Moons of Haumea: Difference between revisions

[[File:2003 EL61 Haumea, with moons.jpg|thumb|200px|[[Keck telescope|Keck]] image of Haumea and its moons. Hiʻiaka is above Haumea (center), and Namaka is directly below.]]

[[File:Haumea ring moons diagram.png|400px|thumb|Scale diagram of Haumea, the ring, and orbits of its two moons]]

The [[Solar System#Trans-Neptunian region|outer Solar System]] [[dwarf planet]] [[Haumea]] has two known [[Natural satellite|moons]], Hiʻiaka and Namaka, named after [[Hawaiian mythology|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.

Haumea's moons are unusual in a number of ways. They are thought to be part of [[Haumea family|its extended collisional family]], which formed billions of years ago from icy debris after a large impact disrupted Haumea's [[volatiles|ice]] [[Mantle (geology)|mantle]]. Hiʻiaka, the larger, outermost moon, has large amounts of pure water ice on its surface, which is rare among [[Kuiper belt]] objects.<ref name="Barkume2006"/> Namaka, about one tenth the mass, has an orbit with surprising dynamics: it is unusually [[Orbital eccentricity|eccentric]] and appears to be greatly influenced by the larger satellite.

==History==

The outer and larger of the two satellites was discovered January26, 2005,<ref>

{{cite journal

|last-author-amp=yes

|volume=632|date=2005-09-02|pages=L45–L48

|url=http://authors.library.caltech.edu/34486/1/1538-4357_632_1_L45.pdf

}}</ref> and formally designated S/2005 (2003 EL₆₁) 1, though nicknamed "[[Rudolph the Red-Nosed Reindeer|Rudolph]]" by the Caltech team.<ref>

{{cite news

|accessdate=2008-10-12

}}</ref> The smaller, inner satellite of Haumea was discovered on June 30, 2005, formally termed S/2005 (2003 EL₆₁) 2, and nicknamed "[[Blitzen the Reindeer|Blitzen]]".<ref name="RagozzineDPS08"/> 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]] on September17, 2008: (136108) Haumea I Hiʻiaka and (136108) Haumea II Namaka.<ref name="iaunews">

{{cite web

|title=News Release - IAU0807: IAU names fifth dwarf planet Haumea

|accessdate=2008-09-18

}}</ref> Each moon was named after a daughter of [[Haumea (mythology)|Haumea]], the Hawaiian goddess of fertility and childbirth. [[Hiʻiaka]] is the goddess of [[hula|dance]] and patroness of the [[Big Island of Hawaii]], where the [[Mauna Kea Observatory]] is located.<ref name="usgs">

{{cite news

|accessdate=2008-09-17

}}</ref> [[Nāmaka]] is the goddess of water and the sea; she cooled her sister [[Pele (deity)|Pele]]'s lava as it flowed into the sea, turning it into new land.<ref name="craig"/>

In her legend, Haumea's many children came from different parts of her body.<ref name="craig">

{{cite book

|url=https://books.google.com/?id=LOZuirJWXvUC&pg=PA128&dq=haumea

}}</ref> 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 family|Haumea's collisional family]]. There could therefore be additional outer moons, smaller than Namaka, that have not yet been detected. However, [[Hubble Space Telescope|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]]).<ref name="Ragozzine&Brown2009">

{{cite journal

|pages=4766

}}</ref> This makes it unlikely that any more exist.

