Hygiea has a nearly spherical shape, with two knowncraters about 100 and 180 km (62 and 112 mi) in diameter. Because of its shape and large size, some researchers consider Hygiea apossible dwarf planet. Hygiea has a dark,carbonaceous surface consisting ofhydrated andammoniatedsilicate minerals, withcarbonates and water ice. Hygiea's subsurface likely contains a large fraction of water ice. These characteristics make Hygiea very similar to the main-beltdwarf planetCeres, which suggests the two objects have similar origins and evolutionary histories.[12]: 2
Hygiea is theparent body of theHygiea family, anasteroid family comprising over 7,000 known asteroids that share similar orbital and compositional characteristics with Hygiea.[13] The Hygiea family is believed to have formed by a giant impact on Hygiea about 2 to 3 billion years ago.[14] This impact is thought to have shattered Hygiea, which led to its reaccumulation as a nearly spherical body.
Annibale de Gasparis discovered Hygiea on 12 April 1849.
Hygiea was discovered on the evening of 12 April 1849 by Italian astronomerAnnibale de Gasparis at theAstronomical Observatory of Capodimonte inNaples, Italy.[15]: XV [16]: 10 On that night he was using the observatory's Reichenbachequatorial telescope[17][b] to observe a section of the sky in the 12thhour ofright ascension, as part of his larger project ofcataloguing stars along theecliptic up to the 14thapparent magnitude.[15]: XV–XVI [16]: 10 While comparing his observations to theBerlin Academy'sstar chart,[16]: 10 [c] de Gasparis noticed a starlike object between magnitude 9 and 10 which was not recorded before.[20]: 126 [16]: 10 [d] Although poor weather prevented further observations for a few days, de Gasparis reobserved the object on 14 and 17 April and confirmed it had moved between these dates.[20]: 126 [19] Judging by how much the object had moved, de Gasparis concluded it must be another newplanet[e] between the orbit ofMars andJupiter.[20]: 126 De Gasparis announced his discovery to Erasmo Fabri Scarpellini,[23]: 28 secretary of theCorrespondenza Scientifica bulletin atRome, Italy,[20]: 126 who in turn passed on the news toHeinrich Christian Schumacher, who published it in theAstronomische Nachrichten journal on 11 May 1849.[19][22] Hygiea was the first asteroid discovered by de Gasparis and the tenth asteroid discovered in history.[22][24]: 80 He would later discover another six asteroids between 1850 and 1853 and two more during the 1860s.[22]
De Gasparis invitedErnesto Capocci Belmonte, his friend and director of the Capodimonte Observatory, to assign a name to the asteroid as gratitude for his help and advice.[15]: XVI [16]: 10 Capocci suggested the nameIgea—the Italian spelling ofHygieia, theGreek goddess of health and daughter ofAsclepius.[17][16]: 10 De Gasparis added the adjectiveBorbonica to Capocci's suggested name, to honorKing Ferdinand II of theBourbons of Naples who ruled theKingdom of the Two Sicilies and supported the work of the Capodimonte Observatory.[25][15]: XVI Together, de Gasparis and Capocci proposed the nameIgea Borbonica ("Bourbon Hygieia") in a letter forwarded to Ferdinand II on 8 May 1849.[26][16]: 10 De Gasparis's commemoration of the Bourbons may have helped him and Capocci circumvent punishment for their participation in theliberal movements of 1848.[27]
The nameIgea Borbonica was not mentioned in the first communications to the European scientific community.[16]: 10 When English astronomerJohn Herschel received the news of Hygiea's discovery from hisNeapolitan colleagues,[16]: 10 he suggested thatParthenope would be an apt name for de Gasparis's discovery, as it comes from the siren who founded Naples in Greek mythology.[22][20]: 127 In a letter written to English mathematicianAugustus De Morgan in April 1849, Herschel wrote:
No name has yet been mentioned. What do you think of Parthenope (being a Neapolitan?) I should think it will occur as a matter of course to Gasparis if he has any classical reading.
