View source for Astronomy:10 Hygiea

{{Short description|Major asteroid}}
{{Infobox planet
 | minorplanet     = yes
 | background      = #D6D6D6
 | name            = 10 Hygiea
 | symbol          = [[File:Hygiea symbol (original, bold).svg|24px|The original planetary symbol for 10 Hygiea|alt=A zeta-shaped serpent crowned with a star]] (historical astronomical), [[File:Hygiea astrological symbol (bold).svg|24px|⯚]] (modern astrological)
 | image           = SPHERE image of Hygiea.jpg
 | image_scale      =
 | caption         = VLT-SPHERE image of Hygiea
 | discovery_ref   = <ref name="jpldata" />
 | discoverer      = [[Biography:Annibale de Gasparis|A. de Gasparis]]
 | discovery_site  = Astronomical Observatory of Capodimonte
 | discovered      = 12 April 1849
 | pronounced      = {{IPAc-en|h|aɪ|ˈ|dʒ|iː|ə}}<ref>{{OED|Hygeia}}</ref>
 | adjectives      = Hygiean {{IPAc-en|h|aɪ|ˈ|dʒ|iː|ə|n}}<ref>{{OED|hygeian}}</ref> 
 | mpc_name        = (10) Hygiea
 | alt_names       = A900 GA
 | named_after     = Hygieia<ref name="springer" />
 | mp_category     = [[Astronomy:Asteroid belt|Main belt]] ([[Astronomy:Hygiea family|Hygiea family]])
 | orbit_ref       = <ref name="jpldata" />
 | epoch           = 27 April 2019 ([[Astronomy:Julian day|JD]] 2458600.5)
 | uncertainty     = 0
 | observation_arc = {{nowrap|170.23 yr (62,175 days)}}
 | aphelion        = 3.4948 [[Astronomy:Astronomical unit|AU]]
 | perihelion      = 2.7882 AU
 | semimajor       = 3.1415 AU
 | eccentricity    = 0.1125
 | period          = 5.57 [[Astronomy:Julian year|yr]] (2033.8 days)
 | mean_anomaly    = 152.18[[Degree (angle)|°]]
 | inclination     = 3.8316°
 | asc_node        = 283.20°
 | arg_peri        = 312.32°
 | surface_area    = 
 | avg_speed       = 16.76 km/s
 | p_orbit_ref = <ref name=Hygiea-POE/>
| p_semimajor = 3.14178
| p_eccentricity = 0.1356
| p_inclination = 5.1039°
| p_mean_motion = 64.6218
| perihelion_rate = 128.544
| node_rate = −96.9024
| dimensions = c/a = {{val|.94|.05}}<ref name=VLT/><br />{{val|450|x|430|x|424|u=km}}<br />{{small|± {{val|10|x|10|x|20|u=km}}}}
| mean_diameter = {{val|433|8|u=km}}<ref name=VLT>P. Vernazza et al. (2021) VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis. ''Astronomy & Astrophysics'' 54, A56</ref><br />{{val|434|14|u=km}}<ref name=Vernazza2019/>
| mass = {{val|8.74|0.69|e=19|u=kg}}<ref name=VLT/><br />{{val|8.32|0.80|e=19|u=kg}} (representative)<ref name=Vernazza2019b/>
| density={{val|2.06|.20|u=g/cm3}}<ref name=VLT/><br />{{val|1.94|0.19|u=g/cm3}}<ref name=Vernazza2019b/>
| surface_grav=
| escape_velocity=
| rotation={{val|13.82559|0.00005}} h<ref name=Vernazza2019/>
| spectral_type=[[Astronomy:C-type asteroid|C-type]]<ref name=jpldata/>
| magnitude=9.0<ref name=AstDys-Hygiea/><!-- Horizons 2011-May-14 --> to 11.97
| abs_magnitude=5.43<ref name=jpldata/>
| albedo=0.063<ref name=VLT/><br />0.0717&nbsp;<ref name=jpldata/>
| angular_size = 0.321″ <!-- Horizons 2078-May-20 --> to 0.133″
| single_temperature=≈164 [[Kelvin|K]]<br />''max:'' 247 K (−26°C)<ref name="Lim2005"/>
}}