==Surface properties==

Hiʻiaka is the outer and, at roughly 350&nbsp;km in diameter, the larger and brighter of the two moons.<ref name="Brown2006-discovery">{{cite journal| doi = 10.1086/501524| last1 = Brown| first1 = M. E.| authorlink = Michael E. Brown| last2 = Van Dam| first2 = M. A.| last3 = Bouchez| first3 = A. H.| last4 = Le Mignant| first4 = D.| last5 = Campbell| first5 = R. D.| last6 = Chin| first6 = J. C. Y.| last7 = Conrad| first7 = A.| last8 = Hartman| first8 = S. K.| last9 = Johansson| first9 = E. M.| last10 = Lafon| first10 = R. E.| last11 = Rabinowitz| first11 = D. L. Rabinowitz| last12 = Stomski| first12 = P. J. Jr.| last13 = Summers| first13 = D. M.| last14 = Trujillo| first14 = C. A.| last15 = Wizinowich| first15 = P. L.| year = 2006| title = Satellites of the Largest Kuiper Belt Objects| journal = The Astrophysical Journal| volume = 639| issue = 1| pages = L43–L46| pmid = | pmc = | arxiv = astro-ph/0510029| bibcode = 2006ApJ...639L..43B| url = http://web.gps.caltech.edu/~mbrown/papers/ps/gab.pdf| format = PDF| accessdate = 2011-10-19| ref = {{sfnRef|Brown Van Dam et al.|2006}}

}}</ref> Strong absorption features observed at 1.5, 1.65 and 2 [[micrometre|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.<ref name="largest">

{{cite web

|work=CalTech

|accessdate=2008-09-19

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.<ref name="Fraser09"/> Based on this common albedo, the inner moon, Namaka, which is a tenth the mass of Hiʻiaka, would be about 170&nbsp;km in diameter.<ref name="Johnston">

{{cite web

|accessdate=2009-02-01

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 [[Near Infrared Camera and Multi-Object Spectrometer|NICMOS camera]] has confirmed that the spectral line at 1.6&nbsp;µm that indicates the presence of water ice is at least as strong in the moons' spectra as in Haumea's spectrum.<ref name="Fraser09">

{{cite journal

|volume=695 |pages=L1

}}</ref>

==Orbital characteristics==

[[File:TheKuiperBelt Orbits Haumea moons.svg|thumb|300px|A view of the orbits of Hiʻiaka (blue) and Namaka (green)]]

Hiʻiaka orbits Haumea nearly circularly every 49&nbsp;days.<ref name="Brown2006-discovery"/> Namaka orbits Haumea in 18 days in a moderately elliptical, [[Osculating orbit|non-Keplerian]] orbit, and as of 2008 was inclined 13° with respect to Hiʻiaka, which [[Perturbation (astronomy)|perturbs]] its orbit.<ref name="RagozzineDPS08"/> Because the impact that created the moons of Haumea is thought to have occurred in the early history of the Solar System,<ref name="BrownBarkume2007">

{{cite journal

}}</ref> over the following billions of years it should have been [[tidal acceleration|tidally damped]] into a more circular orbit. Namaka's orbit has likely been disturbed by [[orbital resonance]]s with the more-massive Hiʻiaka due to converging orbits as they moved outward from Haumea due to [[tidal acceleration|tidal dissipation]].<ref name="RagozzineDPS08"/> 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 [[orbital resonance|resonance]].<ref name="RagozzineDPS08"/> This resonance strongly perturbs Namaka's orbit, which has a current [[Precession (astronomy)#Anomalistic precession|precession]] of its [[argument of periapsis]] by about −6.5° per year, a precession period of 55 years.<ref name="Ragozzine&Brown2009"/>

At present, the orbits of the Haumean moons appear almost exactly edge-on from Earth, with Namaka having periodically [[occultation|occulted]] Haumea from 2009 to 2011.<ref name="IAU8949">

{{cite web

|date = 2008-09-17

|accessdate = 2008-12-06

|deadurl = yes

|archiveurl = https://web.archive.org/web/20090111105134/http://www.cfa.harvard.edu/~fabrycky/EL61/

|archivedate = 11 January 2009

}}</ref><ref name="events09">

{{cite web

|accessdate=2009-02-18

}}</ref> Observation of such transits would provide precise information on the size and shape of Haumea and its moons, as [[Solar eclipses on Pluto|happened in the late 1980s]] with Pluto and [[Charon (moon)|Charon]].<ref>

{{cite book

|url=https://books.google.com/?id=G7UtYkLQoYoC&pg=PA545&lpg=PA545&dq=mutual+event+pluto

|accessdate=2008-10-17

}}</ref> The tiny change in brightness of the system during these occultations required at least a [[Optical telescope#Astronomical research telescopes|medium]]-[[aperture]] [[List of optical telescopes|professional telescope]] for detection.<ref name="FabryckyDPS08">

