View source for Haumea

{{Short description|Dwarf planet in the Solar System}}
{{About|the dwarf planet|the Hawaiian goddess|Haumea (mythology)|other uses}}
{{Featured article}}
{{Infobox planet
| minorplanet = yes
| background = #C2E0FF
| name = 136108 Haumea
| symbol = [[File:Haumea symbol (bold).svg|24px|alt=🝻|Planetary symbol for Haumea]] (mostly astrological)
| image = Haumea Hubble.png
| caption = Low-resolution [[Hubble Space Telescope]] image of Haumea and its two moons, [[Hiʻiaka (moon)|Hiʻiaka]] (top) and [[Namaka (moon)|Namaka]] (bottom), June 2015
| discoverer = {{Ubl
 | [[Michael E. Brown|Brown]] et al.
 | [[José Luis Ortiz Moreno|Ortiz]] et al.
 }}
| discovered = {{Ubl
| 7 March 2003 (Ortiz)
| 28 December 2004 (Brown)
  }}
| earliest_precovery_date = 22 March 1955
| mpc_name = (136108) Haumea
| pronounced = {{IPAc-en|h|aʊ|ˈ|m|eɪ|.|ə|,_|ˌ|h|ɑː|uː|-}}{{refn|{{respell|how|MAY|ə}}, with three syllables according to the English pronunciation in [[Hawaii]],<ref>[http://www.heraldnet.com/article/20080919/NEWS02/709199740 ''New dwarf planet named for Hawaiian goddess''] {{webarchive|url=https://web.archive.org/web/20151208204927/http://www.heraldnet.com/article/20080919/NEWS02/709199740 |date=2015-12-08 }} (HeraldNet, 19 September 2008)</ref> or {{respell|HAH|oo|MAY|ə}} with four syllables according to Brown's students.<ref>{{cite web |url=http://dps08.astro.cornell.edu/AAS_WebcastSchedule_2008.html |title=DPS08 Webstreaming |access-date=2009-02-14  |archive-url=https://web.archive.org/web/20090106032448/http://dps08.astro.cornell.edu/AAS_WebcastSchedule_2008.html |archive-date=2009-01-06 }}</ref><ref>{{cite web|url=http://365daysofastronomy.org/2009/03/31/march-31st/|title=365 Days of Astronomy|date=31 March 2009 |archive-url=https://web.archive.org/web/20120220034436/http://365daysofastronomy.org/2009/03/31/march-31st/|archive-date=2012-02-20|access-date=2009-04-11}}</ref>|group=nb}}
| adjectives = Haumean<ref>E.g. Giovanni Vulpetti (2013) ''Fast Solar Sailing'', p. 333.</ref>
| note = yes
| alt_names = {{mp|2003 EL|61}}
| named_after = [[Haumea (mythology)|Haumea]]
| mp_category = {{Ubl
 | [[Dwarf planet]]
 | [[Trans-Neptunian object|TNO]]<ref name="K10H75" /><ref name="Buie" />
 | [[Haumea family]]
 | [[minor planet moon|trinary]]<ref name="candidate" />
 }}
| orbit_ref = <ref name="MPC-object" />
| epoch = 17 December 2020 ([[Julian day|JD]] 2459200.5)
| uncertainty = 2
| observation_arc = {{time interval|1955-03-22|2021-01-07|show=yd}} ({{time interval|1955-03-22|2021-01-07|show=d}})
| aphelion = {{cvt|51.585|AU|Tm|lk=on}}
| perihelion = {{cvt|34.647|AU|Tm}}
| time_periastron = ≈ 1 June 2133<ref name=perihelion/><br />±2 days
| semimajor = {{cvt|43.116|AU|Tm}}
| eccentricity = 0.19642
| period = 283.12 [[Julian year (astronomy)|yr]] (103,410 days)<ref name="jpldata"/>
| mean_anomaly = 218.205[[Degree (angle)|°]]
| mean_motion = {{Deg2DMS|0.00348140|sup=ms}} / day
| inclination = 28.2137°
| asc_node = 122.167°
| arg_peri = 239.041°
| avg_speed = {{val|4.53|u=km/s}}{{refn|name=orbitspeed|group=nb|Assuming a [[circular orbit]] with negligible eccentricity, the mean [[orbital speed]] can be approximated by the time {{mvar|T}} it takes to complete one revolution around its orbital [[circumference]], with the radius being its [[semi-major axis]] {{mvar|a}}: &nbsp;<math>v \approx {2 \pi a \over T}</math>.}}
| satellites = [[Moons of Haumea|2]] ([[Hiʻiaka (moon)|Hiʻiaka]] and [[Namaka (moon)|Namaka]])
| dimensions = {{Ubl
 | ≈ 2,100&thinsp;×&thinsp;1,680&thinsp;×&thinsp;1,074&thinsp;km{{refn|Best fit physical model assuming [[hydrostatic equilibrium]] for Haumea.<ref name="Dunham2019" />|name=HE|group=nb}}<ref name="Dunham2019" />
 | {{val|2322|60|fmt=commas}}&thinsp;×&thinsp;{{val|1704|8|fmt=commas}}&thinsp;×&thinsp;{{val|1026|32|fmt=commas}}&thinsp;km{{refn|Occultation-derived model based on the assumption Haumea's ring does not contribute to its total brightness.<ref name="Ortiz2017" />|group=nb}}<ref name="Ortiz2017" />
 }}
| mean_radius = {{Ubl
 | ≈&thinsp;{{val|780|u=km}}{{refn|name=HE|group=nb}}
 | {{val|798|6|u=km}} to {{val|816|u=km}}{{refn|name=Ortiz|group=nb}}
 }}
| surface_area = ≈ {{val|8.14|e=6|u=km2}}{{refn|name=HE|group=nb}}<ref name="Wolfram1">{{cite web|url=https://www.wolframalpha.com/input/?i=ellipsoid+surface+area+semi-axis+lengths+1050+840+537|title=Ellipsoid surface area: 8.13712×10^6&nbsp;km<sup>2</sup>|website=wolframalpha.com|date=20 December 2019|access-date=20 December 2019|archive-date=25 July 2020|archive-url=https://web.archive.org/web/20200725052021/https://www.wolframalpha.com/input/?i=ellipsoid+surface+area+semi-axis+lengths+1050+840+537|url-status=live}}</ref>
| volume = ≈ {{val|1.98|e=9|u=km3}}{{refn|name=HE|group=nb}}<ref name="Wolfram2">{{cite web|url=https://www.wolframalpha.com/input/?i=ellipsoid+volume+semi-axis+lengths+1050+840+537|title=Ellipsoid volume: 1.98395×10^9&nbsp;km<sup>3</sup>|website=wolframalpha.com|date=20 December 2019|access-date=20 December 2019|archive-date=25 July 2020|archive-url=https://web.archive.org/web/20200725054507/https://www.wolframalpha.com/input/?i=ellipsoid+volume+semi-axis+lengths+1050+840+537|url-status=live}}</ref><br />{{val|0.0018|u=[[Earth mass|Earths]]}}
| mass = {{val|4.006|0.040|e=21|u=kg}}<ref name="RagozzineBrown2009" /><br />{{val|0.00066|u=[[Earth mass|Earths]]}}
| density = {{Ubl
 | ≈ {{val|2.018|u=g|up=cm3}}{{refn|name=HE|group=nb}}
 | {{val|1.885|0.080|u=g|up=cm3}} to {{val|1.757|u=g|up=cm3}}{{refn|Occultation-derived model based on the upper-limit assumption that Haumea's ring contributes 5% to its total brightness.<ref name="Ortiz2017" />|name=Ortiz|group=nb}}
 }}
| surface_grav = {{Gr|4.006|537|2}} m/s<sup>2</sup> at poles<br />{{nowrap|to {{Gr|4.006|1050|2}} m/s<sup>2</sup> at longest axis}}
| escape_velocity = {{V2|4.006|537|2}} km/s at poles<br />{{nowrap|to {{V2|4.006|1050|2}} km/s at longest axis}}
| sidereal_day = {{val|3.915341|0.000005|u=h}}<ref name="TNOsCool12"/><br />({{val|0.163139208|u=d}})
| axial_tilt = ≈ 126° (to orbit; assumed)<br/>81.2° or 78.9° (to [[ecliptic]]){{refn|name=pole|group=nb|Kondratyev and Kornoukhov (2018) give Haumea's north pole orientation in terms of [[equatorial coordinates]], where  {{mvar|α}}  is [[right ascension]] and  {{mvar|δ}}  is [[declination]].<ref name="Kondratyev2018"/>{{rp|page=3174}} [[Astronomical coordinate systems#Equatorial ↔ ecliptic|Transforming]] equatorial coordinates to [[ecliptic coordinates]] gives  {{mvar|λ}} ≈ 282.5° and  {{mvar|β}} ≈ 9.9° for the first solution of ({{mvar|α}}, {{mvar|δ}}) {{=}} (282.6°, –13.0°), or {{mvar|λ}} ≈ 282.6° and {{mvar|β}} ≈ 11.1° for the second solution of ({{mvar|α}}, {{mvar|δ}}) {{=}} (282.6°, –11.8°).<ref name="coordstransform"/> The [[ecliptic latitude]],  {{mvar|β}},  is the angular offset from the [[ecliptic plane]], whereas [[inclination]]  {{mvar|i}}  with respect to the ecliptic is the angular offset from the [[ecliptic north pole]] at {{nowrap| {{mvar|β}} {{=}} +90° ;}}  {{mvar|i}}  with respect to the ecliptic would be the [[Angle#Combining angle pairs|complement]] of  {{mvar|β}}, which is expressed by the difference {{nowrap| {{mvar|i}} {{=}} 90° – {{mvar|β}}}}. Thus, Haumea's axial tilt is 81.2° or 78.9° with respect to the ecliptic, for the first and second  {{mvar|β}}  values, respectively.}}
| right_asc_north_pole = {{val|282.6|1.2|u=deg}}<ref name="Kondratyev2018" />{{rp|page=3174}}
| declination = {{val|-13.0|1.3|u=deg}} or {{val|-11.8|1.2|u=deg}}<ref name="Kondratyev2018" />{{rp|page=3174}}
| spectral_type = {{Ubl
 | [[Trans-Neptunian object#Spectral type|BB]] ([[Trans-Neptunian object#Color indices|neutral]])
 | B−V {{=}} 0.64, V−R {{=}} 0.33&thinsp;<ref name="Snodgrass2009" />
 | B<sub>0</sub>−V<sub>0</sub> {{=}} 0.646&thinsp;<ref name="Rabinowitz2008" />
 }}
| magnitude = 17.3 ([[Opposition (astronomy)|opposition]])<ref name="AstDys" /><ref name="Horizons"/>
| abs_magnitude = {{val|0.428|0.011}} ([[UBV photometric system|V-band]])&thinsp;<ref name="TNOsCool12" />{{·}}{{val|0.2}}&thinsp;<ref name="jpldata" />
| albedo = {{Ubl
 | ≈&thinsp;0.66 [[geometric albedo|geometric]]{{refn|name=HE|group=nb}}
 | ≤&thinsp;{{val|0.51|0.02}} geometric<ref name="Ortiz2017" />
 | {{val|0.33|0.03}} [[Bond albedo|Bond]]<ref name="Verbiscer2022"/>
 }}
| single_temperature = <&thinsp;50&nbsp;[[kelvin|K]]<ref name="Trujillo 2006" />
}}