— John Herschel, in a letter to Augustus De Morgan (April 1849)[17][16]: 10–11
Herschel corresponded with other European scientists and astronomers to hear their thoughts on the name Parthenope for de Gasparis's discovery, although by the time he reached out to de Gasparis, Hygiea had already been named one month earlier.[17] When Schumacher, editor ofAstronomische Nachrichten, learned of the name proposed by de Gasparis and Capocci, he complained in a letter addressed to Herschel on 26 June 1849 that it had the Italian spelling instead of the Latin form, as conventionally done for all the other planets.[17] Regardless, de Gasparis recognized Herschel's suggestion and expressed desire to realize Herschel's wish.[17][20]: 167 On 11 May 1850, de Gasparis discovered the asteroid11 Parthenope and acknowledged Herschel for the name in his announcement.[22]
There are multiple variations on the Latin spelling of Hygiea, includingHygièa,Hygia, andHygea.[17][28] The modern English formHygiea is a less common variant of the name of the goddess, which in Greek is Ὑγίεια (Hygieia)[29] or Ὑγεῖα (Hygeia).[30] The name was often spelledHygeia (and occasionallyHygea[31][24]: 80 ) by astronomers during the early 1850s, though by the 1860s, the spellingHygiea became commonplace.[32] According to the English astronomerJohn Russell Hind, the adjectiveBorbonica had been dropped by 1852.[20]: 126 [33]: 68–70
As with the other previously discovered asteroids, Hygiea was given anastronomical symbol as a way of representing it. The symbol for Hygiea was proposed by de Gasparis in a letter addressed to Hind on 4 November 1850, in which he wrote, "The symbol of Hygeia [sic] is a serpent (like a Greekζ) crowned with a star."[34] Visually, de Gasparis's symbol for Hygiea is depicted as: (U+1F779 inUnicode 17.0).[35]: 7 [36] The serpent, particularly whendrinking from a bowl, is a traditional symbol of the goddess Hygieia (cf. U+1F54F 🕏).[37]
Both symbols of Hygiea soon became obsolete, as the number of asteroids discovered had grown too much for each to have unique symbols.[38][24]: 80 In 1851Johann Franz Encke proposed a different identification system, suggesting using a number corresponding to the order of discovery enclosed in a small circle[38][35]: 5 —for Hygiea it would be ⑩.[24]: 80 Astronomers began adopting Encke's circled number scheme in scientific publications, though as the number of asteroids discovered grew, astronomers eventually switched to enclosing the number inparentheses, which became the modernminor-planet designation scheme.[38][35]: 5 In the case of Hygiea, its modern minor planet designation would be(10) Hygiea[10] or10 Hygiea.[1]
TheMinor Planet Center uses theminor planet provisional designationsA849 GA andA900 GA for Hygiea,[10] though these are only retrospective extensions of the new-style provisional designation scheme established in 1925.[39] While the provisional designation A849 GA refers to the discovery date of Hygiea, the designation A900 GA refers to the date when Hygiea was serendipitously observed and catalogued (asArequipa 38[40]: 13 ) by theHarvard College Observatory's photographicsky survey atArequipa, Peru in 1900.[41][10][f]
Hygiea has seen some minorastrological use, though its symbol was confused once again, with Asclepsius's rod replaced byMercury'scaduceus:, though in a more elaborate form (U+2BDA ⯚) than the caduceus symbol of the planet Mercury.[35]: 6 [42]: 11 The caduceus has long been mistaken for the rod of Asclepius (seecaduceus as a symbol of medicine).
