10 Hygiea

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10 Hygiea
VLT-SPHERE image of Hygiea
Discovered byA. de Gasparis
Discovery siteAstronomical Observatory of Capodimonte
Discovery date12 April 1849
(10) Hygiea
Named after
A900 GA
Main belt (Hygiea family)
AdjectivesHygiean /hˈən/[4]
SymbolA zeta-shaped serpent crowned with a star (historical astronomical), ⯚ (modern astrological)
Orbital characteristics[1]
Epoch 27 April 2019 (JD 2458600.5)
Uncertainty parameter 0
Observation arc170.23 yr (62,175 days)
Aphelion3.4948 AU
Perihelion2.7882 AU
3.1415 AU
5.57 yr (2033.8 days)
16.76 km/s
Proper orbital elements[5]
3.14178 AU
64.6218 deg / yr
5.57088 yr
(2034.762 d)
Precession of perihelion
128.544 arcsec / yr
Precession of the ascending node
−96.9024 arcsec / yr
Physical characteristics
Dimensionsc/a = 0.94±0.05[6]
450 km × 430 km × 424 km
± 10 km × 10 km × 20 km
Mean diameter
433±8 km[6]
434±14 km[7]
Mass(8.74±0.69)×1019 kg[6]
(8.32±0.80)×1019 kg (representative)[8]
Mean density
2.06±0.20 g/cm3[6]
1.94±0.19 g/cm3[8]
13.82559±0.00005 h[7]
0.0717 [1]
Temperature≈164 K
max: 247 K (−26°C)[9]
9.0[10] to 11.97
0.321″ to 0.133″

Hygiea (minor-planet designation: 10 Hygiea) is a major asteroid located in the main asteroid belt. With a mean diameter of between 425 and 440 km and a mass estimated to be 3% of the total mass of the belt,[11] it is the fourth-largest asteroid in the Solar System by both volume and mass, and is the largest of the C-type asteroids (dark asteroids with a carbonaceous surface) in classifications that use G type for 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.


Image of 10 Hygiea taken by the 2MASS survey

Despite its size, Hygiea appears very dim when observed from Earth. This is due to its dark surface and its position in the outer main belt. For this reason, six smaller asteroids were observed before Annibale de Gasparis discovered Hygiea on 12 April 1849. At most oppositions, Hygiea has a magnitude that is four magnitudes dimmer than Vesta's, and observing it typically requires at least a 100-millimetre (4 in) 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.[12]

Discovery and name[edit]

On 12 April 1849, in Naples, Italy, astronomer Annibale de Gasparis (age 29) discovered Hygiea.[13] 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 Asclepius, and in honor of the ruling family of the Kingdom of the Two Sicilies where Naples was located.[14]

In 1852, John Russell Hind wrote that "it is universally termed Hygiea, the unnecessary appendage 'Borbonica' being dropped."[14] The English form is an irregular spelling of Greek Hygieia or Hygeia (Latin Hygea or Hygia).[15]


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 🝹 (A zeta-shaped serpent crowned with a star);[16][17] the serpent and serpent 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 (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: Astrological symbol for Hygiea,[18] though in a more elaborate form (U+2BDA ⯚) than the symbol of the planet Mercury. The caduceus has long been mistaken for the rod of Asclepius.

Physical characteristics[edit]

Relative sizes of the four largest asteroids. Hygiea is furthest right.
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.
The IAU 2006 draft proposal listed Hygiea as a potential planet.[19]

Observations taken with the Very Large Telescope's SPHERE imager in 2017 and 2018 revealed that Hygiea is nearly spherical and is close to a hydrostatic equilibrium shape.[7] Based on spectral evidence, Hygiea's surface is thought to consist of primitive carbonaceous materials similar to those found in carbonaceous chondrite meteorites. 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.[15] The primitive present surface composition indicates that Hygiea had not melted during the early period of Solar System formation.[15] 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.[6] 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.[7]

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[a] named Serpens and Calix after the Latin words for 'snake' and 'cup', respectively.[8] Serpens has a diameter of 180 km, Calix of 90 km.[8][7]

Hygiea is the largest of the class of dark C-type asteroids that are dominant in the outer asteroid belt, beyond the Kirkwood gap at 2.82 AU.[20] Its mean diameter 433±8 km.[6] Hygiea is close to spherical, with an axis ratio of 0.94±0.05 that is consistent with a MacLaurin ellipsoid.[6] Aside from being the smallest of the "big four", Hygiea has a relatively low density of 2.06±0.20,[6] 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 (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 13 Egeria and 17 Thetis having lower mean opposition magnitudes.[21] At most oppositions, Hygiea has a magnitude of around +10.2,[21] which is as much as four orders fainter than Vesta, and observation calls for at least a 4-inch (100 mm) telescope to resolve.[22] 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, 704 Interamnia and 511 Davida, which are always beyond binocular visibility.[12]

