View source for Hiʻiaka (moon)

{{Short description|Larger moon of Haumea}}
{{Use dmy dates|date=July 2019}}
{{Infobox planet
| name = Hi{{okina}}iaka
| image = Haumea-moons-hubble.gif
| caption = In this series of photos taken by the [[Hubble Space Telescope]], the brighter object Hi{{okina}}iaka is seen orbiting [[Haumea]] (center).
| discoverer = [[Michael E. Brown]], <br> [[Chad Trujillo]], <br> [[David Rabinowitz]], et al.
| discovered = 26 January 2005
| mpc_name = Haumea I
| alt_names = {{mp|(136108) 2003 EL|61}}&nbsp;I<br>{{mp|S|2005|2003 EL|61|1}}
| pronounced = {{IPAc-en|h|iː|ʔ|i|ˈ|ɑː|k|ə}}<br>{{IPA|haw|ˈhiʔiˈjɐkə|lang}}
| 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=°}}
| asc_node = {{val|206.766|0.033|u=°}}
| arg_peri = {{val|154.1|5.8|u=°}}
| mean_anomaly = {{val|152.8|6.1|u=°}}
| 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 = {{val|9.8|u=h|p=~}}<ref name="Hastings2016"/>
| 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/>
}}

'''Hi{{okina}}iaka''' is the larger, outer moon of the trans-Neptunian [[dwarf planet]] [[Haumea]]. It is named after one of the daughters of [[Haumea (mythology)|Haumea]], [[Hi{{okina}}iaka]], the patron goddess of the [[Big Island of Hawaii]]. 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=°}}. Assuming its estimated diameter of over 300&nbsp;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]], and possibly [[Varda I Ilmarë]] and [[Salacia I Actaea]].

==Discovery==
Hi{{okina}}iaka was the first [[natural satellite|satellite]] discovered around Haumea. It was discovered on 26 January 2005 and nicknamed "[[Rudolph the Red-Nosed Reindeer|Rudolph]]" by the discovery team before being assigned an official name.{{cn|date=July 2024}}

== 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 Hiʻiaka 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 Hiʻiaka is not a gravitationally collapsed spheroid; they further suggest that Hiʻiaka is not tidally locked and has a rotation period of about 9.8 hours.<ref name="Hastings2016"/>

=== Mass ===
The mass of Hi{{okina}}iaka is estimated to be {{val|1.79|0.11|e=19|ul=kg}} using precise relative [[astrometry]] from the [[Hubble Space 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 Hi{{okina}}iaka 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/>

==See also==
*[[Namaka (moon)|Namaka]], the other [[Moons of Haumea|moon of Haumea]]

==References==
{{Reflist|30em| refs =
<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 = 4766–4776| arxiv = 0903.4213| bibcode = 2009AJ....137.4766R| s2cid = 15310444}}
</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 |bibcode = 2011A&A...528A.105D |arxiv = 1101.2102 | s2cid = 119226136}}</ref>

<ref name=johnston>{{cite web
| url = http://www.johnstonsarchive.net/astro/astmoons/am-136108.html
| author = Wm. Robert Johnston
| title = (136108) Haumea, Hiʻiaka, and Nāmaka
| date = 17 September 2008
| access-date = 2008-09-18
| archive-date = 21 December 2017
| archive-url = https://web.archive.org/web/20171221043516/http://www.johnstonsarchive.net/astro/astmoons/am-136108.html
| url-status = live
}}</ref>

<ref name="Hastings2016">{{cite journal
  |title      = The Short Rotation Period of Hiʻiaka, Haumea's Largest Satellite
  |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
  |date       = December 2016
  |journal    = The Astronomical Journal
  |volume     = 152
  |issue      = 6
  |id         = 195
  |pages      = 12
  |doi        = 10.3847/0004-6256/152/6/195
  |arxiv      = 1610.04305
  |bibcode    = 2016AJ....152..195H
  |oclc       = 6889796157
  |osti       = 22662917|s2cid = 33292771 |doi-access = free }}</ref>

}}

==External links==
* [http://www.gps.caltech.edu/%7Embrown/papers/ps/EL61.pdf Brown's publication describing the discovery of Hi{{okina}}iaka]
* [http://www.gps.caltech.edu/~mbrown/papers/ps/rudolph.pdf Paper describing the composition of Hi{{okina}}iaka]

{{Moons of plutoids}}
{{Haumea}}
{{Solar System moons (compact)}}

{{DEFAULTSORT:Hi'iaka (moon)}}
[[Category:Moons of Haumea]]
[[Category:Trans-Neptunian satellites]]
[[Category:Discoveries by Michael E. Brown]]
[[Category:Discoveries by Chad Trujillo]]
[[Category:Discoveries by David L. Rabinowitz]]
[[Category:Objects observed by stellar occultation]]