'''Haumea''' ([[minor-planet designation]]: '''136108 Haumea''') is a [[dwarf planet]] located [[trans-Neptunian object|beyond]] [[Neptune]]'s orbit.<ref name="iau" /> It was discovered in 2004 by a team headed by [[Michael E. Brown|Mike Brown]] of [[Caltech]] at the [[Palomar Observatory]], and formally announced in 2005 by a team headed by [[José Luis Ortiz Moreno]] at the [[Sierra Nevada Observatory]] in [[Spain]], who had discovered it that year in precovery images taken by the team in 2003. From that announcement, it received the provisional designation 2003 EL61.

On 17 September 2008, it was named after [[Haumea (mythology)|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 [[List of Solar System objects by size|third-largest known trans-Neptunian object]], after [[Eris (dwarf planet)|Eris]] and [[Pluto]], and approximately the size of Uranus's moon [[Titania (moon)|Titania]]. Precovery images of Haumea have been identified back to 22 March 1955.<ref name="jpldata" />

Haumea's mass is about one-third that of Pluto and 1/1400 that of [[Earth]]. Although its shape has not been directly observed, calculations from its [[light curve]] are consistent with it being a [[Jacobi ellipsoid]] (the shape it would be if it were a dwarf planet), with its major [[Axis of rotation|axis]] twice as long as its minor. In October 2017, astronomers announced the discovery of a [[ring system]] around Haumea, representing the first ring system discovered for a [[trans-Neptunian object]] and a dwarf planet.

Haumea's gravity was until recently thought to be sufficient for it to have relaxed into [[hydrostatic equilibrium]], though that is now unclear. Haumea's elongated shape together with its rapid [[rotation]], rings, and high [[albedo]] (from a surface of crystalline water ice), are thought to be the consequences of a [[Impact event|giant collision]], which left Haumea the largest member of a [[collisional family]] (the [[Haumea family]]) that includes several large [[trans-Neptunian object]]s and Haumea's two known moons, [[Moons of Haumea|Hiʻiaka and Namaka]].

==History==

=== Discovery ===
{{main|Controversy over the discovery of Haumea}}
Two teams claim credit for the discovery of Haumea. A team consisting of [[Michael E. Brown|Mike Brown]] of Caltech, [[David L. Rabinowitz|David Rabinowitz]] of Yale University, and [[Chad Trujillo]] of [[Gemini Observatory]] in Hawaii discovered Haumea on 28 December 2004, on images they had taken on 6 May 2004. On 20 July 2005, they published an online abstract of a report intended to announce the discovery at a conference in September 2005.<ref name="trail"/>

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 7–10 March 2003.<ref name="Sanz"/> Ortiz emailed the [[Minor Planet Center]] with their discovery on the night of 27 July 2005.<ref name="Sanz" />

Brown initially conceded discovery credit to Ortiz,<ref>[[Michael E. Brown]]. ''[[How I Killed Pluto and Why It Had It Coming]]'', chapter 9: "The Tenth Planet"</ref> but came to suspect the Spanish team of fraud upon learning that the Spanish observatory had accessed Brown's observation logs the day before the discovery announcement, a fact that they did not disclose in the announcement as would be customary. Those logs included enough information to allow the Ortiz team to [[precovery|precover]] Haumea in their 2003 images, and they were accessed again just before Ortiz scheduled telescope time to obtain confirmation images for a second announcement to the MPC on 29 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.<ref name="ortiz1" />

IAU protocol is that discovery credit for a [[minor planet]] goes to whoever first submits a report to the MPC ([[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 17 September 2008, that Haumea had been named by a dual committee established for bodies expected to be dwarf planets, did not mention a discoverer. The location of discovery was listed as the Sierra Nevada Observatory of the Spanish team,<ref name="usgs" /><ref name="marsden" /> but the chosen name, Haumea, was the Caltech proposal. Ortiz's team had proposed "[[Ataecina]]", the ancient Iberian goddess of spring;<ref name="Sanz" /> as a [[chthonic deity]], it would have been appropriate for a [[plutino]], which Haumea was not.

=== Name and symbol ===

Until it was given a permanent name, the Caltech discovery team used the nickname "[[Santa Claus|Santa]]" among themselves, because they had discovered Haumea on 28 December 2004, just after Christmas.<ref name="Santa2005" /> The Spanish team were the first to file a claim for discovery to the [[Minor Planet Center]], in July 2005. On 29 July 2005, Haumea was given the [[Provisional designation in astronomy|provisional designation]] '''2003&nbsp;EL<sub>61</sub>''', based on the date of the Spanish discovery image. On 7 September 2006, it was numbered and admitted into the official minor planet catalog as (136108) 2003&nbsp;EL<sub>61</sub>.

