_animation_(cropped).gif) Low-resolutionHubble Space Telescope image of Gonggong and its moonXiangliu, October–December 2017 | |
| Discovery[1][2] | |
|---|---|
| Discovered by | |
| Discovery site | Palomar Obs. |
| Discovery date | 17 July 2007 |
| Designations | |
| (225088) Gonggong | |
| Pronunciation | /ˈɡɒŋɡɒŋ/[3] |
Named after | Gònggōng (共工) |
| |
| TNO[5] · SDO[6] 3:10 res.[7][8] · dwarf planet[9] | |
| Symbol | .svg) [10] |
| Orbital characteristics[1] | |
| Epoch 21 November 2025 (JD 2461000.5) | |
| Uncertainty parameter 3 | |
| Observation arc | 40 years and 37 days (14647 days) |
| Earliestprecovery date | 19 August 1985 |
| Aphelion | 100.555 AU (15.0428 Tm) |
| Perihelion | 33.235 AU (4.9719 Tm) |
| 66.895 AU (10.0073 Tm) | |
| Eccentricity | 0.50318 |
| 547.13yr (199,837 days)[5] | |
| 111.384° | |
| 0° 0m 6.485s / day | |
| Inclination | 30.8664° |
| 336.8401° | |
| 17 February 1857[11] | |
| 206.6442° | |
| Knownsatellites | 1 (Xiangliu) |
| Physical characteristics | |
| 1230±50 km[12]: 1 | |
| 615±25 km | |
| Mass | (1.75±0.07)×1021 kg[12]: 3 |
Meandensity | 1.74±0.16 g/cm3[12]: 4 |
Equatorialsurface gravity | ≈ 0.18 m/s2 |
Equatorialescape velocity | ≈ 0.62 km/s |
| 22.40±0.18 h or44.81±0.37 h (ambiguous,[13][14] but 22.4 h more likely[12]) | |
| 0.14±0.01[12] | |
| B−V=1.38±0.03[15][16] V−R=0.86±0.02[15][16] V−I=1.65±0.028[15][16] | |
| 21.4[17] | |
| 2.34[13] · 2.0[9] 1.84[5][1] | |
Gonggong (minor-planet designation:225088 Gonggong) is adwarf planet and a member of thescattered disc beyondNeptune. It has a highlyeccentric andinclined orbit during which it ranges from 33–101astronomical units (4.9–15.1 billion kilometers; 3.1–9.4 billion miles) from theSun. As of 2019[update], its distance from the Sun is 88 AU (13.2×10^9 km; 8.2×10^9 mi), and it is the sixth-farthest known Solar System object. According to theDeep Ecliptic Survey, Gonggong is in a 3:10orbital resonance with Neptune, in which it completes three orbits around the Sun for every ten orbits completed by Neptune. Gonggong was discovered in July 2007 by American astronomersMegan Schwamb,Michael Brown, andDavid Rabinowitz at thePalomar Observatory, and the discovery was announced in January 2009.
At approximately 1,230 km (760 mi) in diameter, Gonggong is similar in size toPluto's moonCharon, making it thefifth-largest knowntrans-Neptunian object (apart possibly from Charon). It may be sufficiently massive to be inhydrostatic equilibrium and therefore a dwarf planet. Gonggong's large mass makes retention of a tenuousatmosphere ofmethane just possible, though such an atmosphere would slowly escape into space. The object is named afterGònggōng, a Chinese water god responsible for chaos, floods and the tilt of the Earth. The name was chosen by its discoverers in 2019, when they hosted an online poll for the general public to help choose a name for the object, and the name Gonggong won.
Gonggong is red, likely due to the presence oforganic compounds calledtholins on its surface. Waterice is also present on its surface, which hints at a brief period ofcryovolcanic activity in the distant past. With a rotation period of around 22 hours, Gonggong rotates slowly compared to other trans-Neptunian objects, which typically have periods of less than 12 hours. The slow rotation of Gonggong may have been caused bytidal forces from itsnatural satellite, namedXiangliu.