'''Hygiea''' ([[Astronomy:Minor-planet designation|minor-planet designation]]: '''10 Hygiea''') is a major [[Astronomy:Asteroid|asteroid]] located in the main asteroid belt. With a mean diameter of between {{val|425|and|440}} km and a mass estimated to be 3% of the total mass of the belt,<ref>"Mass of 10 Hygiea" 0.445 / [http://iau-comm4.jpl.nasa.gov/EPM2004.pdf "Mass of Mbelt"] {{webarchive|url=https://web.archive.org/web/20081031065523/http://iau-comm4.jpl.nasa.gov/EPM2004.pdf |date=2008-10-31 }} 15 = 0.0296</ref> it is the fourth-largest asteroid in the [[Astronomy:Solar System|Solar System]] by both volume and mass, and is the largest of the [[Astronomy:C-type asteroid|C-type asteroid]]s (dark asteroids with a carbonaceous surface) in classifications that use [[Astronomy:G-type asteroid|G type]] for [[Astronomy:1 Ceres|1 Ceres]]. It is very close to spherical, apparently because it had re-accreted after the disruptive impact that produced the large Hygiean family of asteroids.

==Observation==
[[File:10 Hygiea 2MASS.jpg|thumb|left|upright|Image of 10 Hygiea taken by the [[Astronomy:2MASS|2MASS]] survey]]
Despite its size, Hygiea appears very dim when observed from [[Astronomy:Earth|Earth]]. This is due to its dark surface and its position in the [[Astronomy:Asteroid belt#Orbits|outer main belt]]. For this reason, six smaller asteroids were observed before [[Biography:Annibale de Gasparis|Annibale de Gasparis]] discovered Hygiea on 12 April 1849. At most [[Astronomy:Opposition (planets)|oppositions]], Hygiea has a [[Astronomy:Apparent magnitude|magnitude]] that is four magnitudes dimmer than [[Astronomy:4 Vesta|Vesta's]], and observing it typically requires at least a {{convert|100|mm|in|adj=on|0}} [[Astronomy:Telescope|telescope]]. However, while at a perihelic opposition, it can be observed just with 10×50 binoculars as Hygiea would have a magnitude of +9.1.<ref name="inthesky"/>

==Discovery and name==
On 12 April 1849, in Naples, Italy, astronomer [[Biography:Annibale de Gasparis|Annibale de Gasparis]] (age 29) discovered Hygiea.<ref name=Leuschner1922/> It was the first of his nine asteroid discoveries. The director of the Naples observatory, Ernesto Capocci, named the asteroid. He chose to call it ''Igea Borbonica'' ("Bourbon Hygieia"), after the Greek goddess of health, daughter of [[Religion:Asclepius|Asclepius]], and in honor of the ruling family of the Kingdom of the Two Sicilies where Naples was located.<ref name=Hind1852/>

In 1852, [[Biography:John Russell Hind|John Russell Hind]] wrote that "it is universally termed ''Hygiea'', the unnecessary appendage 'Borbonica' being dropped."<ref name=Hind1852/> The English form is an irregular spelling of Greek ''Hygieia'' or ''Hygeia'' (Latin ''Hygea'' or ''Hygia'').<ref name=Barucci/>