Following [[Committee on Small Body Nomenclature|guidelines]] established at the time<!--relaxed to a preference in late 2019--> by the IAU that [[classical Kuiper belt object]]s be given names of mythological beings associated with creation,<ref name="IAU-Naming of Minor planets" /> in September 2006 the Caltech team submitted formal names from [[Hawaiian mythology]] to the IAU for both (136108) 2003&nbsp;EL<sub>61</sub> and its moons, in order "to pay homage to the place where the satellites were discovered".<ref name="mike" /> The names were proposed by [[David L. Rabinowitz|David Rabinowitz]] of the Caltech team.<ref name="iau" /> ''[[Haumea (mythology)|Haumea]]'' is the matron goddess of the island of [[Hawaii (island)|Hawaiʻi]], where the [[Mauna Kea Observatory]] is located. In addition, she is identified with [[Papahānaumoku|Papa]], the goddess of the earth and wife of [[Wākea]] (space),<ref name="craig" /> which, at the time, seemed appropriate because Haumea was 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.<ref name="iaunews" /><ref name="BrownBarkume2007" /> Lastly, Haumea is the goddess of fertility and childbirth, with many children who sprang from different parts of her body;<ref name="craig" /> this corresponds to the swarm of icy bodies thought to have broken off the main body during an ancient collision.<ref name="BrownBarkume2007" /> The two known moons, also believed to have formed in this manner,<ref name="BrownBarkume2007" /> are thus named after two of Haumea's daughters, [[Hiʻiaka]] and [[Nāmaka]].<ref name="iaunews" />

The proposal by the Ortiz team, Ataecina, did not meet IAU naming requirements, because the names of [[chthonic]] deities were reserved for stably [[resonant trans-Neptunian object]]s such as [[plutino]]s that resonate 3:2 with Neptune, whereas Haumea was in an intermittent 7:12 resonance and so by some definitions was not a resonant body. The naming criteria would be clarified in late 2019, when the IAU decided that chthonic figures were to be used specifically for plutinos. ''(See [[Ataecina#Dwarf planet|Ataecina §&thinsp;Dwarf planet]].)''

A [[planetary symbol]] for Haumea, {{angbr|[[File:Haumea symbol (fixed width).svg|16px|🝻]]}}, is included in [[Unicode]] at U+1F77B.<ref>{{Cite web |url=https://www.unicode.org/alloc/Pipeline.html |title=Proposed New Characters: The Pipeline |access-date=2022-01-29 |archive-date=2022-01-29 |archive-url=https://web.archive.org/web/20220129110620/https://www.unicode.org/alloc/Pipeline.html |url-status=live }}</ref> Planetary symbols are no longer much used in astronomy, and 🝻 is mostly used by astrologers,<ref name=miller>{{cite web|url=https://www.unicode.org/L2/L2021/21224-dwarf-planet-syms.pdf|title=Unicode request for dwarf-planet symbols|last=Miller|first=Kirk|date=26 October 2021|website=unicode.org|access-date=6 August 2022|archive-date=23 March 2022|archive-url=https://web.archive.org/web/20220323174107/https://www.unicode.org/L2/L2021/21224-dwarf-planet-syms.pdf|url-status=live}}</ref> but has also been used by NASA.<ref>{{cite web |url= https://www.jpl.nasa.gov/infographics/what-is-a-dwarf-planet |author= JPL/NASA |date= 22 April 2015 |website= Jet Propulsion Laboratory |title= What is a Dwarf Planet? |access-date= 2021-09-24 |archive-date= 2021-01-19 |archive-url= https://web.archive.org/web/20210119181743/https://www.jpl.nasa.gov/infographics/what-is-a-dwarf-planet |url-status= live }}</ref> The symbol was designed by Denis Moskowitz, a software engineer in Massachusetts; it combines and simplifies Hawaiian petroglyphs meaning 'woman' and 'childbirth'.<ref name=anderson>{{cite web |url=http://blog.unicode.org/2022/05/out-of-this-world-new-astronomy-symbols.html |title=Out of this World: New Astronomy Symbols Approved for the Unicode Standard |last=Anderson |first=Deborah |date=4 May 2022 |website=unicode.org |publisher=The Unicode Consortium |access-date=6 August 2022 |archive-date=6 August 2022 |archive-url=https://web.archive.org/web/20220806075352/http://blog.unicode.org/2022/05/out-of-this-world-new-astronomy-symbols.html |url-status=live }}</ref>

== Orbit ==
[[File:Quaoar Haumea Makemake orbits 2018.png|left|upright=1.5|thumb|Haumea's orbit outside of Neptune is similar to [[Makemake]]'s. The positions are as of January 1, 2018.]]
Haumea has an [[orbital period]] of 284 Earth years, a [[perihelion]] of 35&nbsp;[[Astronomical Units|AU]], and an [[orbital inclination]] of 28°.<ref name="jpldata" /> It passed [[aphelion]] in early 1992, and is currently more than 50&nbsp;AU from the Sun.<ref name="AstDys" /> It will come to perihelion in 2133.<ref name="perihelion" /> Haumea's orbit has a slightly greater [[orbital eccentricity|eccentricity]] than that of the other members of [[Haumea family|its collisional family]]. This is thought to be due to Haumea's weak 7:12 orbital resonance with Neptune gradually modifying its initial orbit over the course of a billion years,<ref name="BrownBarkume2007" /><ref name="largest" /> through the [[Kozai mechanism|Kozai effect]], which allows the exchange of an orbit's inclination for increased eccentricity.<ref name="BrownBarkume2007" /><ref name="Nesvorny2001" /><ref name="Kuchner2002" />

With a [[visual magnitude]] of 17.3,<ref name="AstDys" /> Haumea is the [[List of the brightest KBOs|third-brightest object]] in the Kuiper belt after Pluto and {{dp|Makemake}}, and easily observable with a large amateur telescope.<ref name="Rabinowitz2005" /> However, because the planets and most [[small Solar System bodies]] share a [[invariable plane|common orbital alignment]] from their [[formation and evolution of the Solar System|formation]] in the [[protoplanetary disk|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]].<ref name="TrujilloBrown2003" /> 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 motion]]s across the sky.<ref name="Brown2004" /><ref name="Schwamb2008" /> These surveys eventually covered the location of Haumea, with its high orbital inclination and current position far from the ecliptic.

=== Possible resonance with Neptune ===
{{multiple image |direction=vertical |align=right |total_width=300
 |image1=Haumea.GIF |caption1=The [[libration]] of Haumea's nominal orbit in a [[rotating frame]], with [[Neptune]] stationary (see [[2 Pallas#Near resonances|2 Pallas]] for an example of non-librating)
 |image2=Haumea resonant angle.png |caption2=The [[Resonant trans-Neptunian object#Definition|libration angle <small><math>\phi</math></small>]] of Haumea's weak 7:12 resonance with Neptune, <small><math>\phi = \rm 12\cdot\lambda - \rm 7\cdot\lambda_{\rm N} - \rm 5\cdot\varpi - \rm 1\cdot\Omega</math></small>, over the next 5 million years
}}

Haumea is thought to be in an intermittent 7:12 [[Resonant trans-Neptunian object|orbital resonance with Neptune]].<ref name="BrownBarkume2007" /> Its [[ascending node]] Ω precesses with a period of about 4.6 million years, and the resonance is broken twice per precession cycle, or every 2.3 million years, only to return a hundred thousand years or so later.<ref name="Buie"/> As this is not a simple resonance, [[Marc Buie]] qualifies it as non-resonant.<ref>{{Cite web|title=Orbit and Astrometry for 136108|url=https://www.boulder.swri.edu/~buie/kbo/astrom/136108.html|access-date=2020-07-14|website=www.boulder.swri.edu|archive-date=2020-07-13|archive-url=https://web.archive.org/web/20200713100758/https://www.boulder.swri.edu/~buie/kbo/astrom/136108.html|url-status=live}}</ref>
{{clear|left}}

== Rotation ==
Haumea displays large fluctuations in brightness over a period of 3.9 hours, which can only be explained by a rotational period of this length.<ref name="AFP2009" /> This is faster than any other known equilibrium body in the [[Solar System]], and indeed faster than any other known body larger than 100&nbsp;km in diameter.<ref name="Rabinowitz2005" /> While most rotating bodies in equilibrium are flattened into [[oblate spheroid]]s, Haumea rotates so quickly that it is distorted into a triaxial [[ellipsoid]]. If Haumea were to rotate much more rapidly, it would distort itself into a dumbbell shape and split in two.<ref name="iau" /> This rapid rotation is thought to have been caused by the impact that created its satellites and collisional family.<ref name="BrownBarkume2007" />