{{cite web |author=D. C. Fabrycky |display-authors=4 |author2=M. J. Holman |author3=D. Ragozzine |author4=M. E. Brown |author5=T. A. Lister |author6=D. M. Terndrup |author7=J. Djordjevic |author8=E. F. Young |author9=L. A. Young |author10=R. R. Howell |title=Mutual Events of 2003 EL61 and its Inner Satellite |url=http://adsabs.harvard.edu/abs/2008DPS....40.3608F |work=AAS DPS conference 2008 |accessdate=14 November 2018}}</ref> Hiʻiaka last occulted Haumea in 1999, a few years before its discovery, and will not do so again for some 130 years.<ref name="shadows">

{{cite web

|accessdate=2008-09-27

}}</ref> However, in a situation unique among [[regular moon|regular satellite]]s, the great [[Precession (astronomy)#Anomalistic precession|torquing]] of Namaka's orbit by Hiʻiaka preserved the viewing angle of Namaka–Haumea transits for several more years.<ref name="RagozzineDPS08">

{{cite web

|accessdate = 2008-10-17

|deadurl = yes

|archiveurl = https://web.archive.org/web/20130718182107/http://www.abstractsonline.com/viewer/viewAbstract.asp?CKey=%7B421E1C09-F75A-4ED0-916C-8C0DDB81754D%7D&MKey=%7B35A8F7D5-A145-4C52-8514-0B0340308E94%7D&AKey=%7BAAF9AABA-B0FF-4235-8AEC-74F22FC76386%7D&SKey=%7B545CAD5F-068B-4FFC-A6E2-1F2A0C6ED978%7D

|archivedate = 18 July 2013

}}</ref><ref name="FabryckyDPS08"/>

<center>

{| class="wikitable" border="1"

! Order<br><ref group=note>Order refers to the position with respect to their average distance from Haumea.</ref><br>

! colspan="3" | Name<br>([[Help:IPA for English|pronunciation]])<br><ref group=note>Label refers to the [[Roman numeral]] attributed to each moon in order of their discovery.</ref><br>

! Mean diameter<br>(km)

! Mass<br>(×10¹⁸&nbsp;kg)

! Semi-major<br>axis (km)

! Orbital period<br>(days)

! Inclination (°)