Gonggong was discovered by American astronomersMegan Schwamb,Michael Brown andDavid Rabinowitz on 17 July 2007.[1] The discovery was part of thePalomar Distant Solar System Survey, a survey conducted to find distant objects in the region ofSedna, beyond 50 AU (7.5×109 km; 4.6×109 mi) from theSun, using theSamuel Oschin telescope atPalomar Observatory nearSan Diego,California.[18][19][20] The survey was designed to detect the movements of objects out to at least 1,000 AU from the Sun.[20] Schwamb identified Gonggong by comparing images using theblinking technique.[19] In the discovery images, Gonggong appeared to move slowly, suggesting that it is a distant object.[19][21] The discovery was part of Schwamb'sdoctoral thesis. At that time, Schwamb was a graduate student of Michael Brown at theCalifornia Institute of Technology.[22][19]
Gonggong was formally announced in aMinor Planet Electronic Circular on 7 January 2009.[2] It was then given theprovisional designation2007 OR10 because it was discovered during the second half of July 2007.[2] The last letter and numbers of its designation indicate that it is the 267th object discovered during the latter half of July.[a] As of September 2025[update], it has been observed 484 times over 23oppositions, and has been identified in twoprecovery images, with the earliest image taken by theLa Silla Observatory on 19 August 1985.[1][24]
The object is named afterGònggōng, a water god inChinese mythology. Gonggong is depicted as having a copper-and-iron, red-haired human head (or sometimes torso) and the body or tail of a serpent. Gonggong was responsible for creating chaos and catastrophe, causing flooding and tilting the Earth, until he was sent into exile.[25] Gonggong is often accompanied by his minister,Xiangliu, a nine-headed poisonous snake monster who was also responsible for causing flooding and destruction.[1]
Before its official naming, Gonggong was the largest known unnamed object in the Solar System.[26] Initially after the discovery of Gonggong, Brown nicknamed the object "Snow White" for its presumed white color based on his assumption that it may be a member of the icyHaumea collisional family.[4][27] The nickname also fit because, by that time, Brown's team had discovered seven other large trans-Neptunian objects which were collectively referred to as the "seven dwarfs":[28]Quaoar in 2002,Sedna in 2003,Haumea,Salacia andOrcus in 2004, andMakemake andEris in 2005. However, Gonggong turned out to be very red in color, comparable to Quaoar, so the nickname was dropped.[4][21] On 2 November 2009, two years after its discovery, theMinor Planet Center assigned theminor planet number 225088 to Gonggong.[24]
When Gonggong's discovery was first announced, Brown did not name it, as he considered it to be an unremarkable object, despite its large size.[27][29] In 2011, he declared that he now had enough information to justify naming it, because of the discovery of water ice and the possibility of methane on its surface, which made it noteworthy enough to warrant further study.[22] Following theKepler spacecraft's large revision ofGonggong's size in 2016, Schwamb justified that Gonggong was eligible for naming, an acknowledgement of its large size and that its characteristics were known with enough certainty for a name to be given to reflect them.[26]
In 2019, the discoverers of Gonggong hosted an online poll for the general public to choose between three possible names:Gonggong (Chinese),Holle (German), andVili (Norse). These were selected by the discoverers in accordance with theInternational Astronomical Union's (IAU's) minor planet naming criteria, which state that objects with orbits like that of Gonggong must be given names related tomythological figures that are associated withcreation.[30][31] The three options were chosen because they were associated with water, ice, snow, and the color red—all characteristics of Gonggong—and because they had associated figures that could later provide a name for Gonggong's satellite.[32] The name for Gonggong's satellite was not chosen by the hosts of the naming poll, as this privilege is reserved for its discoverers.[30][25]
Having gained 46 percent of the 280,000 votes, on 29 May 2019, the discovery team announced Gonggong as the winning name.[25] The name was proposed to the IAU'sCommittee on Small Body Nomenclature (CSBN), which is responsible for naming minor planets.[25] The name was accepted by the CSBN and was announced by the Minor Planet Center on 5 February 2020.[33]
Asplanetary symbols are no longer used regularly in astronomy, Gonggong never received a symbol in the astronomical literature. A symbol⟨.svg)
⟩, used mostly among astrologers,[34] is included inUnicode asU+1F77D 🝽GONGGONG.[35] The symbol was designed by Denis Moskowitz, a software engineer in Massachusetts; it combines the Chinese character 共gòng with a snake's tail.[10]
.gif)
.png)
Gonggong orbits the Sun at an average distance of 66.9 AU (1.001×1010 km; 6.22×109 mi), and completes a full orbit in 547 years.[5] The orbit of Gonggong is highly inclined to theecliptic, with anorbital inclination of 30.9 degrees.[5] Its orbit is also highly eccentric, with a measuredorbital eccentricity of 0.50.[5] Due to its highly eccentric orbit, the distance of Gonggong from the Sun varies greatly over the course of its orbit, from 100.6 AU (1.505×1010 km; 9.35×109 mi) ataphelion, its furthest point from the Sun, to around 33.2 AU (4.97×109 km; 3.09×109 mi) atperihelion, its closest point to the Sun.[5][1] Gonggong last reached perihelion in 1857, and is currently moving farther from the Sun, toward its aphelion.[36] Gonggong will reach aphelion by 2134.[17]
The period, inclination and eccentricity of Gonggong's orbit are all rather extreme compared to other large bodies in the Solar System. Amonglikely dwarf planets, its period is the third-longest, at 547 years compared to 561 years forEris and the ca. 11,400 years ofSedna. Its 31° inclination is second, after 44° for Eris, and its 0.50 eccentricity is also (a rather distant) second, after Sedna at 0.85.