The plane of Haumea's [[equatorial bulge|equator]] is oriented nearly edge-on from Earth at present and is also slightly offset to the orbital planes of its [[#Ring|ring]] and its outermost moon [[Hiʻiaka (moon)|Hiʻiaka]]. Although initially assumed to be coplanar to Hiʻiaka's orbital plane by Ragozzine and Brown in 2009, their models of the collisional formation of Haumea's satellites consistently suggested Haumea's equatorial plane to be at least aligned with Hiʻiaka's orbital plane by approximately 1°.<ref name="RagozzineBrown2009" /> This was supported with observations of a [[stellar occultation]] by Haumea in 2017, which revealed the presence of a ring approximately coincident with the plane of Hiʻiaka's orbit and Haumea's equator.<ref name="Ortiz2017" /> A mathematical analysis of the occultation data by Kondratyev and Kornoukhov in 2018 placed constraints on the relative inclination angles of Haumea's equator to the orbital planes of its ring and Hiʻiaka, which were found to be inclined {{val|3.2|1.4|u=deg}} and {{val|2.0|1.0|u=deg}} relative to Haumea's equator, respectively.<ref name="Kondratyev2018"/>

== Physical characteristics ==
=== Size, shape, and composition ===

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 [[Infrared|thermal emission]] to be measured, which has given an approximate value for its albedo and thus its size.<ref name="spitzer"/> However, the calculation of its dimensions is complicated by its rapid rotation. The [[Rigid body dynamics|rotational physics]] of [[plasticity (physics)|deformable bodies]] predicts that over as little as a hundred days,<ref name="Rabinowitz2005" /> a body rotating as rapidly as Haumea will have been distorted into the [[Hydrostatic equilibrium|equilibrium form]] of a [[ellipsoid#Dynamical properties|triaxial 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 ends view as seen from Earth.<ref name="Rabinowitz2005"/>

The rotation and amplitude of Haumea's [[Light curve#Planetology|light curve]] were argued to place strong constraints on its composition. If Haumea were in [[hydrostatic equilibrium]] and had a low [[density]] like Pluto, with a thick mantle of [[Volatile (astrogeology)|ice]] over a small [[silicate|rocky]] core, its rapid rotation would have elongated it to a greater extent than the fluctuations in its brightness allow. Such considerations constrained its density to a range of 2.6–3.3&nbsp;g/cm<sup>3</sup>.<ref name="Lockwood2014" /><ref name="Rabinowitz2005" /> By comparison, the Moon, which is rocky, has a density of 3.3&nbsp;g/cm<sup>3</sup>, whereas Pluto, which is typical of icy objects in the Kuiper belt, has a density of 1.86&nbsp;g/cm<sup>3</sup>. Haumea's possible high density covered the values for [[silicate minerals]] such as [[olivine]] and [[pyroxene]], which make up many of the [[Planetary differentiation|rocky objects]] in the Solar System. This also suggested that the bulk of Haumea was 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.<ref name="BrownBarkume2007" />

Because Haumea has moons, the mass of the system can be calculated from their orbits using [[Kepler's laws of planetary motion#Third law of Kepler|Kepler's third law]]. The result is {{Val|4.2e21|u=kg}}, 28% the mass of the Plutonian system and 6% that of the [[Moon]]. Nearly all of this mass is in Haumea.<ref name="RagozzineBrown2009" /><ref name="Brown2005-AJL632" />
Several ellipsoid-model calculations of Haumea's dimensions have been made. The first model produced after Haumea's discovery was calculated from [[Observatory#Ground-based observatories|ground-based]] observations of Haumea's [[light curve]] at [[visible spectrum|optical]] wavelengths: it provided a total length of 1,960 to 2,500&nbsp;km and a [[visible spectrum|visual]] [[Albedo#Astronomical albedo|albedo]] (p<sub>v</sub>) greater than 0.6.<ref name="Rabinowitz2005" /> The most likely shape is a triaxial ellipsoid with approximate dimensions of 2,000 × 1,500 × 1,000&nbsp;km, with an albedo of 0.71.<ref name="Rabinowitz2005" /> Observations by the [[Spitzer Space Telescope]] gave a diameter of {{val|1150|+250|-100|u=km|fmt=commas}} and an albedo of {{val|0.84|+0.1|-0.2}}, from [[Photometry (astronomy)|photometry]] at [[infrared]] wavelengths of 70 μm.<ref name="spitzer" /> Subsequent light-curve analyses have suggested an equivalent circular diameter of 1,450&nbsp;km.<ref name="Lacerda2007" /> 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&nbsp;km.<ref name="Lellouch2010" /> These independent size estimates overlap at an average [[geometric mean]] diameter of roughly 1,400&nbsp;km. In 2013 the Herschel Space Telescope measured Haumea's equivalent circular diameter to be roughly {{val|1240|+69|-58|u=km|fmt=commas}}.<ref name="TNOsCool8" />

{{multiple image |direction=vertical |align=right |total_width=225
 |image1=Haumea.svg |caption1=The calculated ellipsoid shape of Haumea, 1,960×1,518×996&nbsp;km (assuming an [[albedo]] of 0.73). At the left are the minimum and maximum equatorial silhouettes (1,960×996 and 1,518×996&nbsp;km); at the right is the view from the [[geographical pole|pole]] (1,960×1,518&nbsp;km).
 |image2=Haumea Rotation.gif |caption2=Haumea's rapid rotation (of just under 4 hours) elongated it into a [[Jacobi ellipsoid|triaxial ellipsoid]] shape. Haumea exhibits distinguishable variations in colour as it rotates, indicative of a dark red spot on its surface as depicted here.
}}

However the observations of a [[asteroid occultation|stellar occultation]] in January 2017 cast a doubt on all those conclusions. The measured shape of Haumea, while elongated as presumed before, appeared to have significantly larger dimensions{{Snd}} according to the data obtained from the occultation Haumea is approximately the diameter of Pluto along its longest axis and about half that at its poles.<ref name="Ortiz2017" /> The resulting density calculated from the observed shape of Haumea was about {{val|1.8|u=g/cm3}}{{Snd}} more in line with densities of other large TNOs. This resulting shape appeared to be inconsistent with a homogenous body in hydrostatic equilibrium,<ref name="Ortiz2017"/> though Haumea appears to be one of the largest trans-Neptunian objects discovered nonetheless,<ref name="spitzer" /> smaller than {{dp|Eris}}, {{dp|Pluto}}, similar to {{dp|Makemake}}, and possibly {{dp|Gonggong}}, and larger than {{dp|Sedna}}, {{dp|Quaoar}}, and {{dp|Orcus}}.

A 2019 study attempted to resolve the conflicting measurements of Haumea's shape and density using [[Numerical modeling (geology)|numerical modeling]] of Haumea as a differentiated body. It found that dimensions of ≈ 2,100 × 1,680 × 1,074&nbsp;km (modeling the long axis at intervals of 25&nbsp;km) were a best-fit match to the observed shape of Haumea during the 2017 occultation, while also being consistent with both surface and core scalene ellipsoid shapes in hydrostatic equilibrium.<ref name="Dunham2019" /> The revised solution for Haumea's shape implies that it has a core of approximately 1,626 × 1,446 × 940&nbsp;km, with a relatively high density of ≈ {{val|2.68|u=g/cm3}}, indicative of a composition largely of hydrated silicates such as [[kaolinite]]. The core is surrounded by an icy mantle that ranges in thickness from about 70&nbsp;km at the poles to 170&nbsp;km along its longest axis, comprising up to 17% of Haumea's mass. Haumea's mean density is estimated at ≈ {{val|2.018|u=g/cm3}}, with an albedo of ≈ 0.66.<ref name="Dunham2019" />

