Haumea

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Haumea
Artist's conception of Haumea,
with its moons, Hiʻiaka and Namaka
 
Discovery
Discovered byBrown et al.; Ortiz et al. (neither official)
Discovery date2004 December 28 (Brown et al.); 2005 July (Ortiz et al.)
Designations
Designation
(136108) Haumea
2003 EL61
dwarf planet, plutoid, TNO (cubewano)
Orbital characteristics
Epoch 2005-08-18 (JD 2 453 600.5)
Aphelion7 708 Gm (51.526 AU)
Perihelion5 260 Gm (35.164 AU)
6 484 Gm (43.335 AU)
Eccentricity0.188 74
104 234 d (285.4 a)
4.484 km/s
198.07°
Inclination28.19°
121.90°
239.51°
Known satellites2
Physical characteristics
Dimensions~1960 × 1518 × 996 km
(~1500 km)
1150 +250/-100 km[1]
Mass(4.2 ± 0.1)×1021 kg
Mean density
2.6–3.3 g/cm³
0.44 m/s²
0.84 km/s
0.163 14 ± 0.000 01 d
(3.915 4 ± 0.000 2 h)
Albedo0.7 ± 0.1
Temperature32 ± 3 K
Spectral type
?
17.3 (opposition)[2]
0.17[3]

Haumea (Template:Pron-en), formally designated (136108) Haumea, is a dwarf planet in the Kuiper belt, roughly one-third the mass of Pluto, discovered by Mike Brown's team at Caltech in the United States and J. L. Ortiz et al. of the Instituto de Astrofísica de Andalucía at Sierra Nevada Observatory in Spain (see Discovery controversy section). On September 17, 2008, it was classified as a dwarf planet by the IAU and named after the Hawaiian goddess of childbirth and fertility.

Haumea is considered exceptional among the known Classical Kuiper belt objects due to its extreme elongation; it is twice as long along its greatest equatorial diameter as it is wide at the poles.[citation needed] However, as its gravity is sufficient to maintain a rounded ellipsoidal shape, it meets the requirement for hydrostatic equilibrium used in the definition of dwarf planets. This elongation, along with Haumea's rapid rotation, two moons, high density, and high albedo due to crystalline water ice on the surface, are thought to be the results of a massive collision that left Haumea the largest member of a collisional family.

Name and classification

Haumea is officially classified as a dwarf planet, meaning that it is large enough to have reached a state of hydrostatic equilibrium, but has yet to clear its neighborhood of similar objects. Its designation as a dwarf planet and its orbital location also means it is classified as a plutoid.[4] Although it is not spherical, Haumea is considered a dwarf planet because it is in hydrostatic equilibrium: its ellipsoidal shape is due to its rapid rotation (in much the same way as a water balloon stretches out when tossed) and not due to insufficient self-gravity.[5]

Prior to being given the name Haumea, it had been assigned the temporary designation of (136108) 2003 EL61. In their own work, the Caltech team had used the nickname "Santa", which stems from its discovery on December 28, 2004, just after Christmas, using images from May 6, 2004. Following established IAU guidelines,[6] the object was formally named after a deity related to a creation myth. The Caltech team submitted formal names from Hawaiian mythology in September 2006 for (136108) 2003 EL61 and both of its satellites in order "to pay homage to the place where the satellites were discovered".[7]

On September 17, 2008, the International Astronomical Union classified (136108) 2003 EL61 as a dwarf planet and announced[5] that they had officially accepted the name "Haumea", after the Hawaiian goddess of childbirth and fertility, proposed by David Rabinowitz of the Brown team, with the moons named "Hiʻiaka" and "Namaka", after two of her daughters. The name was chosen in part to reflect the objects' manner of formation; according to myth, the children of Haumea sprang from different parts of her body. Similarly, moons of the dwarf planet Haumea are believed to have been broken off from its body by an ancient collision. The goddess Haumea was also a personification of stone,[8] and her namesake is believed to be almost entirely rock, atypical among known Kuiper belt objects (see Size and composition section). Ortiz et al. had reportedly proposed the name "Ataecina", which, as a chthonic deity, would not have been appropriate for a KBO not in resonance with Neptune.[9]