While the first four asteroids discovered—Ceres (1801),Pallas (1802),Juno (1804), andVesta (1807)—were considered planets during the first half of the 19th century (with some astronomers continuing to consider them as such until the end of the century), the discovery of Hygiea occurred when the classification of asteroids was already evolving.[38] Hygiea was referred to as aplanet in the following years after its discovery,[17] though by 1852 astronomers have also called Hygiea aminor planet[20]: 127 or anasteroid.[24]: 80 These terms were introduced prior to Hygiea's discovery and became more used with the discovery of more asteroids beginning in the 1850s.[38] From the second half of the 19th century, asteroids began to be treated in a predominantly collective way, grouped according to orbital or spectral characteristics, with less attention to the individual object.[44]
In 2006, theInternational Astronomical Union's (IAU) committee fordrafting a new definition of planet had considered classifying Hygiea among the planets or the newly-coined category ofdwarf planets, if it were found that the asteroid is massive enough to be shaped predominantly byhydrostatic equilibrium.[45]: 238 [43]: 17 [46]: 50 This proposal for the definition of planet has since been revised and adopted to decree that a planet must orbit the Sun, have sufficient mass to attain a spherical shape by hydrostatic equilibrium, andclear its neighbourhood; objects that satisfy all but the last criterion are considered dwarf planets.[47][6]: 137–138 Since 2019, telescope images have resolved Hygiea's nearly spherical shape, suggesting that it may have reached hydrostatic equilibrium.[13] Because Hygiea already orbits the Sun and is located in the asteroid belt where it has not cleared its orbital neighborhood, Hygiea's nearly spherical shape could qualify it as a dwarf planet, according to Pierre Vernazza and collaborators who studied Hygiea with telescope imaging.[47][6]: 138–139 [13] If so, Hygiea could be the smallest dwarf planet known.[13][48] However, the IAU has not yet officially classified Hygiea as a dwarf planet.[12]: 1
Hygiea is in athree-body mean motion orbital resonance with Jupiter andSaturn.[52]: 3032 In this resonance, themean motions or orbital frequencies of Jupiter, Saturn, and Hygiea follow the relation, where alinear combination of their mean motions () withinteger coefficients equals zero.[52]: 3032 [53]: 78 Simulations show that this three-body resonance leads to achaotic evolution in Hygiea's orbit, with a short[52]: 3029 Lyapunov time between 14,000[4] and 16,000 years.[53]: 78 This means that changes in Hygiea's orbit become exponentially less predictable over this time scale.[52]: 3029
Other asteroids occasionally pass close to Hygiea, sometimes close enough that their trajectories become visiblyperturbed or deflected by Hygiea's gravity.[54]: 311 [55]: 29 This allows astronomers to measure Hygiea's mass.[54]: 311 A 2002 study identified 40 known asteroids that have passed within 0.05 AU (7.5 million km; 4.6 million mi) of Hygiea between 1970 and 2000.[56]: 1118 Over a time span of 30 million years, Hygiea's gravitational perturbations can cause theproper semi-major axes of close-passing asteroids to change by 0.000908 AU (136,000 km; 84,400 mi).[57]: 5
This sectionneeds expansion. You can help byadding to it.(March 2025)
Hygiea is theparent body of theHygiea family, anasteroid family comprising over 7,000 known asteroids that share similar orbital and compositional characteristics with Hygiea.[13] The Hygiea family is the most populous asteroid family in the outer main belt,[51] and is believed to have formed by a giant impact on Hygiea that ejected at least 1.7% of the asteroid's original mass[6] about 2 to 3 billion years ago.[14] The impactor that formed the Hygiea family was probably between 75 and 150 km (47 and 93 mi) in diameter.[6] Hygiea contains almost all the mass (over 98%) of the family.[6]
Rotational light curve of Hygiea measured by theTRAPPIST telescope in 2018
Simulation of Hygiea's retrograde (clockwise) rotation
Therotation period of Hygiea is about 13.83hours (13 hours and 49.5 minutes), with an uncertainty of 0.2 seconds.[6]: 136 [5]: 18 This rotation period was determined via direct imaging and analysis of Hygiea'slight curve, or changes in brightness over time.[58][6]: 139 From Earth, Hygiea's brightness periodically fluctuates by up to 15% from its average value[59]: 3 asalbedo features on Hygiea's surface rotate in and out of view.[58] The north pole of Hygiea's rotation axis points toward the ecliptic south, in the direction ofecliptic longitude306°±3° and ecliptic latitude−29°±3°.[5]: 18 This means Hygiea's rotation axis is highly tilted with anobliquity of 120° with respect to the ecliptic.[5]: 18 Since Hygiea's obliquity is greater than 90°, it has aretrograde rotation, meaning it rotates backwards with respect to the direction of its orbit around the Sun.[60]: 54
Before it was directly imaged by telescopes in 2017–2018, Hygiea was thought to have a rotation period twice as long as the currently accepted value.[58][6]: 139 The first measurements of Hygiea's rotation period beginning in the 1950s reported 18 hours[61]: 538–539 [60]: 53 while studies from 1991 and onward reported 27.6 hours.[6]: 139 These past observations did not collect enough datapoints to produce reliable light curves, which led to these inaccurate rotation period measurements.[58][6]: 139
Relative sizes of the four largest asteroids. Hygiea is furthest right.
