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Dwarf planets are Ceres, Eris, Haumea, Makemake and Pluto; probable dwarf planets are (225088) 2007 OR10, Sedna, Quaoar, (55565) 2002 AW197, Orcus and 2012 VP113.
Keck image of Haumea and its two moons. Hiʻiaka is above Haumea (centre), and Nāmaka is directly below
Haumea, formal designation 136108 Haumea, is a dwarf planet located beyond Neptune’s orbit. Just one-third the mass of Pluto, it was discovered in 2004 by a team headed by Mike Brown of Caltech at the Palomar Observatory in the United States and, in 2005, by a team headed by J L Ortiz at the Sierra Nevada Observatory in Spain, though the latter claim has been contested and neither is official. On 17th September 2008, it was designated a dwarf planet by the International Astronomical Union (IAU) and named after “Haumea”, the Hawaiian goddess of childbirth.
Haumea’s extreme elongation makes it unique among known dwarf planets. Although its shape has not been directly observed, calculations from its light curve suggest it is an ellipsoid, with its major axis twice as long as its minor. Nonetheless, its gravity is believed sufficient for it to have relaxed into hydrostatic equilibrium, thereby meeting the definition of a dwarf planet. This elongation, along with its unusually rapid rotation, high density, and high albedo (from a surface of crystalline water ice), are thought to be the results of a giant collision, which left Haumea – the largest member of a collisional family that includes several large trans-Neptunian objects (TNOs) – and its two known moons (Hiʻiaka and Nāmaka).
Haumea is a plutoid, a term used to describe dwarf planets beyond Neptune’s orbit. Its status as a dwarf planet means it is presumed to be massive enough to have been rounded by its own gravity but not to have cleared its neighbourhood of similar objects. Although Haumea appears to be far from spherical, its ellipsoidal shape is thought to result from its rapid rotation, in much the same way that a water balloon stretches out when tossed with a spin, and not from a lack of sufficient gravity to overcome the compressive strength of its material. Haumea was initially listed as a classical Kuiper belt object (classical KBO) in 2006 by the Minor Planet Center, but no longer. The nominal trajectory suggests that it is in a fifth-order 7:12 resonance with Neptune since the perihelion distance of 35 AU is near the limit of stability with Neptune. There are precovery images of Haumea dating back to 22nd March 1955 from the Palomar Mountain Digitized Sky Survey. Further observations of the orbit will be required to verify its dynamic status.
The motion of Haumea in a rotating frame with a period equal to Neptune’s orbital period (Neptune is held stationary). It shows the nominal orbit of Haumea librating in a 12:7 resonance to Neptune. Neptune is the blue (stationary) dot at 5 o’clock. Uranus is green, Saturn yellow, and Jupiter pink. Where red turns to green is where it crosses the ecliptic. Notice that these nodes control the reversal. See also 2 Pallas [below] for an example of non-libration.
The diagram illustrates Pallas’s near-18:7 resonance pattern with Jupiter. The motion of Pallas is shown in a reference frame that rotates about the Sun (the centre dot) with a period equal to Jupiter’s orbital period. Accordingly, Jupiter’s orbit appears almost stationary as the pink ellipse at top left. Mars’s motion is orange, and the Earth – Moon system is blue and white. The orbit of Pallas is green when above the ecliptic, and red when below. The near-18:7 resonance pattern with Jupiter only marches clockwise: it never halts or reverses course (so there is no libration)
Haumea was listed as a cubewano (which is pronounced /ˌkju:bi:ˈwʌnoʊ/ or “QB1-o”), a “classical” low-eccentricity KBO that orbits beyond Neptune and is not controlled by an orbital resonance with Neptune. Cubewanos have orbits with semi-major axes in the 40 to 50 AU range and, unlike Pluto, do not cross Neptune’s orbit; that is, they have low-eccentricity and sometimes low-inclination orbits like the classical planets.