A total of 17 stellar occultations by Hygiea have been tracked by Earth-based astronomers,[23][24] 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.[25] The Hubble Space Telescope has resolved the asteroid and ruled out the presence of any orbiting companions larger than about 16 kilometres (9.9 mi) in diameter.[26]

Orbit and rotation[edit]

Animated orbit of Hygiea relative to the orbits of the terrestrial planets and Jupiter

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 ecliptic as well, with an orbital inclination of 4°.[15] Its orbit is less circular than those of Ceres or Vesta, with an eccentricity of around 0.12.[1] Its 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] In 2056, Hygiea will pass 0.025 AU from Ceres, and then in 2063, Hygiea will pass 0.020 AU from Pallas.[27][failed verification] At 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.[28]

As one of the most massive asteroids, Hygiea is used by the Minor Planet Center to calculate perturbations.[29]

Hygiea is in an unstable three-body mean motion resonance with Jupiter and Saturn.[30] 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.[30] It is the lowest numbered asteroid in such a resonance (the next lowest numbered being 70 Panopaea).[30][31]

Hygiea has a rotation period of 13.83 hours.[7] Its single-peaked light curve has an amplitude of 0.27 mag,[8] which is largely attributed to albedo variations.[7] Hygiea's north pole points towards ecliptic longitude 306°± and ecliptic latitude −29°±,[6] which gives an axial tilt of 119° with respect to the ecliptic.[6]

Hygiea family[edit]

Location and structure of the Hygiea family

Hygiea is the main member of the Hygiean asteroid family that constitutes about 1% of asteroids in the main belt.[citation needed] The family was formed when an object with a diameter of about 100 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.[7]

See also[edit]


  1. ^ Pending approval by the IAU.