Hygiea is thefourth-largest main-belt asteroid by both volume and mass, with a volume-equivalentmean diameter of 433 ± 8 km (269 ± 5 mi) and a mass of(8.74±0.69)×1019 kg.[g] Compared to the largest asteroid Ceres, Hygiea is less than half its diameter and is roughly 10% as massive.[12]: 15 Hygiea constitutes 3% of the total mass of the entire main belt[62]: 736 and is the largest asteroid in the outer main belt.[49]: 18 The four largest asteroids (Ceres, Pallas, Vesta, and Hygiea) together make up a little more than half of the entire main belt's mass.[62]: 738 These four largest asteroids have sometimes been collectively referred to as the "Big Four" by astronomers,[63][56] although historically this term meant the first four asteroids discovered (Ceres, Pallas, Juno, and Vesta).[64]: 26 Hygiea was not recognized as the fourth-largest asteroid until 1974, whenDavid Morrison measured its diameter andalbedo for the first time by using itsinfraredthermal emission.[65]: 211
The best estimate for Hygiea's diameter was measured via direct imaging using theVery Large Telescope (VLT) inChile, whoseatmospheric turbulence-correctingadaptive optics could resolve the asteroid in highangular resolution.[13][5]: 1 Hygiea's mass was measured by observing how its gravity deflects the paths of other asteroids that pass near it.[59]: 18–19 This requires an extensive number of observations with accurate positional measurements of the deflected asteroid before and after its close approach.[66]: 1 [54]: 311 The measurement of Hygiea's mass through this method was first attempted in 1986, with the analysis of a past close approach by the asteroid829 Academia (which passed 0.006 AU or 900 thousand km or 560 thousand mi from Hygiea on 19 May 1927[67]: 705 ).[54]: 311–313 Hygiea's mass has since been refined with additional asteroid close approaches and more accurate observations.[67]: 705 [59]: 18–19
The nearly spherical shape model of Hygiea as seen from three mutually orthogonal viewsHygiea's two large craters "Serpens" and "Calix" identified in VLT images from 2017. A bright spot is also present near Calix.
Hygiea is a nearly spherical orellipsoidal object[47][6]: 137 whose diametric dimensions are 450 km × 430 km × 424 km (280 mi × 267 mi × 263 mi), with an uncertainty of ±10 km (6.2 mi) for the equatorial axes and ±20 km (12 mi) for the polar axis.[6]: 136 It is the second-most spherical main-belt asteroid after Ceres.[5]: 5 The nearly spherical shape of Hygiea suggests it may be inhydrostatic equilibrium, having attained its shape by its own gravity.[6]: 138 Specifically, Hygiea's polarflattening andspecific angular momentum closely matches that of aMaclaurin spheroid, which is the shape assumed by a rotating self-gravitating fluid in hydrostatic equilibrium.[6]: 137 [5]: 7
In contrast to the larger asteroid Vesta, Hygiea lacks largeimpact craters orbasins that would otherwise deform its shape from a sphere.[6]: 137 Only two craters on Hygiea have been confidently identified in VLT imaging, with their respective diameters being 180 ± 15 km (111.8 ± 9.3 mi) and 97 ± 10 km (60.3 ± 6.2 mi).[6]: 139 [59]: 11 Both craters appear to havecentral peaks.[59]: 11 Vernazza and collaborators who studied these images have informally named the larger crater "Serpens" and smaller crater "Calix", after the Latin words for 'snake' and 'cup', respectively.[47][59]: 11 These names, which are not approved by the IAU, were chosen because theireponyms commonly appear in symbols of Hygiea.[59]: 11