Two teams claim credit for the discovery of Haumea. Mike Brown and his team at Caltech discovered Haumea in December 2004 on images they had taken on 6th May 2004. On 20th July 2005, they published an online abstract of a report intended to announce the discovery at a conference in September 2005. At around this time, José Luis Ortiz Moreno and his team at the Instituto de Astrofísica de Andalucía at Sierra Nevada Observatory in Spain found Haumea on images taken on 7th to 10th March 2003. Ortiz emailed the Minor Planet Center with their discovery on the night of 27th July 2005.
Brown initially conceded discovery credit to Ortiz, but came to suspect the Spanish team of fraud upon learning that his observation logs were accessed from the Spanish observatory the day before the discovery announcement. These logs included enough information to allow the Ortiz team to precover Haumea in their 2003 images, and they were accessed again just before Ortiz’s scheduled telescope time to obtain confirmation images for a second announcement to the MPC on 29th July. Ortiz later admitted he had accessed the Caltech observation logs but denied any wrongdoing, stating he was merely verifying whether they had discovered a new object.
IAU protocol is that discovery credit for a minor planet goes to whoever first submits a report to the Minor Planet Center with enough positional data for a decent determination of its orbit, and that the credited discoverer has priority in choosing a name. However, the IAU announcement on 17th September 2008, that Haumea had been accepted as a dwarf planet, did not mention a discoverer. The location of discovery was listed as the Sierra Nevada Observatory of the Spanish team, but the chosen name, Haumea, was the Caltech proposal; Ortiz’s team had proposed Ataecina, named after the ancient Iberian goddess of Spring.
The Spanish team proposed a separate discovery to the MPC in July 2005. On 29th July 2005, Haumea was given its first official label, the temporary designation 2003 EL61, with the “2003” based on the date of the Spanish discovery image. On 7th September 2006, it was numbered and admitted into the official minor planet catalogue as (136108) 2003 EL61.
Following guidelines established by the IAU that classical KBOs be given names of mythological beings associated with creation, in September 2006 the Caltech team submitted formal names from Hawaiian mythology to the IAU for both (136108) 2003 EL61 and its moons, in order “to pay homage to the place where the satellites were discovered”. The names were proposed by David Rabinowitz of the Caltech team. Haumea is the matron goddess of the island of Hawaiʻi, where the Mauna Kea Observatory is located. In addition, she is identified with Pāpā, the goddess of the earth and wife of Wākea (space), which is appropriate because 2003 EL61 is thought to be composed almost entirely of solid rock, without the thick ice mantle over a small rocky core typical of other known Kuiper belt objects. Lastly, Haumea is the goddess of fertility and childbirth, with many children who sprang from different parts of her body; this corresponds to the swarm of icy bodies thought to have broken off the dwarf planet during an ancient collision. The two known moons, also believed to have formed in this manner, are thus named after two of Haumea’s daughters, Hiʻiaka and Nāmaka.
Orbits of Haumea (yellow) and Pluto (red), relative to that of Neptune (grey), as of May 2009
Haumea has a typical orbit for a classical Kuiper-belt object, with an orbital period of 283 Earth years, a perihelion of 35 AU, and an orbital inclination of 28°. It passed aphelion in early 1992, and is currently more than 50 AU from the Sun.
Haumea’s orbit has a slightly greater eccentricity than the other members of its collisional family. This is thought to be due to Haumea’s weak fifth-order 12:7 orbital resonance with Neptune gradually modifying its initial orbit over the course of a billion years, through the Kozai effect, which allows the exchange of an orbit’s inclination for increased eccentricity.
With a visual magnitude of 17.3, Haumea is the third-brightest object in the Kuiper belt after Pluto and Makemake, and easily observable with a large amateur telescope. However, since the planets and most small Solar System bodies share a common orbital alignment from their formation in the primordial disk of the Solar System, most early surveys for distant objects focused on the projection on the sky of this common plane, called the ecliptic. As the region of sky close to the ecliptic became well explored, later sky surveys began looking for objects that had been dynamically excited into orbits with higher inclinations, as well as more distant objects, with slower mean motions across the sky. These surveys eventually covered the location of Haumea, with its high orbital inclination and current position far from the ecliptic.