TheMinor Planet Center lists it as ascattered disc object for its eccentric and distant orbit.[6] TheDeep Ecliptic Survey shows the orbit of Gonggong to be in a3:10 resonance with Neptune; Gonggong completes three orbits around the Sun for every ten orbits completed by Neptune.[7]
As of 2021[update], Gonggong is about 89 AU (1.33×1010 km; 8.3×109 mi) from the Sun[37] and is moving away at a speed of 1.1 kilometers per second (2,500 miles per hour).[38] It is theeleventh-farthest known Solar System object from the Sun, preceding2021 DR15 (89.5 AU),2014 UZ224 (89.6 AU),2015 TH367 (90.3 AU),2020 FQ40 (92.4 AU),Eris (95.9 AU),2020 FA31 (97.2 AU),2020 FY30 (99.0 AU),2020 BE102 (111.0 AU),2018 VG18 (123.5 AU), and2018 AG37 (~ 132 AU).[37][39][40] Gonggong is more distant thanSedna, which is located 84.3 AU from the Sun as of 2021[update].[37] It has been farther from the Sun than Sedna since 2013, and it will surpass Eris in distance by 2045.[38][41]
Gonggong has an absolute magnitude (H) of 2.34,[15][13] which makes it the seventh-brightest trans-Neptunian object known. It is dimmer thanOrcus (H=2.31; D=917 km)[42] but brighter than Quaoar (H=2.82; D=1,110 km).[43] The Minor Planet Center and theJet Propulsion Laboratory Small-Body Database assume a brighter absolute magnitude of 1.84,[1][5] which would make it the fifth brightest trans-Neptunian object.[44]
Being 88 AU from the Sun, theapparent magnitude of Gonggong is only 21.5,[45] and so it is too dim to be seen fromEarth with thenaked eye.[30][b] Although closer to the Sun than the dwarf planet Eris, Gonggong appears dimmer, as Eris has a higher albedo and an apparent magnitude of 18.8.[47][48]
The surface of Gonggong has analbedo (reflectivity) of 0.14.[12] The surface composition and spectrum of Gonggong is expected to be similar to that ofQuaoar, as both objects are red in color and display signs ofwater ice and possiblymethane in their spectra.[49][47] Thereflectance spectrum of Gonggong was first measured in 2011 atnear-infrared wavelengths, with the Folded port InfraRed Echellette (FIRE)spectrograph on theMagellan Baade Telescope at theLas Campanas Observatory inChile.[50] Gonggong's spectrum exhibits a strong redspectral slope along with broadabsorption bands atwavelengths of 1.5 μm and 2 μm, meaning that Gonggong reflects more light at these wavelengths.[50] Additionalphotometric measurements from theHubble Space Telescope'sWide Field Camera 3 instrument display similar absorption bands at 1.5 μm,[50] which are characteristic features of water ice, a substance often found on largeKuiper belt objects.[51] The presence of water ice on the surface of Gonggong implies a brief period ofcryovolcanism in the distant past, when water erupted from its interior, deposited onto its surface, and subsequently froze.[52]
Gonggong is among the reddest trans-Neptunian objects known, especially in the visible and near-infrared.[50][15] Its red color is unexpected for an object with a substantial amount of water ice on its surface,[52][22] which are typically neutral in color, hence why Gonggong was initially nicknamed "Snow White".[4][27] Gonggong's color implies that methane is present on its surface, although it was not directly detected in the spectrum of Gonggong due to the lowsignal-to-noise ratio of the data.[50] The presence of methane frost would account for its color, as a result of thephotolysis of methane by solar radiation andcosmic rays producing reddishorganic compounds known astholins.[50][13] Observations of Gonggong's near-infrared spectrum in 2015 revealed an absorption feature at 2.27 μm, indicating the presence ofmethanol along with its irradiation products on its surface.[53]
Gonggong is large enough to be able to retain trace amounts ofvolatile methane on its surface,[50] even when at its closest distance to the Sun (33.2 AU),[5] where temperatures are higher than that of Quaoar.[50] In particular, the large size of Gonggong means that it is likely to retain trace amounts of other volatiles, includingammonia,carbon monoxide, and possiblynitrogen, which almost all trans-Neptunian objects lose over the course of their existence.[49][13][26] Like Quaoar, Gonggong is expected to be near the mass limit at which it is able to retain thosevolatile materials on its surface.[49][22]