Besides Serpens and Calix, VLT images of Hygiea show no obvious or bowl-shaped craters larger than 30 km (19 mi) in diameter.[6]: 139 Ceres similarly lacks large bowl-shaped craters and is instead dominated by flat-flooredcomplex craters, which are difficult to see from Earth—this may be the case for Hygiea.[6]: 139 [5]: 9 An abundance of flat-floored craters on Hygiea could indicate a water ice-rich subsurface, which would allow for the relaxation of its surface topography.[6]: 139
Although Hygiea lacks major impact basins, the existence of the Hygiea family points to a majorcollisional event in its past.[13] Rather than leaving a giant impact basin like on Vesta, the impact is thought to have completely shattered Hygiea, which erased all of its pre-existing surface features.[47][6]: 137 Simulations of the giant impact show that most of Hygiea's debris reaccumulated into an oscillating fluid-like body, which was able to relax into a sphere by its own gravity.[48][6]: 137–138 The present-day ellipsoidal shape of Hygiea suggests it solidified around four hours after the impact.[6]: 137 [59]: 8 Other large asteroids that are parents of asteroid families, such as8 Flora and31 Euphrosyne, have also been found to show roughly spherical shapes and are thus believed to have undergone similar collisional disruption and reaccumulation.[5]: 5
Albedo and shadow map of Hygiea's southern hemisphere in anequirectangular projection, constructed from VLT images.[6]: 139 [59]: 10 A bright spot is present at longitude290° and latitude−30°.[6]: 139
The surface of Hygiea is dark,[68]: 1 with an averagevisualgeometric albedo estimated between 6.3% and 7.2%.[5]: 6 [6]: 139 The apparent brightness orreflectance varies across Hygiea's surface due to variations inalbedo and shadows cast by topographic features.[6]: 139 VLT images of Hygiea show several bright spots on its surface, with the brightest one located on Hygiea's southern hemisphere at longitude290° and latitude−30°.[6]: 139 This bright spot is 10% brighter than the average reflectance of Hygiea's surface.[6]: 139 A large dark region is present along Hygiea's equator at longitude60° and latitude0°, though it is most likely a shadowed region.[6]: 139 The albedo and reflectance variation across Hygiea's surface resembles those of Ceres.[6]: 139
The temperature on Hygiea's surface depends on the asteroid's rotation, distance from the Sun,[7]: 336 and the properties of its surfaceregolith.[69]: 194 While the surface of Hygiea have been observed to reach temperatures as high as 230 K (−43 °C; −46 °F) at thesubsolar point,[8]: 204 [9]: 394 the surface cools down it rotates away from the Sun, which averages out the temperature.[69]: 196 Between Hygiea's perihelion and aphelion distances, the average temperature can range from 150 to 180 K (−123 to −93 °C; −190 to −136 °F).[70]: 434 At Hygiea's semi-major axis, the average temperature would be 163 K (−110 °C; −166 °F).[7]: 336
Hygiea has been described as a "fairly dusty object",[69]: 199 [50]: 120 with a regolith layer consisting mostly of fine dust rather than coarse rock.[7]: 335 This fine regolith has a lowthermal inertia, meaning it radiates away heat more easily and leads to cooler temperatures on Hygiea's surface.[69]: 194–195 The regolith of Hygiea may be dustier (and thus finer[71]: 4 ) thanthat of Earth's Moon, which could imply a more mature regolith[69]: 199 that has experienced morespace weathering.[71]: 4 The regolith layer of Hygiea is at least 8 cm (3.1 in) deep.[7]: 335 [8]: 203 These properties of Hygiea's regolith were inferred from the asteroid's lower-than-expected temperature andthermal emission in infrared,submillimetre, andmicrowavewavelengths.[69]: 195 [7]: 335
The similar spectra of Ceres (red) and Hygiea (blue) in visible to near-infraredwavelengths indicate they have similar compositions. Both spectra show absorption signatures of hydrated and ammoniated phyllosilicates.