Its pronunciation is either /haʊˈmeɪ:ə/ (with three syllables according to the English pronunciation in Hawaii) or /hɑ:u:ˈmeɪ:ə/ (with four syllables according to Brown’s students)
Haumea’s orbit has a semi-major axis of 43.132 AU (6.452 Tm), with an eccentricity of 0.19501; its orbital period is 283.28 years (103,468 days) with an average orbital speed of 4.484 km/s and an inclination of 28.22°.
Haumea displays large fluctuations in brightness over a period of 3.9155±0.0001 hours (0.163146±0.000004 day), which can only be explained by a rotational period of this length. This is faster than any other known equilibrium body in the Solar System, and indeed faster than any other known body larger than 100 km in diameter. This rapid rotation is thought to have been caused by the impact that created its satellites and collisional family.
Since Haumea has moons, the mass of the system can be calculated from their orbits using Kepler’s third law. The result is 4.2×1021 kg, 28% the mass of the Plutonian system and 6% the mass of the Earth’s Moon. Nearly all of this mass is in Haumea. Its dimensions are given as ∼1,960×1,518×996 km (Keck), mean radius ∼718 km, 575+125−50 km (Spitzer), and ∼650 km (Herschel). Its surface area is ∼2×107 km2, its mass is (4.006±0.040)×1021 kg (0.00066 of Earth’s), giving a mean density of 2.6 to 3.3 g/cm3. The equatorial surface gravity is 0.44 m/s2 and the escape velocity is 0.84 km/s.
Haumea’s albedo is 0.7±0.1 (according to D L Rabinowitz et al. (2006)), 0.84+0.1−0.2 (J Stansberry, W Grundy, M Brown, et al. (2008)), 0.70 to 0.75 (E Lollouch et al. (2010)), and its temperature is less than 50 K. Its apparent magnitude is 17.3 at opposition, with an absolute magnitude of 0.0336±0.43.
The calculated ellipsoid shape of Haumea, 1,960×1,518×996 km (assuming an albedo of 0.73). At left are the minimum and maximum equatorial silhouettes (1,960×996 and 1,518×996 km); at right is the view from the pole (1,960×1,518 km)
The size of a Solar System object can be deduced from its optical magnitude, its distance, and its albedo. Objects appear bright to Earth observers either because they are large or because they are highly reflective. If their reflectivity (albedo) can be ascertained, then a rough estimate can be made of their size. For most distant objects, the albedo is unknown, but Haumea is large and bright enough for its thermal emission to be measured, which has given an approximate value for its albedo and thus its size. However, the calculation of its dimensions is complicated by its rapid rotation. The rotational physics of deformable bodies predicts that over as little as a hundred days, a body rotating as rapidly as Haumea will have been distorted into the equilibrium form of a scalene ellipsoid. It is thought that most of the fluctuation in Haumea’s brightness is caused not by local differences in albedo but by the alternation of the side view and end view as seen from Earth.
The rotation and amplitude of Haumea’s light curve place strong constraints on its composition. If Haumea had a low density like Pluto, with a thick mantle of ice over a small rocky core, its rapid rotation would have elongated it to a greater extent than the fluctuations in its brightness allow. Such considerations constrain its density to a range of 2.6 to 3.3 g/cm3. This range covers the values for silicate minerals such as olivine and pyroxene, which make up many of the rocky objects in the Solar System. This suggests that the bulk of Haumea is rock covered with a relatively thin layer of ice. A thick ice mantle more typical of Kuiper belt objects may have been blasted off during the impact that formed the Haumean collisional family.
The denser the object in hydrostatic equilibrium, the more spherical it must be for a given rotational period, placing constraints on Haumea’s possible dimensions. Fitting its accurately known mass, its rotation, and its inferred density to an equilibrium ellipsoid predicts that Haumea is approximately the diameter of Pluto along its longest axis and about half that at its poles. Since no observations of occultations of stars by Haumea or occultations of the dwarf planet with its moons have yet been made, direct, precise measurements of its dimensions, like those that have been made for Pluto, do not yet exist.
