Moons of Haumea

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Animation of Haumea and its moons, imaged by Hubble in 2008. Hi`iaka is the brighter object around Haumea (center), and Namaka is the dimmer object below. Haumea-moons-hubble.gif
Animation of Haumea and its moons, imaged by Hubble in 2008. Hiʻiaka is the brighter object around Haumea (center), and Namaka is the dimmer object below.
Scale diagram of Haumea, the ring, and orbits of its two moons Haumea ring moons diagram.png
Scale diagram of Haumea, the ring, and orbits of its two moons

The outer Solar System planetoid Haumea has two known moons, Hiʻiaka and Namaka , named after Hawaiian 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.

Contents

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, which is rare among Kuiper belt objects. [1] Namaka, 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.

History

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 26 January 2005, [2] and formally designated S/2005 (2003 EL61) 1, though nicknamed "Rudolph" by the Caltech team. [3] The smaller, inner satellite of Haumea was discovered on 30 June 2005, formally termed S/2005 (2003 EL61) 2, and nicknamed "Blitzen". [4] On 7 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 17 September 2008: (136108) Haumea I Hiʻiaka and (136108) Haumea II Namaka. [5] 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. [6] 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. [7]

In her legend, Haumea's many children came from different parts of her body. [7] 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 Namaka, 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 gravitational influence (its Hill sphere). [8] This makes it unlikely that any more exist.

Surface properties

Keck telescope image of Haumea (center), Hi`iaka (above), and Namaka (below). 2003 EL61 Haumea, with moons.jpg
Keck telescope image of Haumea (center), Hiʻiaka (above), and Namaka (below).

Hiʻiaka is the outer and, at roughly 310 km in diameter, the larger and brighter of the two moons. [9] Strong absorption features observed at 1.5, 1.65 and 2 µm 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. [10]

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. [11] Based on this common albedo, the inner moon, Namaka, which is a tenth the mass of Hiʻiaka, would be about 170 km in diameter. [12]

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 µm that indicates the presence of water ice is at least as strong in the moons' spectra as in Haumea's spectrum. [11]

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.

Orbital characteristics

TheKuiperBelt Orbits Haumea moons.svg
A view of the orbits of Hiʻiaka (blue) and Namaka (green)
Haumea mutual events illustration.png
Illustration of mutual events between Haumea and Namaka during 2009–2011

Hiʻiaka orbits Haumea nearly circularly every 49 days. [9] Namaka orbits Haumea in 18 days in a moderately elliptical, non-Keplerian orbit, and as of 2008 was inclined 13° with respect to Hiʻiaka, which perturbs its orbit. [4] Because the impact that created the moons of Haumea is thought to have occurred in the early history of the Solar System, [13] over the following billions of years it should have been tidally damped into a more circular orbit. Namaka's orbit has likely been disturbed by orbital resonances with the more-massive Hiʻiaka due to converging orbits as they moved outward from Haumea due to tidal dissipation. [4] They 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. [4] This resonance strongly perturbs Namaka's orbit, which has a current precession of its argument of periapsis by about −6.5° per year, a precession period of 55 years. [8]

At present, the orbits of the Haumean moons appear almost exactly edge-on from Earth, with Namaka having periodically occulted Haumea from 2009 to 2011. [14] [15] 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. [16] The tiny change in brightness of the system during these occultations required at least a medium-aperture professional telescope for detection. [17] Hiʻiaka last occulted Haumea in 1999, a few years before its discovery, and will not do so again for some 130 years. [18] However, in a situation unique among regular satellites, the great torquing of Namaka's orbit by Hiʻiaka preserved the viewing angle of Namaka–Haumea transits for several more years. [4] [17]

Order
[note 1]
Name
(pronunciation)
[note 2]
Mean diameter
(km)
Mass
(×1018 kg)
Semi-major
axis (km)
Orbital period
(days)
EccentricityInclination (°)Discovery date
0(ring)702285±8 [19] 0.489438±0.000012 [19] [lower-alpha 1] 0January 2017
1Haumea II Namaka /nɑːˈmɑːkə/170?1.79±1.48 [8]
(≈0.05% Haumea)
25657±91 [8] 18.2783±0.0076 [8] [note 3] 0.249±0.015 [8] [note 4] 113.013±0.075 [8]
(13.41±0.08 from Hiʻiaka) [note 4]
June 2005
2Haumea I Hiʻiaka /hiːʔiːˈɑːkə/31017.9±1.1 [8]
(≈0.5% Haumea)
49880±198 [8] 49.462±0.083 [8] [note 3] 0.0513±0.0078 [8] 126.356±0.064 [8] January 2005

Notes

  1. Order refers to the position with respect to their average distance from Haumea.
  2. Label refers to the Roman numeral attributed to each moon in order of their discovery.
  3. 1 2 Using Kepler's third law.
  4. 1 2 As of 2008: Namaka's eccentricity and inclination are variable due to perturbation.
  1. Based on a 3:1 resonance with Haumea's rotation period.