  1. ^ a b c d e f "JPL Small-Body Database Browser: 10 Hygiea" (2019-08-18 last obs.). Jet Propulsion Laboratory. Archived from the original on 5 November 2020. Retrieved 28 October 2019.
  2. ^ "Hygeia". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  3. ^ Schmadel, L. D. (2007). "(10) Hygiea". Dictionary of Minor Planet Names – (10) Hygiea. Springer Berlin Heidelberg. p. 16. doi:10.1007/978-3-540-29925-7_11. ISBN 978-3-540-29925-7.
  4. ^ "hygeian". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  5. ^ "AstDyS-2 Hygiea Synthetic Proper Orbital Elements". Department of Mathematics, University of Pisa, Italy. Archived from the original on 15 November 2020. Retrieved 28 April 2019.
  6. ^ a b c d e f g h i j k P. Vernazza et al. (2021) VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis. Astronomy & Astrophysics 54, A56
  7. ^ a b c d e f g h Vernazza, P.; Jorda, L.; Ševeček, P.; Brož, M.; Viikinkoski, M.; Hanuš, J.; et al. (2020). "A basin-free spherical shape as an outcome of a giant impact on asteroid Hygiea" (PDF). Nature Astronomy. 273 (2): 136–141. Bibcode:2020NatAs...4..136V. doi:10.1038/s41550-019-0915-8. hdl:10045/103308. S2CID 209938346. Archived (PDF) from the original on 11 November 2020. Retrieved 28 October 2019.
  8. ^ a b c d e Vernazza, P.; Jorda, L.; Ševeček, P.; Brož, M.; Viikinkoski, M.; Hanuš, J.; et al. (28 October 2019). "A basin-free spherical shape as an outcome of a giant impact on asteroid Hygiea, Supplementary Information" (PDF). Nature Astronomy. 4. Bibcode:2020NatAs...4..136V. doi:10.1038/s41550-019-0915-8. hdl:10045/103308. S2CID 209938346. Archived (PDF) from the original on 29 November 2021. Retrieved 30 October 2019.
  9. ^ Lim, L. F.; McConnochie, T.; Belliii, J.; Hayward, T. (2005). "Thermal infrared (8–13 μm) spectra of 29 asteroids: the Cornell Mid-Infrared Asteroid Spectroscopy (MIDAS) Survey". Icarus. 173 (2): 385. Bibcode:2005Icar..173..385L. doi:10.1016/j.icarus.2004.08.005.
  10. ^ "AstDys (10) Hygiea Ephemerides". Department of Mathematics, University of Pisa, Italy. Archived from the original on 24 July 2020. Retrieved 26 June 2010.
  11. ^ "Mass of 10 Hygiea" 0.445 / "Mass of Mbelt" Archived 2008-10-31 at the Wayback Machine 15 = 0.0296
  12. ^ a b Ford, D. (29 June 2017). "Asteroid 10 Hygiea at opposition". in-the-sky.org. Archived from the original on 27 November 2021. Retrieved 14 March 2019.
  13. ^ Leuschner, A. O. (15 July 1922). "Comparison of Theory with Observation for the Minor planets 10 Hygiea and 175 Andromache with Respect to Perturbations by Jupiter". Proceedings of the National Academy of Sciences of the United States of America. 8 (7): 170–173. Bibcode:1922PNAS....8..170L. doi:10.1073/pnas.8.7.170. PMC 1085085. PMID 16586868.
  14. ^ a b Hind, J. R. (1852). The Solar System: Descriptive Treatise Upon the Sun, Moon, and Planets, Including an Account of All the Recent Discoveries. G. P. Putnam. p. 126. Bibcode:1852ssdt.book.....H.
  15. ^ a b c d Barucci, M. (2002). "10 Hygiea: ISO Infrared Observations". Icarus. 156 (1): 202. Bibcode:2002Icar..156..202B. doi:10.1006/icar.2001.6775.
  16. ^ Bala, Gavin Jared; Miller, Kirk (18 September 2023). "Unicode request for historical asteroid symbols" (PDF). unicode.org. Unicode. Retrieved 26 September 2023.
  17. ^ Unicode. "Proposed New Characters: The Pipeline". unicode.org. The Unicode Consortium. Retrieved 6 November 2023.
  18. ^ Faulks, David (28 May 2016). "L2/16-080: Additional Symbols for Astrology" (PDF). Archived (PDF) from the original on 11 May 2022. Retrieved 22 May 2023.
  19. ^ Gingerich, O. (16 August 2006), "The Path to Defining Planets" (PDF), Harvard-Smithsonian Center for Astrophysics and IAU EC Planet Definition Committee chair, p. 4, archived (PDF) from the original on 25 October 2020, retrieved 13 March 2007
  20. ^ "Asteroids: Structure and composition of asteroids". European Space Agency. Archived from the original on 31 March 2020. Retrieved 30 October 2019.
  21. ^ a b Odeh, M. "The Brightest Asteroids". The Jordanian Astronomical Society. Archived from the original on 11 May 2008. Retrieved 21 May 2008.
  22. ^ "What Can I See Through My Scope?". Ballauer Observatory. 2004. Archived from the original on 22 June 2013. Retrieved 20 July 2008.
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  24. ^ Hilton, J. L. "Asteroid Masses and Densities" (PDF). U.S. Naval Observatory. Lunar and Planetar Institute. Archived from the original (PDF) on 19 August 2008. Retrieved 26 August 2008.
  25. ^ Hanuš, J.; Viikinkoski, M.; Marchis, F.; Ďurech, J.; Kaasalainen, M.; Delbo, M.; Herald, D.; Frappa, E.; Hayamizu, T.; Kerr, S.; Preston, S.; Timerson, B.; Dunham, D.; Talbot, J.; et al. (15 May 2017). "Volumes and bulk densities of forty asteroids from ADAM shape modeling" (PDF). Astronomy & Astrophysics. 601: A114. arXiv:1702.01996. Bibcode:2017A&A...601A.114H. doi:10.1051/0004-6361/201629956. S2CID 119432730. Archived (PDF) from the original on 19 May 2020. Retrieved 28 July 2019.
  26. ^ Storrs, A. D.; Wells, E. N.; Zellner, B. H.; Stern, A.; Durda, D. D.; et al. (1999). "Imaging Observations of Asteroids with HST". Bulletin of the American Astronomical Society. 31: 1089. Bibcode:1999DPS....31.1103S. Archived from the original on 31 October 2019. Retrieved 31 October 2019.
  27. ^ "JPL Close-Approach Data: 10 Hygiea". 27 November 2009. Archived from the original on 29 November 2020. Retrieved 2 March 2010.
  28. ^ L'vov, V. N.; Smekhacheva, R. I.; Smirnov, S. S.; Tsekmejster, S. D. (2007). "Some Peculiarities in the Hildas' Motion" (PDF). Central Astronomical Observatory of Russian Academy of Sciences. 2008. Archived (PDF) from the original on 31 October 2019. Retrieved 30 October 2019.
  29. ^ "Perturbing Bodies". Minor Planet Center. Archived from the original on 16 November 2020. Retrieved 18 April 2013.
  30. ^ a b c Nesvorný, D.; Morbidelli, A. (December 1998). "Three-Body Mean Motion Resonances and the Chaotic Structure of the Asteroid Belt". The Astronomical Journal. 116 (6): 3029–3037. Bibcode:1998AJ....116.3029N. doi:10.1086/300632.
  31. ^ Family status for each asteroid with synthetic proper elements, AstDyS-2, archived from the original on 31 October 2019, retrieved 30 October 2019

External links[edit]