Several ellipsoid-model calculations of Haumea’s dimensions have been made. The first model produced after Haumea’s discovery was calculated from ground-based observations of Haumea’s light curve at optical wavelengths: it provided a total length of 1,960 to 2,500 km and a visual albedo greater than 0.6. The most likely shape is a triaxial ellipsoid. Subsequent light-curve analyses have suggested an equivalent circular diameter of 1,450 km. In 2010 an analysis of measurements taken by Herschel Space Telescope together with the older Spitzer Telescope measurements yielded a new estimate of the equivalent diameter of Haumea – about 1300 km. These independent size estimates overlap at an average geometric mean diameter of roughly 1,400 km. This makes Haumea one of the largest trans-Neptunian objects discovered, smaller than Eris, Pluto, probably Makemake, and possibly 2007 OR10, and larger than Sedna, Quaoar, and Orcus.
In 2005, the Gemini and Keck telescopes obtained spectra of Haumea which showed strong crystalline water ice features similar to the surface of Pluto’s moon Charon. This is peculiar, because crystalline ice forms at temperatures above 110 K, while the surface temperature of Haumea is below 50 K, a temperature at which amorphous ice is formed. In addition, the structure of crystalline ice is unstable under the constant rain of cosmic rays and energetic particles from the Sun that strike trans-Neptunian objects. The timescale for the crystalline ice to revert to amorphous ice under this bombardment is of the order of ten million years, while trans-Neptunian objects have been in their present cold-temperature locations for timescales of thousands of millions of years. Radiation damage should also redden and darken the surface of trans-Neptunian objects where the common surface materials of organic ices and tholin-like compounds are present, as is the case with Pluto. Therefore, the spectra and colour suggest Haumea and its family members have undergone recent resurfacing that produced fresh ice. However, no plausible resurfacing mechanism has been suggested.
Haumea is as bright as snow, with an albedo in the range of 0.6 to 0.8, consistent with crystalline ice. Other large TNOs such as Eris appear to have albedos as high or higher. Best-fit modelling of the surface spectra suggested that 66% to 80% of the Haumean surface appears to be pure crystalline water ice, with one contributor to the high albedo possibly hydrogen cyanide or phyllosilicate clays. Inorganic cyanide salts such as copper potassium cyanide may also be present.
However, further studies of the visible and near infrared spectra suggest a homomorphous surface covered by an intimate 1:1 mixture of amorphous and crystalline ice, together with no more than 8% organics. The absence of ammonia hydrate excludes cryovolcanism and the observations confirm that the collisional event must have happened more than 100 million years ago, in agreement with the dynamic studies. The absence of measurable methane in the spectra of Haumea is consistent with a warm collisional history that would have removed such volatiles, in contrast to Makemake.
In addition to the large fluctuations in Haumea’s light curve due to the body’s shape, which affect all colours equally, smaller independent colour variations seen in both visible and near-infrared wavelengths show a region on the surface that differs both in colour and in albedo. More specifically, a large dark red area on Haumea’s bright white surface was seen in September 2009, possibly an impact feature, which indicates an area rich in minerals and organic (carbon-rich) compounds, or possibly a higher proportion of crystalline ice. Thus Haumea may have a mottled surface reminiscent of Pluto, if not as extreme.
Artist’s depiction of Haumea with its moons Hiʻiaka and Nāmaka. The moons are much more distant than suggested here
Two small satellites have been discovered orbiting Haumea (sometimes called a trinary system), (136108) Haumea I Hiʻiaka and (136108) Haumea II Nāmaka. Brown’s team discovered both in 2005, through observations of Haumea using the W M Keck Observatory.
Hiʻiaka was discovered on 26th January 2005. It is the outer and, at roughly 310 km in diameter, the larger and brighter of the two, and orbits Haumea in a nearly circular path every 49 days. Strong absorption features at 1.5 and 2 micrometres in the infrared spectrum are consistent with nearly pure crystalline water ice covering much of the surface. The unusual spectrum, along with similar absorption lines on Haumea, led Brown and colleagues to conclude that capture was an unlikely model for the system’s formation, and that the Haumean moons must be fragments of Haumea itself.