Discovery controversy

File:41354795 object 203.jpg
(136108) Haumea is circled in red

José Luis Ortiz Moreno, an astronomer at the Sierra Nevada Observatory in Spain, and colleagues Francisco José Aceituno Castro and Pablo Santos-Sanz announced the discovery of the object as the "tenth planet" on July 25, 2005, when they re-analysed observations they had made on March 7, 2003. They then scoured older archives (a process known as precovery) and found the object in images dating back to 1955.[10] Ortiz's group announced their discovery on July 27, 2005, and it was published two days later by the Minor Planet Center (MPC).[10]

A Caltech team consisting of Michael E. Brown, Chad Trujillo, and David Rabinowitz had been observing the object for half a year with the 1.3 m SMARTS Telescope, but had not yet made the data public. Brown and his collaborators initially supported giving Ortiz and his group credit for the discovery, but withdrew support when they found reason to suspect that Ortiz may have used discovery data from Brown's team, which had inadvertently been made publicly available on the web.[11]

A week before Ortiz's discovery announcement, on July 20, Brown's team had published an abstract of a report they intended to use to announce the discovery, in which the object was referred to by the internal code name K40506A. Typing this code into internet search engines allowed anyone to find the observation logs of Brown's group, including the observed positions of the object. Third-party web server logs indicated that the page in question had been accessed by an IP address used by computers at the Instituto de Astrofísica de Andalucía where Ortiz's group worked.[11] Brown's group accused Ortiz's group of a serious breach of scientific ethics and asked the MPC to strip them of discovery status.[12]

Ortiz later admitted he accessed the internet telescope logs with the relevant information a day before making his announcement, but denied any wrongdoing.[13] According to him, they did not use the data, other than checking them out of curiosity whether it could be the same object they had found in their 2003 images that same month, after they realized the object in the abstract by Brown et al. seemed to be an object with similar characteristics. Searching on the internet for the informal designation mentioned in the abstract, they ended up at the telescope log.[citation needed]

The ambiguity in who discovered the object stems from the fact that the Caltech group of Brown did not submit their discovery to the MPC for a year after detecting it in their images. The team had wanted to verify the nature of the body before making any announcement, and Brown was delayed in finishing his discovery paper by the birth of his daughter three weeks before the announcement of the Spanish team. Standing protocol is that discovery credit goes to whoever first submits a report to the MPC with enough positional data for a decent orbit determination. This is what Ortiz' group did, using their 2003 imagery, "precovery" positions from historic archives, and then—after further access to Brown's logs—fresh observations and additional precovery images.[citation needed]

According to Brown's account, on July 29, 2005, shortly after the Ortiz discovery announcement, Brown's group announced the discovery of another Kuiper belt object, Eris, which is more distant and is thought to be larger than Pluto. The announcement was made earlier than planned, at the MPC's urging, to forestall the possibility of a similar controversy with that discovery, as Brown et al's observation logs of Eris had by then also been publicly accessed.[7]

On 17 September, 2008, the International Astronomical Union gave the object Brown's name. However, the name of the discoverer was left blank on the announcement, and the location of discovery was still listed as the Sierra Nevada Observatory, Spain.[4][9] Brian Marsden, head of the IAU's Minor Planet Center at Harvard, openly supported Brown's claim, saying, "Sooner or later, posterity will realise what happened, and Mike Brown will get the full credit".[9]

Size and composition

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The only information that can be used to estimate the size of a small trans-Neptunian object is its optical magnitude, assuming a value for the albedo. For larger, brighter objects, the thermal emission can also be measured. Since the distance of the object from the Sun is already known, from the object's apparent rate of motion across the sky, its size and albedo can then be calculated.[1] Haumea is exceptional because its two moons provide the means to also directly determine the mass of the system from Kepler's third law, as the periods of the moons' orbits are determined by the masses in the system. The estimated mass is 4.2 × 1021 kg, 28% the mass of the Plutonian system.[14] Because Haumea rotates roughly once every four hours, faster than any other known body in the solar system larger than 100 km in diameter, it should be distorted into a triaxial ellipsoid.[15] The short rotation period of Haumea is likely to have been caused by a giant impact, which also created its satellites (See Collisional family section).[16]

The ellipsoid shape of Haumea, 1960×1518×996 km. At left are the minimum and maximum shapes seen at the equator (1960×996 and 1518×996 km); at right is the view from the pole (1960×1518 km).