The spectrum and composition of Hygiea's surface is very similar to those ofcarbonaceous chondritemeteorites and Ceres,[12]: 1 which has led some astronomers to call Hygiea a "primitive" object[8]: 209 and a "virtualspectral twin of Ceres".[12]: 2 Hygiea's resemblance to carbonaceous chondrites (particularlyCM chondrites[12]: 1 ) suggests it shares a similar history of having undergone little thermal alteration and some aqueous alteration of its original minerals, hence its likely primitive nature.[8]: 209 Slight differences between the near-infrared spectra of Hygiea and Ceres indicate they have slightly different concentrations of hydrated and ammoniated minerals.[73]: 9 [12]: 12 High resolution near-infrared spectroscopy by theJames Webb Space Telescope has found that Hygiea's phyllosilicates aremagnesium-rich[12]: 5, 15 and appear to match ammoniatedsaponite.[12]: 12
Ground-based observations have shown that the near-infrared spectrum of Hygiea varies over time, which implies there is compositional variation across Hygiea's surface.[72]: 9 [74]: 18 A 2011 study by Vladimir Busarev observed Hygiea's spectral type changing between C,B, andF over the course of its rotation,[75]: 47–48 which he interpreted as an indication of local dehydration of Hygiea's surface material,[75]: 50 [74]: 18 possibly as a result of heating by impacts.[76]: 15 A 2019 study by Andrew Rivkin and colleagues reported changes in the3.1 μmabsorption feature in Hygiea's near-infrared spectrum over a time scale of years.[77]: 1401 While this absorption feature is often attributed to ammoniated minerals,[77]: 1394, 1403 its variations could also correspond to either hydrated minerals or potentially water ice frost.[77]: 1394, 1401 [72]: 9 Rivkin and colleagues speculated that the variations could be caused by exposed subsurface material on some parts of Hygiea's surface,[77]: 1405 although they do not appear to be correlated with one particular surface location.[77]: 1403
Hygiea'sbulk density has been estimated as either1.944±0.250 g/cm3 or2.06±0.20 g/cm3, based on measurements of its diameter and mass from 2020 and 2021, respectively.[6]: 136–137 [5]: 6 Hygiea's bulk density is similar to that of Ceres (2.16 g/cm3),[6]: 137 which together with Hygiea's large size suggests it could have adifferentiated interior.[72]: 7, 9 [78]: 10 Hygiea likely has a water ice-rich subsurface, as hinted by Hygiea's bulk density, spectroscopic detections of water ice, and its lack of large, bowl-shaped craters.[6]: 139 [79]: 7 Assuming the higher density estimate of2.06±0.20 g/cm3, Hygiea would be among the denser members of the largest C-type asteroids (diameters larger than 300 km or 190 mi), whose densities range between1.5 to 2.16 g/cm3 and may have negligible interiormacroporosities, according to Vernazza and colleagues.[5]: 12 They further speculated that the higher densities of Hygiea and other large C-type asteroids may be due to a morelithified or compacted interior, as a result of significant aqueous alteration.[5]: 12
This sectionneeds expansion. You can help byadding to it.(March 2025)
Despite its size, Hygiea appears very dim when observed fromEarth. This is due to its dark surface and its position in theouter main belt. For this reason, six smaller asteroids were observed beforeAnnibale de Gasparis discovered Hygiea on 12 April 1849.
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 only13 Egeria and17 Thetis having lower mean oppositionmagnitudes.[80] At most oppositions, Hygiea has amagnitude of around +10.2,[80] which is as much as four orders fainter than Vesta, and observation calls for at least a 4-inch (100 mm)telescope to resolve.[81] However, at a perihelic opposition, Hygiea can reach +9.1 magnitude and may just be resolvable with 10 × 50binoculars, unlike the next two largest asteroids in the asteroid belt,704 Interamnia and511 Davida, which are always beyond binocular visibility.[82]
A total of 17stellaroccultations by Hygiea have been tracked by Earth-based astronomers,[83][84] 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.[78] TheHubble 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.[85]
Hygiea has not been explored by anyspace probe. In 2006, Mark V. Sykes and others from thePlanetary Science Institute proposed theExploring the Very Earliest Epoch (EVE) mission toNASA, as part of theDiscovery Program. The proposal, which did not get approved, suggested launching a copy of theDawn probe to Hygiea in October 2011 and arriving to the asteroid viarendezvous in 2021.[68]: 1–2 In 2013,[86]: 431 Pierre Vernazza and Philippe Lamy proposed themedium-class missionINSIDER for theEuropean Space Agency'sSpace Programme.[87] The proposal, which also did not get approved, suggested rendezvousing and orbiting around two or three large main-belt asteroids before releasing one or twolanders. Hygiea and24 Themis were among the potential targets of theINSIDER mission concept.[87] The exploration of primitive main-belt asteroids like Hygiea could provide clues to the processes that led to theformation of the solar system.[87][68]: 1