Nāmaka, the smaller, inner satellite of Haumea, was discovered on 30th June 2005. It is a tenth the mass of Hiʻiaka, orbits Haumea in 18 days in a highly elliptical, non-Keplerian orbit, and as of 2008 is inclined 13° from the larger moon, which perturbs its orbit. The relatively large eccentricities together with the mutual inclination of the orbits of the satellites are unexpected as they should have been damped by the tidal effects. A relatively recent passage by a 3:1 resonance might explain the current excited orbits of the Haumean moons.
At present, the orbits of the Haumean moons appear almost exactly edge-on from Earth, with Nāmaka periodically occulting 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 with Pluto and Charon. The tiny change in brightness of the system during these occultations will require at least a medium-aperture professional telescope for detection. Hiʻiaka 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 satellites, Nāmaka’s orbit is being greatly torqued by Hiʻiaka, preserving the viewing angle of Nāmaka–Haumea transits for several more years.
Haumea is the largest member of its collisional family, a group of astronomical objects with similar physical and orbital characteristics thought to have formed when a larger progenitor was shattered by an impact. This family is the first to be identified among TNOs and includes – beside Haumea and its moons – (55636) 2002 TX300 (∼364 km), (24835) 1995 SM55 (∼174 km), (19308) 1996 TO66 (∼200 km), (120178) 2003 OP32 (∼230 km) and (145453) 2005 RR43 (∼252 km). Brown et al. proposed that the family were a direct product of the impact that removed Haumea’s ice mantle, but a second proposal suggests a more complicated origin: that the material ejected in the initial collision instead coalesced into a large moon of Haumea, which was later shattered in a second collision, dispersing its shards outwards. This second scenario appears to produce a dispersion of velocities for the fragments that is more closely matched to the measured velocity dispersion of the family members.
The presence of the collisional family could imply that Haumea and its “offspring” might have originated in the scattered disc. In today’s sparsely populated Kuiper belt, the chance of such a collision occurring over the age of the Solar System is less than 0.1 percent. The family could not have formed in the denser primordial Kuiper belt because such a close-knit group would have been disrupted by Neptune’s migration into the belt—the believed cause of the belt’s current low density. Therefore it appears likely that the dynamic scattered disc region, in which the possibility of such a collision is far higher, is the place of origin for the object that generated Haumea and its kin.
Because it would have taken at least a billion years for the group to have diffused as far as it has, the collision which created the Haumea family is believed to have occurred very early in the Solar System’s history.
Haumea’s moons are unusual in a number of ways. They are thought to be part of its extended collisional family, which formed billions of years ago from icy debris after a large impact disrupted Haumea’s ice mantle. Hiʻiaka, the larger, outermost moon, has large amounts of pure water ice on its surface, a feature rare among Kuiper belt objects. Nāmaka, about one tenth the mass, has an orbit with surprising dynamics: it is unusually eccentric and appears to be greatly influenced by the larger satellite.
Two small satellites 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 and larger of the two satellites was discovered on 26th January 2005, and formally designated S/2005 (2003 EL61) 1. The smaller, inner satellite of Haumea was discovered on 30th June 2005, formally termed S/2005 (2003 EL61) 2. On 7th September 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 on 17th September 2008: (136108) Haumea I Hiʻiaka and (136108) Haumea II Nāmaka. Each moon was named after a daughter of Haumea, the Hawaiian goddess of fertility and childbirth. Hiʻiaka is the goddess of dance and patroness of the Big Island of Hawaii, where the Mauna Kea Observatory is located. Nāmaka 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 objects in Haumea’s collisional family. There could therefore be additional outer moons, smaller than Nāmaka, that have not yet been detected. However, HST 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’s gravitational influence (its Hill sphere). This makes it unlikely that any more exist.