Haumea displays large fluctuations in brightness. Although these fluctuations could be due to a mottled surface, it is thought that this fluctuation is due to an elongated shape. Rapid rotation and elongated shape result in constraints on the density (the denser the object, the less elongated), estimated at 2.6–3.3 g/cm³, suggesting substantial non-ice content (compare with Pluto's density of 2.0 g/cm³ and Earth's moon's density of 3.3 g/cm³). These limits on the density, together with the known mass, give another way to constrain the dimensions of the object.[15] Haumea has approximately the diameter of Pluto along its longest dimension, and half that along its shortest. This would make it one of the largest trans-Neptunian objects discovered so far; possibly fourth after Eris, Pluto and arguably Makemake, but larger than Sedna, Orcus, and Quaoar.[citation needed]

Surface

The Gemini telescope obtained spectra of Haumea, which show strong water ice features similar to the surface of Pluto's moon Charon. Trujillo, Brown, et al. report crystalline water ice.[17] Water ice has been reported on many trans-Neptunian objects but typically in the form of amorphous ice. Crystalline ice is unstable on timescales of 10 million years under conditions in the Kuiper Belt. This discovery hints at resurfacing processes producing fresh ice. Similarly surprising to the crystalline form is the inferred amount of ice. Following the report, the surface of Haumea appears to be 66% to 80% pure ice, with the remainder of the surface material of unknown composition. The ice is most likely a 50/50 mixture of crystalline and amorphous forms.[18] The purity of the ice on Haumea's surface suggests that the object essentially consists of a thin layer of ice surrounding a core of rock.[17]

Haumea has an albedo approaching that of pure snow, consistent with crystalline ice on the surface. This very high albedo does not appear to be unique among large TNOs. Recent measurements of Eris imply an even higher (inferred) albedo (0.86) for that object.[19] The surface of Haumea is depleted in carbon chains, which makes it a possible source for the carbon-depleted Jupiter family comets.[18]

Orbit

Orbits of Haumea (yellow) and Pluto (red).

Haumea is classified as a classical trans-Neptunian object with an orbit common for large cubewanos: the perihelion is close to 35 AU and significantly inclined. The diagram shows a view of its orbit in yellow, (Pluto in red, Neptune in grey) and position (as of April 2006). The object passed its aphelion (Q) in 1991,[citation needed] and is currently more than 50 AU from the Sun and takes 285 Earth years for a complete orbit.

Haumea's orbit lies slightly higher than the other members of its collisional family, and this may be due to the object's possibly being in a 12:7 resonance with Neptune, which has gradually shifted its orbit over the course of the last billion years.[20]

The inclination of its orbit (~28° to compare with 17° for Pluto) and its current position, far from the ecliptic where most of the early surveys took place, combined with a slow mean motion explain why Haumea was only discovered recently, in spite of its magnitude.[original research?]

Moons

Main article: Moons of Haumea

Two small satellites have been discovered orbiting Haumea; (136108) Haumea I Hiʻiaka, and (136108) Haumea II Namaka.[4]

Hiʻiaka

Hiʻiaka or Haumea I, nicknamed "Rudolph" by the Caltech team, was the first satellite discovered around Haumea, announced on January 26, 2005. The outer of Haumea's two known satellites, it orbits once every 49 days. The discovery team missed by only a few years mutual occultations of Hiʻiaka and Haumea, which occurred in 1999 and will not occur again until 2138.