| 0 || colspan=3| (ring) || ≈&thinsp;70 || || {{val|2285|8}}<ref name="Ortiz2017"/> || {{val|0.489438|0.000012}}<ref name="Ortiz2017">{{cite journal|display-authors= 3|last1= Ortiz|first1=J. L.|last2= Santos-Sanz|first2=P.|last3= Sicardy|first3= B.|last4= Benedetti-Rossi|first4= G.|last5= Bérard|first5= D.|last6= Morales|first6= N.|last7= Duffard|first7= R.|last8= Braga-Ribas|first8=F.|last9= Hopp|first9=U.|last10= Ries|first10=C.|last11= Nascimbeni|first11=V.|last12= Marzari|first12=F.|last13= Granata|first13=V.|last14= Pál|first14=A.|last15= Kiss|first15=C.|last16= Pribulla|first16=T.|last17=Komžík|first17=R.|last18= Hornoch|first18=K.|last19=Pravec|first19=P.|last20= Bacci|first20=P.|last21= Maestripieri|first21= M.|last22= Nerli|first22=L.|last23=Mazzei|first23=L.|last24= Bachini|first24=M.|last25=Martinelli|first25= F.|last26=Succi|first26= G.|last27=Ciabattari|first27=F.|last28= Mikuz|first28=H.|last29=Carbognani|first29= A.|last30=Gaehrken|first30=B.|last31= Mottola|first31=S.|last32= Hellmich|first32=S.|last33=Rommel|first33=F. L.|last34=Fernández-Valenzuela|first34=E.|last35= Bagatin|first35=A. Campo|last36=Cikota|first36= S.|last37=Cikota|first37=A.|last38=Lecacheux|first38=J.|last39=Vieira-Martins|first39=R.|last40=Camargo|first40=J. I. B.|last41=Assafin|first41=M.|last42= Colas|first42=F.|last43=Behrend|first43= R.|last44=Desmars|first44=J.|last45=Meza|first45=E.|last46=Alvarez-Candal|first46=A.|last47=Beisker|first47=W.|last48= Gomes-Junior|first48=A. R.|last49= Morgado|first49=B. E.|last50=Roques|first50=F.|last51= Vachier|first51=F.|last52=Berthier|first52= J.|last53=Mueller|first53=T. G.|last54=Madiedo|first54=J. M.|last55=Unsalan|first55=O.|last56= Sonbas|first56=E.|last57=Karaman|first57= N.|last58=Erece|first58=O.|last59=Koseoglu|first59=D. T.|last60=Ozisik|first60=T.|last61= Kalkan|first61=S.|last62= Guney|first62=Y.|last63=Niaei|first63=M. S.|last64=Satir|first64=O.|last65= Yesilyaprak|first65=C.|last66= Puskullu|first66=C.|last67=Kabas|first67= A.|last68=Demircan|first68= O.|last69=Alikakos|first69=J.|last70= Charmandaris|first70=V.|last71=Leto|first71=G.|last72=Ohlert|first72=J.|last73=Christille|first73=J. M.|last74=Szakáts|first74=R.|last75=Farkas|first75=A. Takácsné|last76=Varga-Verebélyi|first76=E.|last77= Marton|first77=G.|last78=Marciniak|first78= A.|last79=Bartczak|first79=P.|last80=Santana-Ros|first80=T.|last81=Butkiewicz-Bąk|first81=M.|last82=Dudziński|first82=G.|last83=Alí-Lagoa|first83=V.|last84= Gazeas|first84=K.|last85= Tzouganatos|first85=L.|last86=Paschalis|first86=N.|last87=Tsamis|first87=V.|last88=Sánchez-Lavega|first88=A.|last89=Pérez-Hoyos|first89=S.|last90= Hueso|first90=R.|last91=Guirado|first91=J. C.|last92=Peris|first92=V.|last93=Iglesias-Marzoa|first93=R.|title=The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation|journal= Nature|volume= 550|issue= 7675|year= 2017|pages= 219–223|doi= 10.1038/nature24051|pmid= 29022593|bibcode=2017Natur.550..219O}}</ref><ref name="ring-period" group=lower-alpha>Based on a 3:1 resonance with Haumea's rotation period.</ref> || || ≈&thinsp;0 || January 2017

| 1 || Haumea&nbsp;II || Namaka || {{IPA|/nɑːˈmɑːkə/}} || ≈&thinsp;170? || {{val|1.79|1.48}}<ref name="Ragozzine&Brown2009"/> <br>(≈&thinsp;0.05% Haumea) || {{val|25657|91}}<ref name="Ragozzine&Brown2009"/>|| {{val|18.2783|0.0076}}<ref name="Ragozzine&Brown2009"/><ref group=note name=kepler>Using [[Kepler's laws of planetary motion#Third law|Kepler's third law]].</ref> || {{val|0.249|0.015}}<ref name="Ragozzine&Brown2009"/><ref <ref group=note name=perturb>As of 2008: Namaka's eccentricity and inclination are [[Kozai mechanism|variable]] due to perturbation.</ref> || {{val|113.013|0.075}}<ref name="Ragozzine&Brown2009"/> <br>({{val|13.41|0.08}} from Hiʻiaka)<ref group=note name=perturb/>|| June 2005

| 2 || Haumea&nbsp;I || Hiʻiaka || {{IPA|/hiːʔiːˈɑːkə/}} || ≈&thinsp;310 || {{val|17.9|1.1}}<ref name="Ragozzine&Brown2009"/> <br>(≈&thinsp;0.5% Haumea) || {{val|49880|198}}<ref name="Ragozzine&Brown2009"/> || {{val|49.462|0.083}}<ref name="Ragozzine&Brown2009"/><ref group=note name=kepler/> || {{val|0.0513|0.0078}}<ref name="Ragozzine&Brown2009"/> || {{val|126.356|0.064}}<ref name="Ragozzine&Brown2009"/> || January 2005

|}</center>

== Namaka ==

{{Infobox planet

| name = Namaka

| image = 2003 EL61 Haumea, with moons.jpg

| caption = Namaka is the faint spot near the bottom of the photo, directly below [[Haumea]] (center), in this [[Keck telescope]] image.