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 micrometres in its infrared 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 as Haumea, which is reasonable as their spectra show them to have the same surface composition. Haumea’s albedo has been measured by the Spitzer Space Telescope: 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, Nāmaka, which is a tenth the mass of Hiʻiaka, would be about 170 km in diameter.
The 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 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’s spectrum.
The moons of Haumea are too faint to detect with telescopes smaller than about 2 metres in aperture, though Haumea itself has a visual magnitude of 17.5, making it the third brightest object in the Kuiper belt after Pluto and Makemake, and easily observable with a large amateur telescope.
The orbits of Hiʻiaka (blue) and Nāmaka (green)
Hiʻiaka orbits Haumea in a nearly circular path every 49 days. Nāmaka orbits Haumea in 18 days in a highly elliptical, non-Keplerian orbit, and as of 2008 is inclined 13° from the larger moon, which perturbs 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 into a more circular orbit. Current research suggests that Nāmaka’s orbit has been disturbed by orbital resonances with the more massive Hiʻiaka, due to converging orbits as the two moons move outward from Haumea due to tidal dissipation. 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. This resonance strongly perturbs Nāmaka’s orbit, which has a current precession of the argument of periapsis by about −6.5° per year, implying a precession period of 55 years.
At present, the orbits of the Haumean moons appear almost exactly edge-on from Earth, with Nāmaka periodically occulting 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 with Pluto and Charon. The tiny change in brightness of the system during these occultations will require at least a medium-aperture professional telescope for detection. Hiʻiaka 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 satellites, the great torquing of Nāmaka’s orbit by Hiʻiaka will preserve the viewing angle of Nāmaka–Haumea transits for several more years.
Hiʻiaka was the first satellite discovered around 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 49.462±0.083 days at a distance (semi-major axis) of 49,880±198 km, with an eccentricity of 0.0513±0.0078 and an inclination of 126.356±0.064°. Mutual events expected in July 2009 should improve the knowledge of the orbits and masses of the components of the Haumean system. It is pronounced /hiːʔiːˈɑːkə/; the Hawaiian pronunciation is /ˈhiʔiˈjɐkə/.
Hiʻiaka is the larger, outer moon of the dwarf planet Haumea. Its measured brightness is 5.9±0.5%, translating into a diameter of about 22% of its primary, or of the order of 350 km, assuming a similar albedo. To put this in perspective, this would make it larger than all but four of the asteroids, after 1 Ceres, 2 Pallas, 4 Vesta, and 10 Hygiea. Future exploration of Haumea and its moons could reveal that Hiʻiaka is in hydrostatic equilibrium, i.e. rounded by its own gravity. However, it is not a dwarf-planet candidate because it is a moon. The mass of Hiʻiaka is estimated to be 1.79±0.11×1019 kg (about 0.45% of that of Haumea) using precise relative astrometry from the Hubble and Keck telescopes and applying 3-body, point-mass model to the Haumean system. Its mean density is about 1 g/cm3, and its temperature is 32±3 K.
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 1.65 μm 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 rays. Hiʻiaka’s apparent magnitude is 3.3 different from the primary’s 17.3.
Nāmaka 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. It was discovered on 30th June 2005 and announced on 29th November 2005. It orbits the primary in 18.2783±0.0076 days, the orbit having a semi-major axis of 25,657±91 km, an eccentricity of 0.249±0.015 (in 2009, variable), and an inclination of 113.013±0.075° (13.41±0.08° relative to Hiʻiaka (in 2008, variable)).
Nāmaka is only 1.5% as bright as its dwarf planet Haumea and is about 0.05% its mass (about 1.79±1.48×1018 kg). If it turns out to have a similar albedo to the primary’s 0.7±0.1, it would be about 170 km in diameter. Photometric observations indicate that its surface is made of water ice. Its mean density is assumed to be near 1, and its temperature is 32±3 K. Nāmaka’s apparent magnitude is 4.6 different from the primary’s 17.3. It is pronounced /nɑːˈmɑːkə/; the Hawaiian pronunciation is /naːˈmɐkə/.