=== Surface ===
In 2005, the [[Gemini Observatory|Gemini]] and [[Keck Observatory|Keck]] telescopes obtained [[spectrum|spectra]] of Haumea which showed strong crystalline [[ice|water ice]] features similar to the surface of Pluto's moon [[Charon (moon)|Charon]].<ref name="Trujillo 2006" /> This is peculiar, because crystalline ice forms at temperatures above 110&nbsp;K, whereas Haumea's surface temperature is below 50&nbsp;K, a temperature at which [[amorphous ice]] is formed.<ref name="Trujillo 2006" /> In addition, the structure of crystalline ice is unstable under the constant rain of [[cosmic ray]]s and energetic particles from the Sun that strike trans-Neptunian objects.<ref name="Trujillo 2006" /> The timescale for the crystalline ice to revert to amorphous ice under this bombardment is on the order of ten million years,<ref name="Gemini-Charon ice machine" /> yet trans-Neptunian objects have been in their present cold-temperature locations for timescales of billions of years.<ref name="largest" />

Radiation damage should also redden and darken the surface of trans-Neptunian objects where the common surface materials of [[organic molecule|organic]] ices and [[tholin|tholin-like]] compounds are present, as is the case with Pluto. Therefore, the spectra and [[colour index|colour]] suggest Haumea and its family members have undergone recent resurfacing that produced fresh ice. However, no plausible resurfacing mechanism has been suggested.<ref name="Rabinowitz2008" />

Haumea is as bright as snow, with an albedo in the range of 0.6–0.8, consistent with crystalline ice.<ref name="Rabinowitz2005" /> Other large TNOs such as {{dp|Eris}} appear to have albedos as high or higher.<ref name="Brown2006xsize" /> Best-fit modeling 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 [[Silicate minerals#Phyllosilicates|phyllosilicate clays]].<ref name="Trujillo 2006" /> Inorganic cyanide salts such as copper potassium cyanide may also be present.<ref name="Trujillo 2006" />

However, further studies of the visible and near infrared spectra suggest a homogeneous 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.<ref name="Pinilla-Alonso2009" />
The absence of measurable [[methane]] in the spectra of Haumea is consistent with a warm [[Impact crater|collisional history]] that would have removed such [[Volatile (astrogeology)|volatiles]],<ref name="Trujillo 2006" /> in contrast to {{dp|Makemake}}.<ref name="Tegler07" />

In addition to the large fluctuations in Haumea's light curve due to the body's shape, which affect all [[Colour index|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.<ref name="hour" /><ref name="Lacerda2009" /> 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.<ref name="AFP2009" /><ref name="SpaceCom-Haumea dark spot" /> Thus Haumea may have a mottled surface reminiscent of Pluto, if not as extreme.

== Ring ==
[[File:Haumea_rotation_with_ring.gif|thumb|Haumea's 3.9155-hour rotation within its discovered ring]]
A stellar occultation observed on 21 January 2017, and described in an October 2017 ''[[Nature (journal)|Nature]]'' article indicated the presence of a [[ring system|ring]] around Haumea. This represents the first ring system discovered for a TNO.<ref name="Ortiz2017"/><ref>[http://www.skyandtelescope.com/astronomy-news/dwarf-planet-haumea-has-a-ring Surprise! Dwarf Planet Haumea Has a Ring] {{Webarchive|url=https://web.archive.org/web/20171022141552/http://www.skyandtelescope.com/astronomy-news/dwarf-planet-haumea-has-a-ring |date=2017-10-22 }}, Sky and Telescope, 13 October 2017.</ref> The ring has a radius of about 2,287&nbsp;km, a width of ~70&nbsp;km and an opacity of 0.5. It is well within Haumea's [[Roche limit]], which would be at a radius of about 4,400&nbsp;km if it were spherical (being nonspherical pushes the limit out farther).<ref name="Ortiz2017" />

The ring plane is inclined {{val|3.2|1.4|u=deg}} with respect to Haumea's equatorial plane and approximately coincides with the orbital plane of its larger, outer moon Hiʻiaka.<ref name="Ortiz2017" /><ref name="Kondratyev2020" /> The ring is also close to the 1:3 [[orbital resonance|orbit-spin resonance]] with Haumea's rotation (which is at a radius of 2,285 ± 8&nbsp;km from Haumea's center). The ring is estimated to contribute 5% to the total brightness of Haumea.<ref name="Ortiz2017" />

In a study about the [[orbital dynamics|dynamics]] of ring particles published in 2019, Othon Cabo Winter and colleagues have shown that the 1:3 resonance with Haumea's rotation is [[Separatrix (mathematics)|dynamically unstable]], but that there is a stable region in the [[phase space]] consistent with the location of Haumea's ring. This indicates that the ring particles originate on circular, periodic orbits that are close to, but not inside, the resonance.<ref name="Winter2019">{{cite journal|title= On the location of the ring around the dwarf planet Haumea|first1= O. C.|last1= Winter|first2= G.|last2= Borderes-Motta|first3= T.|last3= Ribeiro|arxiv= 1902.03363|year= 2019|volume= 484|issue= 3|journal= Monthly Notices of the Royal Astronomical Society|pages= 3765–3771|doi= 10.1093/mnras/stz246|doi-access= free|s2cid= 119260748}}</ref>

== Satellites ==
{{main|Moons of Haumea}}
[[File:Haumea-moons-hubble.gif|thumb|Haumea and its orbiting moons, imaged by [[Hubble Space Telescope|Hubble]] in 2008. [[Hiʻiaka (moon)|Hiʻiaka]] is the brighter, outermost moon, while [[Namaka (moon)|Namaka]] is the fainter, inner moon.]]

Two small [[natural satellite|satellites]] have been discovered orbiting Haumea, (136108) Haumea I '''[[Hiʻiaka (moon)|Hiʻiaka]]''' and (136108) Haumea II '''[[Namaka (moon)|Namaka]]'''.<ref name="usgs" /> Darin Ragozzine and Michael Brown discovered both in 2005, through observations of Haumea using the [[W. M. Keck Observatory]].

Hiʻiaka, at first nicknamed "[[Rudolph the Red-Nosed Reindeer|Rudolph]]" by the Caltech team,<ref name="Chang2007-Iceball" /> was discovered 26 January 2005.<ref name="Brown2005-AJL632" /> It is the outer and, at roughly 310&nbsp;km in diameter, the larger and brighter of the two, and orbits Haumea in a nearly circular path every 49&nbsp;days.<ref name="Brown2006-discovery" /> Strong absorption features at 1.5 and 2 [[micrometre]]s in the [[infrared]] spectrum are consistent with nearly pure crystalline water ice covering much of the surface.<ref name="Barkume2006" /> 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.<ref name="largest" />

Namaka, the smaller, inner satellite of Haumea, was discovered on 30 June 2005,<ref name="IAUC_8636" /> and nicknamed "[[Blitzen the Reindeer|Blitzen]]". It is a tenth the mass of Hiʻiaka, orbits Haumea in 18 days in a highly elliptical, [[Osculating orbit|non-Keplerian]] orbit, and {{as of|2008|lc=on}} is inclined 13° from the larger moon, which [[Perturbation (astronomy)|perturbs]] its orbit.<ref name="RagozzineDPS08" />
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 acceleration|tidal effects]]. A relatively recent passage by a 3:1 resonance with Hiʻiaka might explain the current excited orbits of the Haumean moons.<ref name="Brown2009" />