| discoverer = [[Michael E. Brown]], <br> [[Chad Trujillo]], <br> [[David Rabinowitz]], et al.

| discovered = 30 June 2005

| mpc_name = Haumea II Namaka

| pronounced = {{IPAc-en|n|ɑː|ˈ|m|ɑː|k|ə}} {{respell|nah|MAH|kə}}<ref name="pron" group=lower-alpha>The [[Hawaiian language|Hawaiian]] pronunciation is {{IPA-haw|naːˈmɐkə|}}.</ref>

| alt_names = {{mp|(136108) 2003 EL|61}}&nbsp;II, <br> {{mp|S|2005|2003 EL|61|2}}

| orbit_ref = <ref name="SatelliteOrbits"/>

| epoch = [[Julian day|JD]] 2454615.0

| semimajor = {{val|25657|91|u=km}}<ref name=SatelliteOrbits/>

| eccentricity = {{val|0.249|0.015}} (in 2009; [[Kozai mechanism|variable]])

| period = {{val|18.2783|0.0076|u=d}}<ref name=SatelliteOrbits/>

| inclination = {{val|113.013|0.075|u=°}}<br>{{val|13.41|0.08|u=°}} relative to [[Hiʻiaka (moon)|Hiʻiaka]] (in 2008; [[Kozai mechanism|variable]])

| asc_node = {{val|205.016|0.228|u=°}}

| arg_peri = {{val|178.9|2.3|u=°}}

| mean_anomaly = {{val|178.5|1.7|u=°}}

| satellite_of = {{dp|Haumea}}

| mean_radius = ~85 km (if albedo is same as primary's 0.7±0.1)

| mass = 1.79 ± 1.48{{e|18}} [[Kilogram|kg]]<ref name="SatelliteOrbits"/> <br> (0.05% the mass of Haumea)

| density = (assumed to be near 1 g/cm³)

| single_temperature = 32±3 [[Kelvin|K]]

| rotation =

| axial_tilt =

| albedo = {{val|0.8|0.2}}<ref name=johnston/><ref name=RagozzineBrown2009/>

| magnitude = 21.9 (4.6 difference from primary's 17.3)<ref name=johnston/>

}}

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 (mythology)|Haumea]].

=== Discovery ===

Namaka was discovered on 30 June 2005 and announced on 29 November 2005.<ref name="IAUC_8636" /> It was nicknamed "[[Blitzen the Reindeer|Blitzen]]" by the discovery team before being assigned an official name.

=== Physical characteristics ===

Namaka is only 1.5% as bright as its parent dwarf planet Haumea<ref name="Barkume2006" /> and is about 0.05% its mass. If it turns out to have a similar [[albedo]], it would be about 170&nbsp;km in diameter.<ref name=johnston/> Photometric observations indicate that its surface is made of water ice.<ref name="Barkume2006" /> Mutual events between 2009 and 2011<ref name="events09"/> were expected to improve the knowledge of the orbits and masses of the components of the Haumean system,<ref name=RagozzineBrown2009/> but interpreting those observations was greatly complicated by the unexpected non-tidally locked spin state of Hiʻiaka. Further observations of Hiʻiaka might allow to determine its rotation period and spin state more precisely, at which point it should be possible to remove its effect from the data obtained in 2009.<ref>{{Cite journal|title=The Short Rotation Period of Hi'iaka, Haumea's Largest Satellite|journal=The Astronomical Journal|volume=152|issue=6|pages=195|language=en|access-date=|arxiv=1610.04305|last1=Hastings|first1=Danielle M|last2=Ragozzine|first2=Darin|last3=Fabrycky|first3=Daniel C|last4=Burkhart|first4=Luke D|last5=Fuentes|first5=Cesar|last6=Margot|first6=Jean-Luc|last7=Brown|first7=Michael E|last8=Holman|first8=Matthew|year=2016|doi=10.3847/0004-6256/152/6/195|bibcode=2016AJ....152..195H}}</ref><ref>{{Cite journal|arxiv=1204.3923|last1=Grundy|first1=W. M|title=Mutual Events in the Cold Classical Transneptunian Binary System Sila and Nunam|journal=Icarus|volume=220|pages=74|last2=Benecchi|first2=S. D|last3=Rabinowitz|first3=D. L|last4=Porter|first4=S. B|last5=Wasserman|first5=L. H|last6=Skiff|first6=B. A|last7=Noll|first7=K. S|last8=Verbiscer|first8=A. J|last9=Buie|first9=M. W|last10=Tourtellotte|first10=S. W|last11=Stephens|first11=D. C|last12=Levison|first12=H. F|year=2012|doi=10.1016/j.icarus.2012.04.014|bibcode=2012Icar..220...74G}}</ref>