===Symbol===
The intended astronomical symbol for Hygiea was a zeta-shaped serpent crowned with a star, in the pipeline for [[Unicode]] 17.0 as U+1F779 🝹 {{nowrap|([[File:Hygiea symbol (original, fixed width).svg|24px|The traditional planetary symbol for 10 Hygiea|alt=A zeta-shaped serpent crowned with a star]]);}}<ref name=astunicode>{{cite web |url=https://www.unicode.org/L2/L2023/23207-historical-asteroids.pdf |title=Unicode request for historical asteroid symbols |last1=Bala |first1=Gavin Jared |last2=Miller |first2=Kirk |date=18 September 2023 |website=unicode.org |publisher=Unicode |access-date=26 September 2023 |quote=}}</ref><ref name=pipeline>{{cite web |url=https://unicode.org/alloc/Pipeline.html |title=Proposed New Characters: The Pipeline |author=Unicode |date= |website=unicode.org |publisher=The Unicode Consortium |access-date=6 November 2023 |quote=}}</ref> the serpent and serpent [[Bowl of Hygieia|drinking from a bowl]] are traditional symbols of the goddess Hygieia (cf. U+1F54F 🕏). In later years it was substituted with a [[Rod of Asclepius|rod of Asclepius]]: 24px|rod of Asclepius (a serpent twined around a staff, U+2695 ⚕), confusing Hygieia with her masculine counterpart. These symbols are now both largely obsolete. In this century, 10 Hygiea has seen some minor astrological use, and its symbol was confused once again, with Asclepsius's rod replaced by Mercury's [[Caduceus|caduceus]]: 24px|Astrological symbol for Hygiea,<ref name="L216080">{{cite web|url=https://www.unicode.org/L2/L2016/16080r-add-astrology.pdf|title=L2/16-080: Additional Symbols for Astrology|date=2016-05-28|first=David|last=Faulks|access-date=22 May 2023|archive-date=11 May 2022|archive-url=https://web.archive.org/web/20220511233510/https://www.unicode.org/L2/L2016/16080r-add-astrology.pdf|url-status=live}}</ref> though in a more elaborate form (U+2BDA ⯚) than the symbol of the planet Mercury. The caduceus has [[Medicine:Caduceus as a symbol of medicine|long been mistaken for]] the rod of Asclepius.

==Physical characteristics==
[[File:The Four Largest Asteroids.jpg|thumb|left|Relative sizes of the four largest asteroids. Hygiea is furthest right.]]
[[File:Hygiea imaging SPHERE.png|thumb|left|VLT-SPHERE images of asteroid 10 Hygiea, taken in June/July 2017. A bright surface feature and several dark craters are visible on the surface. At the time, the southern hemisphere of Hygiea was facing Earth.]]
[[File:Iau dozen.jpg|thumb|left|The IAU 2006 draft proposal listed Hygiea as a potential planet.<ref name="IAU-draft2006"/>]]

Observations taken with the [[Astronomy:Very Large Telescope|Very Large Telescope]]'s SPHERE imager in 2017 and 2018 revealed that Hygiea is nearly spherical and is close to a [[Astronomy:Hydrostatic equilibrium|hydrostatic equilibrium]] shape.<ref name=Vernazza2019/>
Based on spectral evidence, Hygiea's surface is thought to consist of primitive carbonaceous materials similar to those found in carbonaceous chondrite [[Astronomy:Meteorite|meteorite]]s. [[Chemistry:Aqueous|Aqueous]] alteration products have been detected on its surface, which could indicate the presence of water ice in the past which was heated sufficiently to melt.<ref name=Barucci/> The primitive present surface composition indicates that Hygiea had not melted during the early period of Solar System formation.<ref name=Barucci/>  However, observations suggest Hygiea suffered a major collision early in its history that completely disrupted it, with its present spherical shape due to re-accretion of the disrupted material.<ref name=VLT/> No deep basins are visible in VLT images, indicating that any large craters that formed after re-accretion must have flat floors, consistent with an icy C-type composition.<ref name=Vernazza2019/>

In images taken with the VLT in 2017, a bright surface feature is visible, as well as at least two dark craters, which have been informally{{efn|Pending approval by the [[Organization:International Astronomical Union|IAU]].}} named Serpens and Calix after the Latin words for 'snake' and 'cup', respectively.<ref name=Vernazza2019b/> Serpens has a diameter of 180&nbsp;km, Calix of 90&nbsp;km.<ref name=Vernazza2019b/><ref name=Vernazza2019/>