Assuming Hiʻiaka has the same density and albedo as Haumea, its mass is 1% that of the mass of Haumea and its diameter is approximately 310 km.[21][original research?]

Strong absorption features at 1.5 and 2 micrometres discovered in the infrared spectrum are consistent with absorption due to water ice. Their depth suggests that much of the satellite’s surface is covered with ice.[22] Hiʻiaka's water ice absorption spectrum is stronger than that of any other body in the Solar System. This unique feature, and similar absorption lines observed on Haumea itself, led Brown et. al. to conclude that capture was an unlikely model for the system's formation, and that Haumea's moons must have been split off from Haumea itself.[20]

Namaka

Namaka or Haumea II, nicknamed "Blitzen" by the Caltech team,[23] is the smaller inner satellite of Haumea. Its discovery was announced on November 7, 2005. It is inclined 39 ± 6° from the larger moon, but as of 2008 its orbit is not yet known.

The measured brightness implies a diameter 12% that of Haumea, or some 170 km, assuming a similar surface composition.

Collisional family

Main article: Haumea family

Haumea is the largest member of a TNO collisional family, similar to asteroid families: a group of objects with similar orbital parameters and common physical characteristics, presumably with a common origin in a disruptive impact of the progenitor object of Haumea.[16]

The family, the first to be identified among TNOs, includes Haumea and its moons, 2002 TX300, (24835) 1995 SM55, (19308) 1996 TO66, (120178) 2003 OP32 and (145453) 2005 RR43.

The presence of the collisional family hints 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 is less than 0.1 percent. The family could not have formed in the denser primordial Kuiper belt because such a close-knit group would have been disrupted by Neptune's subsequent migration into the belt, which is believed to have been the cause of its current low density. Therefore it appears likely that the dynamic scattered disc region, in which the possibility of such a collision is far higher, is the place of origin for the object which would become Haumea and its kin.[24] 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.[25]