== Hiʻiaka ==

{{Infobox planet

| name = Hiʻiaka

| image = 2003 EL61 Haumea, with moons.jpg

| caption = Hiʻiaka is above Haumea (center) in this [[Keck telescope]] image.

| discoverer = [[Michael E. Brown]], <br> [[Chad Trujillo]], <br> [[David Rabinowitz]], et al.

| discovered = 26 January 2005

| mpc_name = Haumea I Hiʻiaka

| alt_names = {{mp|(136108) 2003 EL|61}}&nbsp;I, <br>{{mp|S|2005|2003 EL|61|1}}

| pronounced = {{IPAc-en|ˌ|h|iː|ʔ|i|ˈ|ɑː|k|ə}}<ref name="pron2" group=lower-alpha>The [[Hawaiian language|Hawaiian]] pronunciation is {{IPA-haw|ˈhiʔiˈjɐkə|}}.</ref>

| orbit_ref = <ref name=RagozzineBrown2009/>

| semimajor = {{val|49880|198|ul=km}}

| eccentricity = {{val|0.0513|0.0078}}

| period = {{val|49.12|0.03|u=days}}

| inclination = {{val|126.356|0.064|s=°}}

| satellite_of = {{dp|Haumea}}

| mean_radius = {{val|p=~|160|u=km}}<ref name=RagozzineBrown2009/>

| mass = {{val|1.79|0.11|e=19|ul=kg}}<ref name=RagozzineBrown2009/> (0.45% of Haumea)

| density = {{val|p=~|1|ul=g/cm3}}

| single_temperature = {{val|32|3|ul=K}}

| rotation =

| axial_tilt =

| albedo = {{val|0.8|0.07}}<ref name=johnston/><ref name=RagozzineBrown2009/>

| magnitude = 20.3 (3.0 difference from primary's 17.3)<ref name=johnston/>

}}

Hiʻiaka is the larger, outer moon of the [[dwarf planet]] [[Haumea]].

=== Discovery and naming ===

Hiʻiaka was the first [[natural satellite|satellite]] discovered around Haumea. It is named after one of the daughters of [[Haumea (mythology)|Haumea]], [[Hiʻiaka]], the patron goddess of the [[Big Island of Hawaii]], though at first it had gone by the nickname "[[Rudolph the Red-Nosed Reindeer|Rudolph]]" by its discovery team. It orbits once every {{val|49.12|0.03|u=days}} at a distance of {{val|49880|198|ul=km}}, with an eccentricity of {{val|0.0513|0.0078}} and an inclination of {{val|126.356|0.064|s=°}}.