^Flattening derived from the maximum aspect ratio (c/a):, where (c/a) =0.94±0.05.[5]: 6
^The Reichenbach equatorial telescope was the smaller of the Capodimonte Observatory's twoequatorial telescopes, with anobjectivelens diameter of 8.3 cm (3.3 in) andfocal length of 120 cm (47 in).[16]: 9 The Reichenbach equatorial telescope was located in the northern dome of the observatory.[16]: 10
^The Berlin Academy star chart, which was published in years between 1830 and 1859, was compiled by a collaboration of astronomers who were each allotted a section of the sky spanning one hour of right ascension.[18]: 367 The stars in the 12th (XXII) hour of right ascension were charted byCarl August von Steinheil,[18]: 368 whose map aided de Gasparis's discovery of Hygiea.[19][20]: 126 [15]: XVI
^Hygiea was located at the 12th hour ofright ascension in the sky at the time of its discovery.[21]
^Asteroids were referred to as "planets" at the time of Hygiea's discovery. These would eventually be recategorized as "minor planets".[22]
^In thenew-style provisional designation scheme for pre-1925 minor planet discoveries, the designation begins with the letter A followed by three digits corresponding to the year of discovery ("A849" for 1849, and "A900" for 1900) and ends with two letters, with the first indicating the discovery date's half-month ("G" for the first half of April) and the second indicating the order of discovery in that half-month ("A" meaning first minor planet discovered in that half-month).[39]
^These diameter and mass values come from Vernazza et al. (2021).[5]: 6 In an earlier paper from 2020, the same authors measured a diameter of434±14 km and a mass of(8.32±0.80)×1019 kg.[6]: 136
^abcdede Ritis, Vincenzo (1852). "Cenno de' lavori accademici e dell'azione governativa ne' reali domini continentali dal 1848 al primo semestre del 1852". In Murena, Salvatore (ed.).Annali Civili del Regno delle Due Sicilie (in Italian). Vol. 46. Naples, Italy: Tipografia del Real ministero degli affari interni. pp. XIII–XXI.Archived from the original on 27 November 2024.
^Leuschner, Armin Otto (1922)."(10) Hygiea".Celestial mechanics. A survey of the status of the determination of the general perturbations of the minor planets. Washington, D. C., United States: National Research Council of the National Academy of Sciences. p. 94.
^de Gasparis, Annibale (8 May 1849)."Lettera a Ernesto Capocci" (in Italian). Letter to Capocci, Ernesto. Ministero Pubblica Istruzione. F. 428, f. 3: Archivio di Stato di Napoli. Retrieved27 March 2025.{{cite press release}}: CS1 maint: location (link)
^Lewis, Charlton T.; Short, Charles."Hygēa or Hygīa (Hygĭeia)".A Latin Dictionary. Perseus Digital Library.Archived from the original on 12 May 2024. Retrieved28 March 2025.
^Liddell, Henry George; Scott, Robert."Ὑγίεια".A Greek-English Lexicon. Perseus Digital Library.Archived from the original on 5 December 2022. Retrieved28 March 2025.
^Liddell, Henry George; Scott, Robert."ὑγεῖα".A Greek-English Lexicon. Perseus Digital Library.Archived from the original on 5 December 2022. Retrieved28 March 2025.
^Christensen, Lars Lindberg; Sim, Helen; Shida, Raquel Yumi; Wolf, Nadja; Nielsen, Lars Holm (2006)."The public communication at the IAU GA 2006"(PDF).IAU XXVIth General Assembly.26. International Astronomical Union: 50. Archived fromthe original(PDF) on 1 May 2013. Retrieved29 March 2025.
^abMothé-Diniz, Thais; di Martino, Mario; Bendjoya, Philippe; Doressoundiram, Alain; Fabbio, Migliorini (July 2001). "Rotationally Resolved Spectra of 10 Hygiea and a Spectroscopic Study of the Hygiea Family".Icarus.152 (1):117–126.Bibcode:2001Icar..152..117M.doi:10.1006/icar.2001.6618.S2CID120971986.
^Hilton, J. L."Asteroid Masses and Densities"(PDF).U.S. Naval Observatory. Lunar and Planetar Institute. Archived fromthe original(PDF) on 19 August 2008. Retrieved26 August 2008.
^Ulivi, Paolo; Harland, David M. (2014). "12. The future. Main belt asteroids, Hildas, Trojans, and Centaurs.".Robotic Exploration of the Solar System: Part 4: The Modern Era 2004–2013. Springer. p. 431.ISBN978-1-4614-4812-9.
.svg)
.svg)
.svg)
.svg)
.svg)
![[icon]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aWiki_letter_w_cropped.svg)
_(cropped).jpg)