References

  1. ^ a b John Stansberry, Will Grundy, Mike Brown, Dale Cruikshank, John Spencer, David Trilling, Jean-Luc Margot (2007). "Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope". University of Arizona, Lowell Observatory, California Institute of Technology, NASA Ames Research Center, Southwest Research Institute, Cornell University. Retrieved 2008-07-27.{{cite web}}: CS1 maint: multiple names: authors list (link)
  2. ^ "HORIZONS Web-Interface". JPL Solar System Dynamics. Retrieved 2008-07-02. {{cite web}}: External link in |publisher= (help)
  3. ^ "JPL Small-Body Database Browser: 136 108 (2003 EL61)". 2008-05-10 last obs. Retrieved 2008-06-11. {{cite web}}: Check date values in: |date= (help)
  4. ^ a b c "USGS Gazetteer of Planetary Nomenclature". Retrieved 2008-09-17.
  5. ^ a b "IAU names fifth dwarf planet Haumea". IAU Press Release. September 17, 2008. Retrieved 2008-09-17.
  6. ^ "Naming of astronomical objects: Minor planets". International Astronomical Union. Retrieved 2008-11-17.
  7. ^ a b Mike Brown (2008). "Haumea". CalTech. Retrieved 2008-09-18.
  8. ^ "News Release - IAU0807: IAU names fifth dwarf planet Haumea". International Astronomical Union. 2008. Retrieved 2008-09-18.
  9. ^ a b c Rachel Courtland (2008). "Controversial dwarf planet finally named 'Haumea'". NewScientistSpace. Retrieved 2008-09-19.
  10. ^ a b "Minor Planet Electronic Circular 2005-O36 : 2003 EL61".
  11. ^ a b Michael E Brown. "The electronic trail of the discovery of 2003 EL61". CalTech. Retrieved 2006-08-16.
  12. ^ "One Find, Two Astronomers: An Ethical Brawl". New York Times. September 13, 2005. Retrieved 2006-08-16. {{cite news}}: Unknown parameter |name= ignored (help)
  13. ^ "Astronomer denies improper use of web data". NewScientist.com. September 21, 2005. Retrieved 2006-08-16. {{cite news}}: Unknown parameter |name= ignored (help)
  14. ^ M. E. Brown, A. H. Bouchez, D. L. Rabinowitz, R. Sari, C. A. Trujillo, M. A. van Dam, R. Campbell, J. Chin, S. Hartman, E. Johansson, R. Lafon, D. LeMignant, P. Stomski, D. Summers, P. L. Wizinowich Keck Observatory laser guide star adaptive optics discovery and characterization of a satellite to large Kuiper belt object 2003 EL61, The Astrophysical Journal Letters, 632, L45 (October 2005) Full text from Caltech
  15. ^ a b D. L. Rabinowitz, K. M. Barkume, M. E. Brown, H. G. Roe, M. Schwartz, S. W. Tourtellotte, C. A. Trujillo (2005), Photometric Observations Constraining the Size, Shape, and Albedo of 2003 EL61, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt, The Astrophysical Journal (2006), 639, Issue 2, pp. 1238-1251 Preprint on arXiv
  16. ^ a b Michael E. Brown, Kristina M. Barkume; Darin Ragozzine; Emily L. Schaller (2007). "A collisional family of icy objects in the Kuiper belt". Nature. 446 (7133): 294–296. doi:10.1038/nature05619. {{cite journal}}: Cite has empty unknown parameter: |month= (help)CS1 maint: multiple names: authors list (link)
  17. ^ a b Chadwick A. Trujillo, Michael E. Brown, Kristina Barkume, Emily Shaller, David Rabinowitz; The Surface of 2003 EL61 in the Near Infrared. The Astrophysical Journal, 655 (Feb. 2007), pp. 1172-1178 Preprint
  18. ^ a b N. Pinilla-ALonso, R. Brunetto, J. Licandro, R. Gil-Hutton, T.L. Roush, G. Strazzulla. "Study of the Surface of 2003 EL61: the largest carbon-depleted object in the trans-neptunian belt". Astronomy & Astrophysics. {{cite journal}}: Cite has empty unknown parameter: |1= (help); Unknown parameter |acessdate= ignored (|access-date= suggested) (help)CS1 maint: multiple names: authors list (link)
  19. ^ M. E. Brown, E.L. Schaller, H.G. Roe, D. L. Rabinowitz, C. A. Trujillo (2006). "Direct measurement of the size of 2003 UB313 from the [[Hubble Space Telescope]]" (PDF). The Astronomical Journal. 643 (2): L61–L63. doi:10.1086/504843. {{cite journal}}: URL–wikilink conflict (help)CS1 maint: multiple names: authors list (link)
  20. ^ a b Michael E. Brown. "The largest Kuiper belt objects" (PDF). CalTech. Retrieved 2008-09-19.
  21. ^ "List Of Transneptunian Objects". Minor Planet Center. 2008. Retrieved 2008-09-19.
  22. ^ K. M Barkume, M. E. Brown, and E. L. Schaller Water Ice on the Satellite of Kuiper Belt Object 2003 EL61,The Astrophysical Journal, 640 (March 2006), pp. L87-L89. Preprint
  23. ^ Kenneth Chang (2007-03-20). "Piecing Together the Clues of an Old Collision, Iceball by Iceball". New York Times.
  24. ^ Harold F. Levison, Alessandro Morbidelli, David Vokrouhlický and William F. Bottke (2008). "On a Scattered Disc Origin for the 2003 EL61 Collisional Family— an Example of the Importance of Collisions in the Dynamics of Small Sodies". The Astronomical Journal. 136: 1079–1088. doi:10.1088/0004-6256/136/3/1079. Retrieved 2008-09-19.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  25. ^ D. Ragozzine; M. E. Brown (2007). "Candidate Members and Age Estimate of the Family of Kuiper Belt Object 2003 EL61". The Astronomical Journal. 134 (6): 2160–2167. Retrieved 2008-09-19.{{cite journal}}: CS1 maint: multiple names: authors list (link)

News coverage

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