Hygiea is the largest of the class of dark [[Astronomy:C-type asteroid|C-type asteroid]]s that are dominant in the outer asteroid belt, beyond the [[Astronomy:Kirkwood gap|Kirkwood gap]] at 2.82 AU.<ref name="ESA C-type"/> Its mean diameter {{val|433|8|u=km}}.<ref name=VLT/> Hygiea is close to spherical, with an axis ratio of {{val|0.94|0.05}} that is consistent with a MacLaurin ellipsoid.<ref name=VLT/> Aside from being the smallest of the "big four", Hygiea has a relatively low density of {{val|2.06|0.20}},<ref name="VLT"/> comparable to Ceres (2.16) and the larger icy satellites of the Solar System (Ganymede 1.94, Callisto 1.83, Titan 1.88, Triton 2.06) rather than to Pallas ({{val|2.9|0.1}}) or Vesta (3.45).

Although it is the largest body in its region, due to its dark surface and farther-than-average distance from the Sun, Hygiea appears very dim when observed from Earth. In fact, it is the third dimmest of the first twenty-three asteroids discovered, with only [[Astronomy:13 Egeria|13 Egeria]] and [[Astronomy:17 Thetis|17 Thetis]] having lower mean opposition [[Astronomy:Magnitude|magnitude]]s.<ref name=brightestasteroids/> At most oppositions, Hygiea has a [[Astronomy:Apparent magnitude|magnitude]] of around +10.2,<ref name=brightestasteroids/> which is as much as four orders fainter than Vesta, and observation calls for at least a {{convert|4|in|mm|adj=on}} [[Astronomy:Telescope|telescope]] to resolve.<ref name=telescope/> However, at a perihelic opposition, Hygiea can reach +9.1 magnitude and may just be resolvable with 10 × 50 binoculars, unlike the next two largest asteroids in the asteroid belt, [[Astronomy:704 Interamnia|704 Interamnia]] and [[Astronomy:511 Davida|511 Davida]], which are always beyond binocular visibility.<ref name="inthesky"/>

A total of 17 [[Astronomy:Star|stellar]] [[Astronomy:Occultation|occultation]]s by Hygiea have been tracked by Earth-based astronomers,<ref name=Watanabe/><ref name=Hilton2008/> including two (in 2002 and 2014) that were seen by a large number of observers. The observations have been used to constrain Hygiea's size, shape and rotation axis.<ref name=Hanus2017/> The [[Astronomy:Hubble Space Telescope|Hubble Space Telescope]] has resolved the asteroid and ruled out the presence of any orbiting companions larger than about {{convert|16|km|mi}} in diameter.<ref name="Storrs1999"/>

==Orbit and rotation==
[[File:AnimatedOrbitOf10Hygiea.gif|thumb|Animated orbit of Hygiea relative to the orbits of the terrestrial planets and Jupiter|left]]
Orbiting at an average of 3.14 AU from the Sun, Hygiea is the most distant of the "big four" asteroids. It lies closer to the [[Astronomy:Ecliptic|ecliptic]] as well, with an orbital inclination of 4°.<ref name=Barucci/> Its orbit is less circular than those of Ceres or Vesta, with an eccentricity of around 0.12.<ref name=jpldata /> Its [[Astronomy:Apsis|perihelion]] is at a quite similar longitude to those of Vesta and Ceres, though its ascending and descending nodes are opposite to the corresponding ones for those objects. Although its perihelion is extremely close to the mean distance of Ceres and Pallas, a collision between Hygiea and its larger companions is impossible because at that distance they are always on opposite sides of the ecliptic.{{citation needed|date=October 2019|reason=The relevance of this and the sentence that precedes it is questionable. None of this is mentioned in the source.}} In 2056, Hygiea will pass 0.025&nbsp;AU from Ceres, and then in 2063, Hygiea will pass 0.020&nbsp;AU from Pallas.<ref name=jpl-close/>{{failed verification|date=October 2019}} At [[Astronomy:Apsis|aphelion]] Hygiea reaches out to the extreme edge of the asteroid belt at the perihelia of the Hilda family, which is in a 3:2 orbital resonance with Jupiter.<ref name="L'vov" />