From around 2008 to 2011,<ref>{{cite journal |last1=Dumas |first1=C. |last2=Carry |first2=B. |first3=D. |last3=Hestroffer |first4=F. |last4=Merlin |date=2011 |title=High-contrast observations of (136108) Haumea |url=https://www.aanda.org/articles/aa/full_html/2011/04/aa15011-10/aa15011-10.html |journal=Astronomy & Astrophysics |volume=528 |issue= |pages= A105|doi=10.1051/0004-6361/201015011 |access-date=24 August 2024|arxiv=1101.2102 }}</ref> the orbits of the Haumean moons appeared almost exactly edge-on from Earth, with Namaka periodically [[occultation|occulting]] Haumea.<ref name="IAU8949" /> Observation of such transits would have provided precise information on the size and shape of Haumea and its moons,<ref name="events09" /> as happened in [[Solar eclipses on Pluto|the late 1980s with Pluto and Charon.]]<ref name="McFadden2007" /> The tiny change in brightness of the system during these occultations would have required at least a [[Optical telescope#Optical Research telescopes|medium]]-[[aperture]] [[List of optical telescopes|professional telescope]] for detection.<ref name="events09" /><ref name="FabryckyDPS08" /> Hiʻiaka last occulted Haumea in 1999, a few years before discovery, and will not do so again for some 130 years.<ref name="shadows" /> However, in a situation unique among [[regular moon|regular satellites]], Namaka's orbit was being greatly [[Apsidal precession|torqued]] by Hiʻiaka, which preserved the viewing angle of Namaka–Haumea transits for several more years.<ref name="RagozzineDPS08" /><ref name="events09" /><ref name="FabryckyDPS08" /> One occultation event was observed on 19 June 2009, from the [[Pico dos Dias Observatory]] in Brazil.<ref>{{cite journal |last1=Bortoletto |first1=A. |last2=Saito |first2=R. K. |date=2010 |title=Observing mutual events of the trans-Neptunian object Haumea and Namaka from Brazil |url=https://articles.adsabs.harvard.edu//full/2010IAUS..269..189B/0000189.000.html |journal=Proceedings of the International Astronomical Union, IAU Symposium |volume=269 |issue= |pages=189–192 |bibcode=2010IAUS..269..189B |doi= 10.1017/S1743921310007404|access-date=24 August 2024}}</ref><!--article text says 16th but figure says 19th. Probably 19th, since Mike Brown's site confirms occultation was on the 19th-->

{| class="wikitable"
|+Haumean system
!Name
!Diameter (km)<ref name=":0">{{Cite web|title=Moons of the Dwarf Planet Haumea: Hi'iaka and Namaka - Windows to The Universe|url=https://www.windows2universe.org/?page=%2Four_solar_system%2Fdwarf_planets%2Fhaumea_moons.html|website=Windows To The Universe|access-date=2021-06-08|archive-date=2021-06-28|archive-url=https://web.archive.org/web/20210628060001/https://www.windows2universe.org/?page=%2Four_solar_system%2Fdwarf_planets%2Fhaumea_moons.html|url-status=live}}</ref><ref>{{Cite journal|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.|date=October 2017|title=The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation|url=http://www.nature.com/articles/nature24051|journal=Nature|language=en|volume=550|issue=7675|pages=219–223|doi=10.1038/nature24051|pmid=29022593|issn=0028-0836|arxiv=2006.03113|bibcode=2017Natur.550..219O|s2cid=205260767|access-date=2021-07-08|archive-date=2022-06-23|archive-url=https://web.archive.org/web/20220623072708/https://www.nature.com/articles/nature24051|url-status=live}}</ref>
!Semi-major axis (km)<ref name=":1">{{Cite journal|last1=Ragozzine|first1=D.|last2=Brown|first2=M. E.|title=Orbits and Masses of the Satellites of the Dwarf Planet Haumea (2003 El61)|date=2009-06-01|url=https://iopscience.iop.org/article/10.1088/0004-6256/137/6/4766|journal=The Astronomical Journal|volume=137|issue=6|pages=4766–4776|doi=10.1088/0004-6256/137/6/4766|arxiv=0903.4213|bibcode=2009AJ....137.4766R|s2cid=15310444|issn=0004-6256|access-date=2021-07-08|archive-date=2021-05-09|archive-url=https://web.archive.org/web/20210509160155/https://iopscience.iop.org/article/10.1088/0004-6256/137/6/4766|url-status=live}}</ref>
!Mass (kg)<ref name=":1" />
!Discovery date<ref name=":0" /><ref name=":2">{{Cite web|title=In Depth {{!}} Haumea|url=https://solarsystem.nasa.gov/planets/dwarf-planets/haumea/in-depth/|access-date=July 8, 2021|website=NASA Solar System Exploration|archive-date=June 29, 2021|archive-url=https://web.archive.org/web/20210629203746/https://solarsystem.nasa.gov/planets/dwarf-planets/haumea/in-depth/|url-status=live}}</ref>
|-
|Haumea
|2 322 × 1,704 × 1,026
|
|(4.006 ± 0.040) × 10<sup>21</sup>
|7 March 2003<ref name=":2" />
|-
|[[Hiʻiaka (moon)|Hiʻiaka]]
|{{Sort|0310|≈ 310}}
|49 880
|(1.79 ± 0.11) x 10<sup>19</sup>
|26 January 2005
|-
|[[Namaka (moon)|Namaka]]
|{{Sort|0170|≈ 170}}
|25 657
|(1.79 ± 1.48) x 10<sup>18</sup>
|30 June 2005
|}

== Collisional family ==
{{main|Haumea family}}

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.<ref name="BrownBarkume2007" /> This family is the first to be identified among TNOs and includes—beside Haumea and its moons—{{mpl|(55636) 2002 TX|300}} (≈364&nbsp;km), {{mpl|(24835) 1995 SM|55}} (≈174&nbsp;km), {{mpl|(19308) 1996 TO|66}} (≈200&nbsp;km), {{mpl|(120178) 2003 OP|32}} (≈230&nbsp;km), and {{mpl|(145453) 2005 RR|43}} (≈252&nbsp;km).<ref name="candidate" /> Brown and colleagues proposed that the family were a direct product of the impact that removed Haumea's ice mantle,<ref name="BrownBarkume2007" /> 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.<ref name="SchlichtingSari2009" /> 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.<ref name="SchlichtingSari2009" />

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.<ref name="disc" /> The family could not have formed in the denser primordial Kuiper belt because such a close-knit group would have been disrupted by [[Neptune#Formation and migration|Neptune's migration]] into the belt—the believed cause of the belt's current low density.<ref name="disc" /> 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.<ref name="disc" />

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.<ref name="candidate" />

== Exploration ==
[[File:Haumea New Horizons.gif|thumb|Haumea imaged by the ''[[New Horizons (spacecraft)|New Horizons]]'' spacecraft on 6 October 2007]]
Haumea was observed from afar by the ''[[New Horizons]]'' spacecraft in October 2007, January 2017, and May 2020, from distances of 49&nbsp;AU, 59&nbsp;AU, and 63&nbsp;AU, respectively.<ref name="Verbiscer2022"/> The spacecraft's outbound trajectory permitted observations of Haumea at high [[phase angle (astronomy)|phase angles]] that are otherwise unobtainable from Earth, enabling the determination of the light scattering properties and [[phase curve (astronomy)|phase curve]] behavior of Haumea's surface.<ref name="Verbiscer2022"/>

Joel Poncy and colleagues calculated that a flyby mission to Haumea could take 14.25 years using a gravity assist from Jupiter, based on a launch date of 25 September 2025. Haumea would be 48.18&nbsp;AU from the Sun when the spacecraft arrives. A flight time of 16.45 years can be achieved with launch dates on 1 November 2026, 23 September 2037, and 29 October 2038.<ref name=McGranaghan>{{cite journal|author1=McGranaghan, R. |author2=Sagan, B. |author3=Dove, G. |author4=Tullos, A. |author5=Lyne, J. E. |author6=Emery, J. P. |date=2011|title=A Survey of Mission Opportunities to Trans-Neptunian Objects|journal= Journal of the British Interplanetary Society|volume=64|pages=296–303|bibcode=2011JBIS...64..296M}}</ref>
Haumea could become a target for an exploration mission,<ref name="Poncy">{{cite journal | last1 = Poncy | first1 = Joel | last2 = Fontdecaba Baiga | first2 = Jordi | last3 = Feresinb | first3 = Fred | last4 = Martinota | first4 = Vincent | year = 2011 | title = A preliminary assessment of an orbiter in the Haumean system: How quickly can a planetary orbiter reach such a distant target? | journal = Acta Astronautica | volume = 68 | issue = 5–6| pages = 622–628 | doi=10.1016/j.actaastro.2010.04.011|bibcode = 2011AcAau..68..622P }}</ref> and an example of this work is a preliminary study on a probe to Haumea and its moons (at 35–51&nbsp;AU).<ref>Paul Gilster: [http://www.centauri-dreams.org/?p=8680 ''Fast Orbiter to Haumea''] {{webarchive|url=https://web.archive.org/web/20150923202157/http://www.centauri-dreams.org/?p=8680 |date=2015-09-23 }}. Centauri Dreams—The News of the Tau Zero Foundation. 14 July 2009, retrieved 15 January 2011</ref> Probe mass, power source, and propulsion systems are key technology areas for this type of mission.<ref name="Poncy" />