In 2022, low resolution near-infrared (0.7–5 μm)spectroscopic observations by theJames Webb Space Telescope (JWST) revealed the presence of significant amounts ofethane ice (C2H6) on the surface of Gonggong, though there appears to be less ethane on Gonggong than onSedna. The JWST spectra also contain evidence of presence of small amounts ofcarbon dioxide (CO2) complexed with either dark surface material or some ices as well as complex organics. On the other hand no evidence of presence ofmethane (CH4) andmethanol (CH3OH) was found at variance with the earlier observations.[54]
The presence of tholins on the surface of Gonggong implies the possible existence of methane ice on the surface and a tenuous methane atmosphere analogous to Quaoar.[52][22] Gonggong occasionally comes closer to the Sun than Quaoar, where it becomes warm enough for the methane ice on the surface to sublimate, possibly creating an atmosphere. Gonggong's larger mass makes the retention of methane just possible.[50] During aphelion, methane along with othervolatiles would condense on Gonggong's surface, allowing for long-term irradiation that would otherwise result in a decrease in surface albedo.[55] The lower surface albedo would contribute to the loss of highly volatile materials such as nitrogen, as a lower albedo corresponds to more light beingabsorbed by the surface rather than being reflected, thus resulting in greater surface heating. Hence, the nitrogen content of Gonggong's atmosphere is expected to be depleted to trace amounts while methane is likely retained.[55]
Gonggong is thought to have had cryovolcanic activity along with a more substantial atmosphere shortly after itsformation.[52][22] Such cryovolcanic activity is expected to have been brief, and the resulting atmosphere graduallyescaped over time.[52][22] Volatile gases, such as nitrogen and carbon monoxide, were lost, while less volatile gases such as methane are likely to remain in its present tenuous atmosphere.[52][55]
| Year | Diameter | Method | Refs |
|---|---|---|---|
| 2010 | 1,752 km | thermal | [56] |
| 2011 | 1,200+300 −200 km | best fit albedo | [50] |
| 2012 | 1,280±210 km | thermal | [47] |
| 2013 | 1,142+647 −467 km | thermal | [57] |
| 2013 | 1,290 km | radiometric | [9] |
| 2016 | 1,535+75 −225 km | thermal | [13] |
| 2018 | 1,230±50 km | radiometric | [12] |
As of 2019, Gonggong is estimated to have a diameter of 1,230 km (760 mi), derived fromradiometric measurements, its calculated mass, and assuming a density similar to other similar bodies.[12] This would make Gonggong the fifth-largest trans-Neptunian object, afterPluto,Eris,Haumea andMakemake. Gonggong is approximately the size of Pluto's moonCharon, although Gonggong's current size estimate has an uncertainty of 50 km (31 mi).[12]
Gonggong has been classified as a dwarf planet by several astronomers.[56][58][9] Brown states that Gonggong "must be a dwarf planet even if predominantly rocky", based on the 2013 radiometric measurement of 1,290 km (800 mi).[9]Scott Sheppard and colleagues think that it is likely to be a dwarf planet,[58] based on its minimum possible diameter—580 km (360 mi) under the assumption of a completely reflective surface with an albedo of 1[c]—and what was at the time the expected lower size limit of around 200 km (120 mi) forhydrostatic equilibrium in cold icy-rocky bodies.[58] However,Iapetus is not in equilibrium despite being 1,470 km (910 mi) in diameter, so this remains just a possibility.[60]
In 2010, astronomerGonzalo Tancredi initially estimated Gonggong to have a very large diameter of 1,752 km (1,089 mi), though its dwarf planet status was unclear as there was no lightcurve data or other information to ascertain its size.[56] Gonggong is too distant to be resolved directly; Brown placed a rough estimate of its diameter ranging from 1,000–1,500 km (620–930 mi), based on an albedo of 0.18 which was the best fit in his model.[50] A survey led by a team of astronomers using theEuropean Space Agency'sHerschel Space Observatory in 2012 determined its diameter to be1280±210 km (795±130 mi), based on the thermal properties of Gonggong observed in thefar infrared range.[47] This measurement is consistent with Brown's estimate. Later observations in 2013 using combined thermal emission data fromHerschel and theSpitzer Space Telescope suggested a smaller size of1142+647