Related Research Articles

Classical Kuiper belt object Kuiper belt object, not controlled by an orbital resonance with Neptune

A classical Kuiper belt object, also called a cubewano ( "QB1-o"), is a low-eccentricity Kuiper belt object (KBO) that orbits beyond Neptune and is not controlled by an orbital resonance with Neptune. Cubewanos have orbits with semi-major axes in the 40–50 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.

Orbital resonance Regular and periodic gravitational influence by two orbiting celestial bodies exerted on each other

In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relationship is found between a pair of objects. The physical principle behind orbital resonance is similar in concept to pushing a child on a swing, whereby the orbit and the swing both have a natural frequency, and the body doing the "pushing" will act in periodic repetition to have a cumulative effect on the motion. Orbital resonances greatly enhance the mutual gravitational influence of the bodies. In most cases, this results in an unstable interaction, in which the bodies exchange momentum and shift orbits until the resonance no longer exists. Under some circumstances, a resonant system can be self-correcting and thus stable. Examples are the 1:2:4 resonance of Jupiter's moons Ganymede, Europa and Io, and the 2:3 resonance between Pluto and Neptune. Unstable resonances with Saturn's inner moons give rise to gaps in the rings of Saturn. The special case of 1:1 resonance between bodies with similar orbital radii causes large solar system bodies to eject most other bodies sharing their orbits; this is part of the much more extensive process of clearing the neighbourhood, an effect that is used in the current definition of a planet.

90482 Orcus Trans-Neptunian object and possible dwarf planet

90482 Orcus, provisional designation 2004 DW, is a trans-Neptunian object with a large moon, Vanth. With a diameter of 910 km (570 mi), it is a possible dwarf planet. The surface of Orcus is relatively bright with albedo reaching 23 percent, neutral in color and rich in water ice. The ice is predominantly in crystalline form, which may be related to past cryovolcanic activity. Other compounds like methane or ammonia may also be present on its surface. It was discovered by American astronomers Michael Brown, Chad Trujillo, and David Rabinowitz on 17 February 2004.

Chad Trujillo American astronomer

Chadwick A. Trujillo is an American astronomer, discoverer of minor planets and the co-discoverer of Eris, the most massive dwarf planet known in the Solar System.

Haumea Dwarf planet in the Solar System

Haumea is a likely dwarf planet located beyond Neptune's orbit. It was discovered in 2004 by a team headed by Mike Brown of Caltech at the Palomar Observatory in the United States and independently in 2005 by a team headed by José Luis Ortiz Moreno at the Sierra Nevada Observatory in Spain, though the latter claim has been contested. On September 17, 2008, it was named after Haumea, the Hawaiian goddess of childbirth, under the expectation by the International Astronomical Union (IAU) that it would prove to be a dwarf planet. Nominal estimates make it the third-largest known trans-Neptunian object, after Eris and Pluto, though the uncertainty in best-fit modeling slightly overlaps with the larger size estimates for Makemake.

Makemake Dwarf planet in the Outer Solar System

Makemake is a likely dwarf planet and perhaps the second-largest Kuiper belt object in the classical population, with a diameter approximately two-thirds that of Pluto. Makemake has one known satellite. Its extremely low average temperature, about 40 K (−230 °C), means its surface is covered with methane, ethane, and possibly nitrogen ices.

<span class="nowrap">(19308) 1996 TO<sub>66</sub></span>

(19308) 1996 TO66 (also written (19308) 1996 TO66) is a trans-Neptunian object that was discovered in 1996 by Chadwick Trujillo, David Jewitt and Jane Luu. Until 20000 Varuna was discovered, it was the second-largest known object in the Kuiper belt, after Pluto.

<span class="nowrap">(55636) 2002 TX<sub>300</sub></span>

(55636) 2002 TX300 is a bright Kuiper belt object in the outer Solar System estimated to be about 286 kilometres (178 mi) in diameter. It is a large member of the Haumea family that was discovered on 15 October 2002 by the Near-Earth Asteroid Tracking (NEAT) program.