== See also ==
* [[Astronomical naming conventions]]
* [[Clearing the neighbourhood]]
* [[International Astronomical Union]]
* [[Planets beyond Neptune]]
* [[List of Solar System objects most distant from the Sun]]

== Notes ==
{{reflist|group=nb}}

== References ==
{{reflist
| colwidth = 30em
| refs =

<ref name="Lockwood2014">
{{cite journal
| author = Alexandra C. Lockwood
| author2 = Michael E. Brown
| author3 = John Stansberry
| date = 2014
| title = The size and shape of the oblong dwarf planet Haumea
| journal = Earth, Moon, and Planets
| arxiv = 1402.4456v1
| doi = 10.1007/s11038-014-9430-1
| volume = 111
| issue = 3–4
| pages = 127–137
| bibcode = 2014EM&P..111..127L
| s2cid = 18646829
}}
</ref>

<ref name="K10H75">{{cite web
| title = MPEC 2010-H75: Distant Minor Planets (2010 May 14.0 TT)
| date = 2010-04-10
| publisher = Minor Planet Center
| url = https://minorplanetcenter.net/mpec/K10/K10H75.html
| access-date = 2010-07-02
| archive-date = 2014-07-16
| archive-url = https://web.archive.org/web/20140716082845/http://www.minorplanetcenter.net/mpec/K10/K10H75.html
| url-status = live
}}</ref>

<ref name="Buie">
{{cite web
 |author      = Marc W. Buie
 |author-link = Marc W. Buie
 |date        = 2008-06-25
 |title       = Orbit Fit and Astrometric record for 136108
 |publisher   = Southwest Research Institute (Space Science Department)
 |url         = http://www.boulder.swri.edu/~buie/kbo/astrom/136108.html
 |access-date  = 2008-10-02
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20110518005546/http://www.boulder.swri.edu/~buie/kbo/astrom/136108.html
 |archive-date = 2011-05-18
}}
</ref>

<ref name="candidate">
{{cite journal
| author1 = Ragozzine, D.
| date = 2007
| title = Candidate Members and Age Estimate of the Family of Kuiper Belt Object 2003&nbsp;EL<sub>61</sub>
| journal = [[Astronomical Journal]]
| volume = 134
| issue = 6
| pages = 2160–2167
| doi = 10.1086/522334
| bibcode = 2007AJ....134.2160R
| arxiv = 0709.0328
| author2 = Brown, M. E.
| s2cid = 8387493
}}
</ref>

<ref name="jpldata">{{cite web
 |type         = 2019-08-26 last obs
 |title        = Jet Propulsion Laboratory Small-Body Database Browser: 136108 Haumea (2003&nbsp;EL<sub>61</sub>)
 |publisher    = NASA's Jet Propulsion Laboratory
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<ref name="MPC-object">{{cite web
 |title        = (136108) Haumea = 2003 EL61
 |work         = [[Minor Planet Center]]
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{{cite journal
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{{cite journal
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<ref name="AstDys">
{{cite web
 |title       = AstDys (136108) Haumea Ephemerides
 |publisher   = Department of Mathematics, University of Pisa, Italy
 |url         = https://newton.spacedys.com/astdys/index.php?pc=1.1.3.0&n=Haumea
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<ref name="Horizons">{{cite web
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<ref name="Trujillo 2006">
{{cite journal
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| author2 = Michael E. Brown
| author3 = Kristina Barkume
| author4 = Emily Shaller
| author5 = David L. Rabinowitz
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<ref name="usgs">
{{cite news
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<ref name="iau">{{cite news
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<ref name="trail">
{{cite web
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<ref name="Sanz">
{{cite web
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<ref name="ortiz1">
{{cite news
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<ref name="marsden">
{{cite web
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<ref name="Santa2005">
{{cite web
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{{cite news
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<ref name="mike">
{{cite web
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<ref name="craig">{{cite book
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<ref name="iaunews">
{{cite web
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<ref name="AFP2009">
{{cite web
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{{cite web
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{{cite news
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| issue = 1
| pages = L45–L48
| doi = 10.1086/497641
| bibcode = 2005ApJ...632L..45B
| last2 = Bouchez
| first2 = A. H.
| last3 = Rabinowitz
| first3 = D.
| last4 = Sari
| first4 = R.
| last5 = Trujillo
| first5 = C. A.
| last6 = Van Dam
| first6 = M.
| last7 = Campbell
| first7 = R.
| last8 = Chin
| first8 = J.
| last9 = Hartman
| first9 = S.
| last10 = Johansson
| first10 = E.
| last11 = Lafon
| first11 = R.
| last12 = Le Mignant
| first12 = D.
| last13 = Stomski
| first13 = P.
| last14 = Summers
| first14 = D.
| last15 = Wizinowich
| first15 = P.
| s2cid = 119408563
| url = http://authors.library.caltech.edu/34486/1/1538-4357_632_1_L45.pdf
| access-date = 2018-11-04
| archive-date = 2017-12-02
| archive-url = https://web.archive.org/web/20171202123850/https://authors.library.caltech.edu/34486/1/1538-4357_632_1_L45.pdf
| url-status = live
}}</ref>

<ref name="Brown2006-discovery">
{{cite journal| doi = 10.1086/501524| last1 = Brown| first1 = M. E.| author-link = 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| arxiv = astro-ph/0510029| bibcode = 2006ApJ...639L..43B| s2cid = 2578831| url = http://web.gps.caltech.edu/~mbrown/papers/ps/gab.pdf| access-date = 2011-10-19| ref = {{sfnRef|Brown Van Dam et al.|2006}}| url-status = live| archive-url = https://web.archive.org/web/20131103094637/http://web.gps.caltech.edu/~mbrown/papers/ps/gab.pdf| archive-date = 2013-11-03}}
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{{cite journal
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| name-list-style = amp
| date = 2006
| title = Water Ice on the Satellite of Kuiper Belt Object 2003 EL<sub>61</sub>
| journal = [[Astrophysical Journal Letters]]
| volume = 640
| issue = 1
| pages = L87–L89
| doi = 10.1086/503159
| arxiv = astro-ph/0601534
| bibcode = 2006ApJ...640L..87B
| s2cid = 17831967
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<ref name="IAUC_8636">
{{cite web
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<ref name="RagozzineDPS08">
{{cite conference
| author1 = Ragozzine, D.
| title = Orbits and Masses of the 2003 EL61 Satellite System
| conference = AAS DPS conference 2008
| bibcode = 2008DPS....40.3607R
| author2 = Brown, M. E.
| author3 = Trujillo, C. A.
| author4 = Schaller, E. L.
| volume = 40
| date = 2008
| page = 462
| journal = Bulletin of the American Astronomical Society
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<ref name="Brown2009">
{{cite journal
| author1 = Ragozzine, D.
| author2 = Brown, M. E.
| date = 2009
| title = Orbits and Masses of the Satellites of the Dwarf Planet Haumea {{=}} 2003 EL<sub>61</sub>
| doi = 10.1088/0004-6256/137/6/4766
| journal = The Astronomical Journal
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<ref name="IAU8949">
{{cite web
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<ref name="events09">
{{cite web
 |title       = Mutual events of Haumea and Namaka
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<ref name="McFadden2007">
{{cite book
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| author2 = P. R. Weissman
| author3 = T. V. Johnson
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</ref>

<ref name="FabryckyDPS08">
{{cite conference
| author1 = Fabrycky, D. C. 
| title = Mutual Events of 2003 EL<sub>61</sub> and its Inner Satellite
| conference = AAS DPS conference 2008
| bibcode = 2008DPS....40.3608F
| author2 = Holman, M. J.
| author3 = Ragozzine, D.
| author4 = Brown, M. E.
| author5 = Lister, T. A.
| author6 = Terndrup, D. M.
| author7 = Djordjevic, J.
| author8 = Young, E. F.
| author9 = Young, L. A.
| last10 = Howell
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| volume = 40
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| journal = Bulletin of the American Astronomical Society
}}
</ref>