=== Physical characteristics ===

==== Size and brightness ====

Its measured brightness is {{val|5.9|0.5|s=%}}, translating into a diameter of about 22% of its primary, or in the range of {{val|320|u=km}}, assuming similar infrared albedo.<ref name=RagozzineBrown2009/> To put this in perspective, if Hi'iaka were in the asteroid belt, it would be larger than all but the [[List of notable asteroids#Largest by diameter|four]] largest asteroids, after [[1 Ceres]], [[2 Pallas]], [[4 Vesta]], and [[10 Hygiea]]. 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.<ref>{{Cite web|url=http://www.planetary.org/blogs/guest-blogs/2016/1017-rapidly-rotating-regular-satellites-and-tides.html|title=Rapidly Rotating Regular Satellites and Tides|author=Ragozzine, D.|date=2016-10-17|website=www.planetary.org|language=en|access-date=2018-11-14}}</ref>

==== Mass ====

The mass of Hiʻiaka is estimated to be {{val|1.79|0.11|e=19|ul=kg}} using precise relative [[astrometry]] from [[Hubble Telescope]] and [[Keck Telescope]] and applying [[3-body problem|3-body]], point-mass model to the Haumean system.<ref name=RagozzineBrown2009/>

==== Spectrum and composition ====

The near infrared spectrum of Hiʻiaka 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 {{val|1.65|u=μm}} indicates that the surface water 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 ray]]s.<ref name=Dumas2011/>

==Notes==

==References==

<ref name="SatelliteOrbits">

{{cite journal| doi = 10.1088/0004-6256/137/6/4766| last1 = Ragozzine| first1 = D.| last2 = Brown| first2 = M. E.| year = 2009| title = Orbits and Masses of the Satellites of the Dwarf Planet Haumea (2003 EL61)| journal = The Astronomical Journal| volume = 137| issue = 6| pages = 4766| pmid = | pmc = | arxiv = 0903.4213| bibcode = 2009AJ....137.4766R| ref = harv}}

</ref>

<ref name="RagozzineBrown2009">

{{cite journal| doi = 10.1088/0004-6256/137/6/4766| last1 = Ragozzine| first1 = D.| last2 = Brown| first2 = M. E.| year = 2009| title = Orbits and Masses of the Satellites of the Dwarf Planet Haumea (2003 EL61)| journal = The Astronomical Journal| volume = 137| issue = 6| pages = 4766| pmid = | pmc = | arxiv = 0903.4213| bibcode = 2009AJ....137.4766R| ref = harv}}

</ref>

<ref name="Dumas2011">{{Cite journal | last1 = Dumas | first1 = C.| last2 = Carry | first2 = B.| last3 = Hestroffer | first3 = D.| last4 = Merlin | first4 = F.| title = High-contrast observations of (136108) Haumea | doi = 10.1051/0004-6361/201015011 | journal = Astronomy & Astrophysics | volume = 528 | pages = A105 | year = 2011 | pmid = | pmc = |bibcode = 2011A&A...528A.105D |arxiv = 1101.2102 }}</ref>

<ref name=johnston>

{{cite web

| url = http://www.johnstonsarchive.net/astro/astmoons/am-136108.html

| author = Wm. Robert Johnston

| title = (136108) Haumea, Hi'iaka, and Nāmaka

| date = 2008-09-17

| accessdate = 2008-09-18

</ref>

<ref name="IAUC_8636">

{{cite web

|last = Green

|first = Daniel W. E.

|date = 1 December 2005

|title = IAUC 8636

|url = http://www.cbat.eps.harvard.edu/iauc/08600/08636.html

|access-date=14 November 2018

}}

</ref>

<ref name="Barkume2006">{{Cite journal | last1 = Barkume | first1 = K. M. | last2 = Brown | first2 = M. E. | last3 = Schaller | first3 = E. L. | title = Water Ice on the Satellite of Kuiper Belt Object 2003 EL61 | doi = 10.1086/503159 | journal = The Astrophysical Journal | volume = 640 | pages = L87–L89 | year = 2006 | pmid = | pmc =| url = http://www.gps.caltech.edu/~mbrown/papers/ps/rudolph.pdf|arxiv = astro-ph/0601534 |bibcode = 2006ApJ...640L..87B }}</ref>

}}

==External links==

* [http://www.gps.caltech.edu/~darin/haumeasatsanim.gif Animation of the orbits of Haumea's moons]

* [[International Year of Astronomy|International Year of Astronomy 2009]] [http://365daysofastronomy.org/2009/03/31/march-31st/ podcast: Dwarf Planet Haumea (Darin Ragozzine)]

{{good article}}

{{Use dmy dates|date=September 2010}}