−467 km (710+402
−290 mi), though this estimate had a larger range of uncertainty.[57]
In 2016, combined observations from theKepler spacecraft and archival thermal emission data fromHerschel suggested that Gonggong was much larger than previously thought, giving a size estimate of1535+75
−225 km (954+46
−140 mi) based on an assumed equator-on view and a lower estimated albedo of 0.089.[13][14] This would have made Gonggong the third-largest trans-Neptunian object after Eris and Pluto, larger than Makemake (1,430 km (890 mi)).[14][26] These observations of Gonggong were part of theKepler spacecraft'sK2 mission which includes studyingsmall Solar System bodies.[26] Subsequent measurements in 2018 revised the size of Gonggong to1230±50 km (764±31 mi), based on the mass and density of Gonggong derived from the orbit of its satellite and the discovery that the viewing direction was almostpole-on.[12] With this size estimate, Gonggong is again thought to be the fifth-largest trans-Neptunian object.[12]
Based on the orbit of its satellite, the mass of Gonggong has been calculated to be 1.75×1021 kg (3.86×1021 lb), with a density of1.74±0.16 g/cm3.[12] Given the mass, the 2016 size estimate of 1,535 km (954 mi) would have implied an unexpectedly low (and likely erroneous) density of0.92 g/cm3.[12]
Gonggong is the fifth most massive trans-Neptunian object, after Eris, Pluto, Haumea, and Makemake.[12] It is slightly more massive and denser than Charon, which has a mass of 1.586×1021 kg (3.497×1021 lb) and a density of1.702 g/cm3.[12][61] Due to its large size, mass, and density, Gonggong is expected to be in hydrostatic equilibrium, taking the shape of aMacLaurin spheroid that is slightlyflattened due to its rotation.[12][13]
The rotation period of Gonggong was first measured in March 2016, through observations of variations in its brightness with theKepler space telescope.[13] Gonggong's light curveamplitude as observed byKepler is small, only varying in brightness by about 0.09magnitudes.[13] The smalllight curve amplitude of Gonggong indicates that it is being viewed at a pole-on configuration, further evidenced by the observed inclined orbit of its satellite.[12] TheKepler observations provided ambiguous values of44.81±0.37 and22.4±0.18 hours for the rotation period.[13][12] Based on a best-fit model for its rotation pole orientation, the value of22.4±0.18 hours is thought to be the more plausible one.[12] Gonggong rotates slowly compared to other trans-Neptunian objects, which usually have periods between 6 and 12 hours.[12] Due to its slow rotation, it is expected to have a lowoblateness of 0.03 or 0.007, for rotation periods of 22.4 or 44.81 hours, respectively.[12]
.jpg)
Following the March 2016 discovery that Gonggong was an unusually slow rotator, the possibility was raised that a satellite may have slowed it down viatidal forces.[62] The indications of a possible satellite orbiting Gonggong led Csaba Kiss and his team to analyzearchival Hubble observations of Gonggong.[63] Their analysis of Hubble images taken on 18 September 2010 revealed a faint satellite orbiting Gonggong at a distance of at least 15,000 km (9,300 mi).[64] The discovery was announced in aDivision for Planetary Sciences meeting on 17 October 2016.[30] The satellite is approximately 100 km (62 mi) in diameter and has an orbital period of 25 days.[63] On 5 February 2020 the satellite was officially namedXiangliu, after the nine-headed poisonous snake monster that accompanied Gonggong in Chinese mythology. This naming came at the same time that Gonggong itself was officially named.[1]
It was calculated byplanetary scientistAmanda Zangari that aflyby mission to Gonggong would take a minimum of over 20 years with current rocket capabilities.[65] A flyby mission could take just under 25 years using a Jupitergravity assist, based on a launch date of 2030 or 2031. Gonggong would be approximately 95 AU from the Sun when the spacecraft arrives.[65]
Objects with distance from Sun over 84.2 AU
| Consensus | _(cropped).jpg)  | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Candidate (for TNOs, D+1σ ≥ 700 km or H ≤ 4.0) |
| ||||||||||||
_and_Eris_orbits%2c_Jan2018%2c_top_view.png)
_and_Eris_orbits%2c_Jan2018%2c_side_view.png)
