tidal acceleration

Tidal acceleration is an effect of the tidal forces between an orbiting natural satellite , and the primary planet that it orbits . The "acceleration" is usually negative, as it causes a gradual slowing and recession of a satellite in a prograde orbit away from the primary, and a corresponding...

into a more circular orbit. Current research suggests that Namaka's orbit has been disturbed by orbital resonance

Orbital resonance

In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...

s with the more massive Hiiaka, due to converging orbits as the two moons move outward from Haumea due to tidal dissipation

Tidal acceleration

. The moons may have been caught in and then escaped from orbital resonance several times; they currently are in or at least close to an 8:3 resonance

Orbital resonance

. This resonance strongly perturbs Namaka's orbit, which has a current precession of ~20°.

At present, the orbits of the Haumean moons appear almost exactly edge-on from Earth, with Namaka periodically occulting

Occultation

An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...

Haumea. Observation of such transits would provide precise information on the size and shape of Haumea and its moons, as happened in the late 1980s

Solar eclipses on Pluto

Solar eclipses on Pluto are caused when one of its four natural satellites – Charon, Nix, Hydra, and P4 – passes in front of the Sun, blocking its light....

with Pluto and Charon

Charon (moon)

Charon is the largest satellite of the dwarf planet Pluto. It was discovered in 1978 at the United States Naval Observatory Flagstaff Station. Following the 2005 discovery of two other natural satellites of Pluto , Charon may also be referred to as Pluto I...

. The tiny change in brightness of the system during these occultations will require at least a medium-aperture

Aperture

professional telescope for detection. Hiiaka last occulted Haumea in 1999, a few years before discovery, and will not do so again for some 130 years. However, in a situation unique among regular satellite

Regular moon

In astronomy, a regular moon is a natural satellite following a relatively close and generally prograde orbit with little orbital inclination or eccentricity...

s, the great torquing of Namaka's orbit by Hiiaka will preserve the viewing angle of Namaka–Haumea transits for several more years.

Order Order refers to the position with respect to their average distance from Haumea.	Name (pronunciation) Label refers to the Roman numeral attributed to each moon in order of their discovery.			Mean diameter (km)	Mass (×10²¹ kg)	Semi-major axis (km)	Orbital period (days)	Eccentricity	Inclination (°)	Discovery date
1	Haumea II	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...	/nɑːˈmɑːkə/	~170?	0.00179 ± 0.00148 (~0.05% Haumea)	25657 ± 91	18.2783 ± 0.0076Using Kepler's Law.	0.249 ± 0.015As of 2008: Namaka's eccentricity and inclination are variable Kozai mechanism In celestial mechanics, the Kozai mechanism, or the Lidov-Kozai mechanism, causes a periodic exchange between the inclination and eccentricity of an orbit... due to perturbation.	113.013 ± 0.075 (13.41 ± 0.08° from Hiiaka)	June 2005
2	Haumea I	Hiiaka Hi'iaka (moon) Hiiaka is the larger, outer moon of the dwarf planet Haumea.- Discovery and naming :Hiiaka was the first satellite 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...	/hiːʔiːˈɑːkə/	~310	0.0179 ± 0.0011 (~0.5% Haumea)	49880 ± 198	49.462 ± 0.083	0.0513 ± 0.0078	126.356 ± 0.064°	January 2005

External links

Animation of the orbits of Haumea's moons
International Year of Astronomy 2009
International Year of Astronomy
The International Year of Astronomy was a year-long celebration of astronomy that took place in 2009 to coincide with the 400th anniversary of the first recorded astronomical observations with a telescope by Galileo Galilei and the publication of Johannes Kepler's Astronomia nova in the 17th century...

podcast: Dwarf Planet Haumea (Darin Ragozzine)

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