As one of the most massive asteroids, Hygiea is used by the [[Organization:Minor Planet Center|Minor Planet Center]] to calculate [[Astronomy:Perturbation|perturbations]].<ref name="Perturbing"/>

Hygiea is in an unstable three-body mean motion resonance with Jupiter and Saturn.<ref name="Nesvorny1998"/> The computed [[Lyapunov time]] for this asteroid is 30,000 years, indicating that it occupies a chaotic orbit that will change randomly over time because of gravitational perturbations by the planets.<ref name="Nesvorny1998"/> It is the lowest numbered asteroid in such a resonance (the next lowest numbered being [[Astronomy:70 Panopaea|70 Panopaea]]).<ref name="Nesvorny1998"/><ref name="AstDys_res"/>

Hygiea has a rotation period of 13.83 hours.<ref name=Vernazza2019/> Its single-peaked light curve has an amplitude of 0.27 mag,<ref name=Vernazza2019b/> which is largely attributed to [[Earth:Albedo|albedo]] variations.<ref name=Vernazza2019/> Hygiea's north pole points towards [[Astronomy:Ecliptic coordinate system|ecliptic longitude]] {{val|306|3|u=°}} and ecliptic latitude {{val|-29|3|u=°}},<ref name="VLT"/> which gives an [[Astronomy:Axial tilt|axial tilt]] of 119° with respect to the [[Astronomy:Ecliptic|ecliptic]].<ref name=VLT/>

==Hygiea family==
[[File:Hygiea_family.png|280px|thumb|Location and structure of the Hygiea family]]
{{main|Astronomy:Hygiea family}}
Hygiea is the main member of the Hygiean [[Astronomy:Asteroid family|asteroid family]] that constitutes about 1% of asteroids in the main belt.{{citation needed|date=October 2019}} The family was formed when an object with a diameter of about 100&nbsp;km collided with proto-Hygiea about 2 billion years ago. Because the impact craters on Hygiea today are too small to contain the volume of ejected material, it is thought that Hygiea was completely disrupted by the impact and that the majority of the debris recoalesced after the pieces that formed the rest of the family had escaped. Hygiea contains almost all the mass (over 98%) of the family.<ref name=Vernazza2019/>

==See also==
* [[Astronomy:Planet#Objects formerly considered planets|Former classification of planets]]

== Notes ==
{{notelist|group=lower-alpha}}

== References ==
{{reflist| refs =

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<ref name="jpldata">{{cite web
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<ref name=Vernazza2019>{{cite journal
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<ref name=Vernazza2019b>{{cite journal
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<ref name=Barucci>{{cite journal
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== External links ==
* [http://orbitsimulator.com/gravity/articles/ceres.html A simulation of the orbit of Hygiea]
* [https://www.youtube.com/watch?v=C-6s1LBaTsE Stellar occultation of 11 August 2013 (video)]
* {{cite web |title=Elements and Ephemeris for (10) Hygiea |publisher=Minor Planet Center |url=http://scully.cfa.harvard.edu/cgi-bin/returnprepeph.cgi?d=b2011&o=00010 |access-date=26 May 2011 <!--Added by DASHBot--> |url-status=dead |archive-url=https://web.archive.org/web/20160304112311/http://scully.cfa.harvard.edu/cgi-bin/returnprepeph.cgi?d=b2011&o=00010 |archive-date=4 March 2016 }} (displays [[Astronomy:Elongation|Elong]] from Sun and [[Astronomy:Apparent magnitude|V mag]] for 2011)
* {{AstDys|10}}
* {{JPL small body}}

{{Small Solar System bodies}}
{{Large asteroids}}

{{DEFAULTSORT:000010}}
[[Category:Hygiea asteroids]]
[[Category:Named minor planets|Hygiea]]
[[Category:Possible dwarf planets]]
[[Category:C-type asteroids (Tholen)]]
[[Category:C-type asteroids (SMASS)]]

{{Sourceattribution|10 Hygiea}}