<ref name="shadows">
{{cite web
 |author      = M. Brown
 |date        = 18 May 2008
 |title       = Moon shadow Monday (fixed)
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}}
</ref>

<ref name="SchlichtingSari2009">
{{cite journal
| author1 = Schlichting, H. E.
| date = 2009
| title = The Creation of Haumea's Collisional Family
| doi = 10.1088/0004-637X/700/2/1242
| journal = The Astrophysical Journal
| volume = 700
| issue = 2
| pages = 1242–1246
| arxiv = 0906.3893
| bibcode = 2009ApJ...700.1242S
| author2 = Sari, R.
| s2cid = 19022987
}}
</ref>

<ref name="disc">
{{cite journal
| title = On a Scattered Disc Origin for the 2003&nbsp;EL<sub>61</sub> Collisional Family—an Example of the Importance of Collisions in the Dynamics of Small Bodies
| author1 = Levison, H. F.
| date = 2008
| journal = [[Astronomical Journal]]
| volume = 136
| issue = 3
| pages = 1079–1088
| doi = 10.1088/0004-6256/136/3/1079
| bibcode = 2008AJ....136.1079L
| arxiv = 0809.0553
| author2 = Morbidelli, A.
| author3 = Vokrouhlický, D.
| author4 = Bottke, W. F.
| s2cid = 10861444
}}
</ref>

<ref name="Ortiz2017">{{cite journal
| display-authors = etal
| 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.
| title = The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation
| url = http://www.astrosurf.com/sogorb/occultations/nature24051.pdf
| journal = Nature
| volume = 550
| issue = 7675
| year = 2017
| pages = 219–223
| doi = 10.1038/nature24051
| pmid = 29022593
| bibcode = 2017Natur.550..219O
| arxiv = 2006.03113
| hdl = 10045/70230
| s2cid = 205260767
| hdl-access = free
| access-date = 2020-08-19
| archive-date = 2020-11-07
| archive-url = https://web.archive.org/web/20201107052958/http://www.astrosurf.com/sogorb/occultations/nature24051.pdf
| url-status = live
}}</ref>

<ref name="Dunham2019">
{{cite journal
| title = Haumea's Shape, Composition, and Internal Structure
| author1 = Dunham, E. T.
| author2 = Desch, S. J.
| author3 = Probst, L.
| date = April 2019
| journal = The Astrophysical Journal
| volume = 877
| issue = 1
| page = 11
| doi = 10.3847/1538-4357/ab13b3
| bibcode = 2019ApJ...877...41D
| arxiv = 1904.00522
| s2cid = 90262114
| doi-access = free
}}
</ref>

<ref name="TNOsCool12">{{cite journal
  |title="TNOs are Cool": A survey of the trans-Neptunian region XII. Thermal light curves of Haumea, {{mp|2003 VS|2}} and {{mp|2003 AZ|84}} with Herschel/PACS
  |first1=P. |last1=Santos-Sanz
  |first2=E. |last2=Lellouch
  |first3=O. |last3=Groussin
  |first4=P. |last4=Lacerda
  |first5=T. G. |last5=Muller
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  |first7=C. |last7=Kiss
  |first8=E. |last8=Vilenius
  |first9=J. |last9=Stansberry
  |first10=R. |last10=Duffard
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  |doi=10.1051/0004-6361/201630354
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  |date=August 2017|s2cid=119489622 }}</ref>

<ref name="Kondratyev2018">
{{cite journal
| last1 = Kondratyev |first1 = B. P.
| last2 = Kornoukhov |first2 = V. S.
| title = Determination of the body of the dwarf planet Haumea from observations of a stellar occultation and photometry data
| journal = Monthly Notices of the Royal Astronomical Society
| volume = 478
| issue = 3
| date = August 2018
| pages = 3159–3176
| doi = 10.1093/mnras/sty1321
|doi-access = free
| bibcode = 2018MNRAS.478.3159K
}}</ref>

<ref name="Kondratyev2020">
{{cite journal
| last1 = Kondratyev |first1 = B. P.
| last2 = Kornoukhov |first2 = V. S.
| title = Secular Evolution of Rings around Rotating Triaxial Gravitating Bodies
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| volume = 64
| issue = 10
| date = October 2020
| pages = 870–875
| doi = 10.1134/S1063772920100030
| bibcode = 2020ARep...64..870K
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<ref name="Verbiscer2022">{{cite journal
  |display-authors = etal
  |first1 = Anne J. |last1 = Verbiscer
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  |first3 = Simon B. |last3 = Porter
  |first4 = Susan D. |last4 = Benecchi
  |first5 = J. J. |last5 = Kavelaars
  |first6 = Tod R. |last6 = Lauer
  |title      = The Diverse Shapes of Dwarf Planet and Large KBO Phase Curves Observed from New Horizons
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<ref name="perihelion">{{cite web
  |title = Horizons Batch for Haumea at perihelion around 1 June 2133
  |type = Perihelion occurs when rdot flips from negative to positive. The JPL SBDB generically (incorrectly) lists an unperturbed two-body perihelion date in 2132
  |url = https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%2720136108%27&START_TIME=%272133-05-25%27&STOP_TIME=%272133-06-14%27&STEP_SIZE=%273%20hours%27&QUANTITIES=%2719%27
  |work = [[JPL Horizons On-Line Ephemeris System|JPL Horizons]]
  |publisher = Jet Propulsion Laboratory
  |access-date = 13 September 2021
  |archive-date = 2021-09-13
  |archive-url = https://web.archive.org/web/20210913093519/https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Haumea%27&START_TIME=%272133-05-25%27&STOP_TIME=%272133-06-14%27&STEP_SIZE=%273%20hours%27&QUANTITIES=%2719%27
  |url-status = live
  }}</ref>

<ref name="coordstransform">{{cite web
 |title = Coordinate Transformation & Galactic Extinction Calculator
 |url = https://ned.ipac.caltech.edu/forms/calculator.html
 |work = NASA/IPAC Extragalactic Database
 |publisher = California Institute of Technology
 |access-date = 11 February 2023
 |archive-date = 22 January 2023
 |archive-url = https://web.archive.org/web/20230122012016/http://ned.ipac.caltech.edu/forms/calculator.html
 |url-status = live
 }} Equatorial → Ecliptic, J2000 for equinox and epoch. NOTE: When inputting equatorial coordinates, specify the units in the format "282.6d" instead of "282.6".</ref>

}} <!-- end of reflist -->

== External links ==
{{commons category|136108 Haumea}}
{{Wikinews|Kuiper Belt object to become comet in approx. 2 million years}}
* [http://www.johnstonsarchive.net/astro/astmoons/am-136108.html (136108) Haumea, Hiʻiaka, and Namaka] at Johnston's Archive.com (updated 21 September 2014)
* [[International Year of Astronomy|International Year of Astronomy 2009]] [http://365daysofastronomy.org/2009/03/31/march-31st/ podcast: Dwarf Planet Haumea (Darin Ragozzine)]
* [http://twitpic.com/59rbgj Haumea as seen on June 10, 2011] by Mike Brown using the {{convert|4.20|m|in|abbr=on}} [[William Herschel Telescope|WHT]] / [http://twitpic.com/5acp9q ~0:30–3:30 dip in the brightness of Haumea+Namaka comes when Namaka crosses Haumea] (Hiʻiaka, the outer moon, is blended in the images, but it rotates every 4.5 hr and adds a little variation)
* [https://imgur.com/DMlqRbx Animation of Haumea's intermittent 7:12 resonance with Neptune over the next 3.5 million years]

{{Haumea}}
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[[Category:Haumea (dwarf planet)| ]]
[[Category:Haumea family]]
[[Category:Trans-Neptunian objects|136108]]
[[Category:Discoveries by Michael E. Brown]]
[[Category:Discoveries by Chad Trujillo]]
[[Category:Discoveries by David L. Rabinowitz]]
[[Category:Named minor planets]]
[[Category:Planetary rings]]
[[Category:Objects observed by stellar occultation|136108]]
[[Category:Astronomical objects discovered in 2004|20041228]]
[[Category:Dwarf planets]]
[[Category:Solar System]]