Hiʻiaka (moon)

Hiʻiaka is the larger, outer moon of the 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, very possibly Varda I Ilmarë, and perhaps Salacia I Actaea.

Namaka (moon)

Namaka is the smaller, inner moon of the dwarf planet Haumea. It is named after Nāmaka, the goddess of the sea in Hawaiian mythology and one of the daughters of Haumea.

Eris (dwarf planet) Dwarf planet beyond Pluto in the Solar System

Eris is the most massive and second-largest known dwarf planet in the Solar System. Eris is a trans-Neptunian object (TNO), has a high-eccentricity orbit, and is a member of the scattered disk. Eris was discovered in January 2005 by a Palomar Observatory-based team led by Mike Brown, and its discovery was verified later that year. In September 2006 it was named after the Greco-Roman goddess of strife and discord. Eris is the ninth-most massive known object orbiting the Sun, and the sixteenth-most massive overall in the Solar System. It is also the largest object that has not been visited by a spacecraft. Eris has been measured at 2,326 ± 12 kilometers (1,445 ± 7 mi) in diameter. Its mass is 0.27 percent that of the Earth and 127 percent that of dwarf planet Pluto, though Pluto is slightly larger by volume. As Eris orbits the Sun, it completes one rotation every 25.9 hours, making its day length similar to Earth's. However, other sources disagree on the rotation period.

<span class="nowrap">(208996) 2003 AZ<sub>84</sub></span>

(208996) 2003 AZ84 is a trans-Neptunian object with a possible moon from the outer regions of the Solar System. It is approximately 940 kilometers across its longest axis, as it has an elongated shape. It belongs to the plutinos – a group of minor planets named after its largest member Pluto – as it orbits in a 2:3 resonance with Neptune in the Kuiper belt. It was discovered on 13 January 2003, by American astronomers Chad Trujillo and Michael Brown during the NEAT survey using the Samuel Oschin telescope at Palomar Observatory.

(24835) 1995 SM55, provisional designation 1995 SM55, is a trans-Neptunian object and member of the Haumea family that resides in the Kuiper belt, located in the outermost region of the Solar System. It was discovered on 19 September 1995, by American astronomer Nichole Danzl of the Spacewatch program at Kitt Peak National Observatory near Tucson, Arizona, in the United States. It measures approximately 600–700 kilometers in diameter and was the second-brightest known object in the Kuiper belt, after Pluto, until 1996 TO66 was discovered.

<span class="nowrap">(145453) 2005 RR<sub>43</sub></span>

(145453) 2005 RR43, also written as (145453) 2005 RR43, is a trans-Neptunian object (TNO) estimated to be about 250 km in diameter. It was discovered on 9 September 2005 by Andrew Becker, Andrew Puckett and Jeremy Kubica at Apache Point Observatory in Sunspot, New Mexico.

(86047) 1999 OY<sub>3</sub>

(86047) 1999 OY3, also written as (86047) 1999 OY3, is a trans-Neptunian object that resides in the Kuiper belt beyond Pluto. It was discovered on July 18, 1999, at the Mauna Kea Observatory, Hawaii.

<span class="nowrap">(202421) 2005 UQ<sub>513</sub></span>

(202421) 2005 UQ513, also written as 2005 UQ513, is a cubewano with an absolute magnitude of 3.4. Mike Brown's website lists it as a highly likely dwarf planet. (202421) 2005 UQ513's spectrum has a weak signature of absorption by water ice. Like Quaoar, it has a very red spectrum, which indicates that its surface probably contains many complex, processed organic molecules. Its light curve shows variations of Δm=0.3 mag, but no period has been determined.

Haumea family

The Haumea or Haumean family is the only identified trans-Neptunian collisional family; that is, the only group of trans-Neptunian objects (TNOs) with similar orbital parameters and spectra that suggest they originated in the disruptive impact of a progenitor body. Calculations indicate that it is probably the only trans-Neptunian collisional family. Members are known as Haumeids.

Haumea was the first of the IAU-recognized dwarf planets to be discovered since Pluto in 1930. Its naming as a dwarf planet was delayed by several years due to controversy over who should receive credit for its discovery. A California Institute of Technology (Caltech) team headed by Michael E. Brown first noticed the object, but a Spanish team headed by José Luis Ortiz Moreno were the first to announce it, and so normally would receive credit. Brown accused the Spanish team of fraud, using Caltech observations without credit to make their discovery, while the Ortiz team accused the American team of political interference with the International Astronomical Union (IAU). The IAU officially recognized the Californian team's proposed name Haumea over the name proposed by the Spanish team, Ataecina, in September 2008.

References

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