225088 Gonggong
Synodic rotation period | 22.40±0.18 h or 44.81±0.37 h (ambiguous,[10][11] but 22.4 h more likely[9]) | |
0.14±0.01[9] | ||
B−V=1.38±0.03[12][13] V−R=0.86±0.02[12][13] V−I=1.65±0.028[12][13] | ||
21.4[14] | ||
2.34[10] · 2.0[7] 1.8[3] · 1.6 (assumed)[1] | ||
Gonggong (
At approximately 1,230 km (760 mi) in diameter, Gonggong is similar in size to
Gonggong is red, likely due to the presence of
History
Discovery
Gonggong was discovered by American astronomers
Gonggong was formally announced in a
Name and symbol
The object is named after
Before its official naming, Gonggong was the largest known unnamed object in the Solar System.
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.[25][27] 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.[19] Following the Kepler spacecraft's large revision of Gonggong'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.[23]
In 2019, the discoverers of Gonggong hosted an online poll for the general public to choose between three possible names:
Having gained 46 percent of the 280,000 votes, on 29 May 2019, the discovery team announced Gonggong as the winning name.
As
Orbit
Gonggong orbits the Sun at an average distance of 67.5 AU (1.010×1010 km; 6.27×109 mi), and completes a full orbit in 554 years.
The period, inclination and eccentricity of Gonggong's orbit are all rather extreme compared to other large bodies in the Solar System. Among
The Minor Planet Center lists it as a scattered disc object for its eccentric and distant orbit.[4] The Deep Ecliptic Survey shows the orbit of Gonggong to be in a 3:10 resonance with Neptune; Gonggong completes three orbits around the Sun for every ten orbits completed by Neptune.[5]
As of 2021[update], Gonggong is about 89 AU (1.33×1010 km; 8.3×109 mi) from the Sun[36] and is moving away at a speed of 1.1 kilometers per second (2,500 miles per hour).[37] It is the eleventh-farthest known Solar System object from the Sun, preceding 2021 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), and 2018 AG37 (~ 132 AU).[36][38][39] Gonggong is more distant than Sedna, which is located 84.3 AU from the Sun as of 2021[update].[36] It has been farther from the Sun than Sedna since 2013, and it will surpass Eris in distance by 2045.[37][40]
Brightness
Gonggong has an absolute magnitude (H) of 2.34,[12][10] which makes it the seventh-brightest trans-Neptunian object known. It is dimmer than Orcus (H=2.31; D=917 km)[41] but brighter than Quaoar (H=2.82; D=1,110 km).[42] The Minor Planet Center and the Jet Propulsion Laboratory Small-Body Database assume a brighter absolute magnitude of 1.6 and 1.8, respectively,[1][3] which would make it the fifth brightest trans-Neptunian object.[43]
Being 88 AU from the Sun, the apparent magnitude of Gonggong is only 21.5,[44] and so it is too dim to be seen from Earth with the naked eye.[28][c] 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.[46][47]
Physical characteristics
Surface and spectra
The surface of Gonggong has an
Gonggong is among the reddest trans-Neptunian objects known, especially in the visible and near-infrared.
Gonggong is large enough to be able to retain trace amounts of volatile methane on its surface,[49] even when at its closest distance to the Sun (33.7 AU),[3] where temperatures are higher than that of Quaoar.[49] In particular, the large size of Gonggong means that it is likely to retain trace amounts of other volatiles, including ammonia, carbon monoxide, and possibly nitrogen, which almost all trans-Neptunian objects lose over the course of their existence.[48][10][23] Like Quaoar, Gonggong is expected to be near the mass limit at which it is able to retain those volatile materials on its surface.[48][19]
In 2022, low resolution near-infrared (0.7–5 μm) spectroscopic observations by the James Webb Space Telescope (JWST) revealed the presence of significant amounts of ethane ice (C2H6) on the surface of Gonggong, though there appears to be less ethane on Gonggong than on Sedna. The JWST spectra also contain evidence of presence of small amounts of carbon dioxide (CO2) complexed with either dark surface material or some ices as well as complex organics. On the other hand no evidence of presence of methane (CH4) and methanol (CH3OH) was found at variance with the earlier observations.[53]
Atmosphere
The presence of tholins on the surface of Gonggong implies the possible existence of a tenuous methane atmosphere, analogous to Quaoar.[51][19] Although Gonggong occasionally comes closer to the Sun than Quaoar, where it becomes warm enough that a methane atmosphere should evaporate, its larger mass could make the retention of methane just possible.[49] During aphelion, methane along with other volatiles would condense on Gonggong's surface, allowing for long-term irradiation that would otherwise result in a decrease in surface albedo.[54] The lower surface albedo would contribute to the loss of highly volatile materials such as nitrogen, as a lower albedo corresponds to more light being absorbed 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.[54]
Gonggong is thought to have had cryovolcanic activity along with a more substantial atmosphere shortly after its formation.[51][19] Such cryovolcanic activity is expected to have been brief, and the resulting atmosphere gradually escaped over time.[51][19] 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.[51][54]
Size
Year | Diameter | Method | Refs |
---|---|---|---|
2010 | 1,752 km | thermal | [55] |
2011 | 1,200+300 −200 km |
best fit albedo | [49] |
2012 | 1,280±210 km | thermal | [46] |
2013 | 1,142+647 −467 km |
thermal | [56] |
2013 | 1,290 km | radiometric | [7] |
2016 | 1,535+75 −225 km |
thermal | [10] |
2018 | 1,230±50 km | radiometric | [9] |
As of 2019, Gonggong is estimated to have a diameter of 1,230 km (760 mi), derived from radiometric measurements, its calculated mass, and assuming a density similar to other similar bodies.[9] This would make Gonggong the fifth-largest trans-Neptunian object, after Pluto, Eris, Haumea and Makemake. Gonggong is approximately the size of Pluto's moon Charon, although Gonggong's current size estimate has an uncertainty of 50 km (31 mi).[9]
The International Astronomical Union (IAU) has not addressed the possibility of officially accepting additional dwarf planets since the acceptance of Makemake and Haumea in 2008, prior to the announcement of Gonggong in 2009.[57][58] Despite not satisfying the IAU's criterion of having an absolute magnitude brighter than +1,[57][d] Gonggong is large enough to be considered a dwarf planet by several astronomers.[55][59][7] 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).[7] Scott Sheppard and colleagues think that it is likely to be a dwarf planet,[59] based on its minimum possible diameter—580 km (360 mi) under the assumption of a completely reflective surface with an albedo of 1[e]—and what was at the time the expected lower size limit of around 200 km (120 mi) for hydrostatic equilibrium in cold icy-rocky bodies.[59] However, Iapetus is not in equilibrium despite being 1,470 km (910 mi) in diameter, so this remains just a possibility.[61]
In 2010, astronomer Gonzalo 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.[55] 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.[49] A survey led by a team of astronomers using the European Space Agency's Herschel Space Observatory in 2012 determined its diameter to be 1280±210 km (795±130 mi), based on the thermal properties of Gonggong observed in the far infrared range.[46] This measurement is consistent with Brown's estimate. Later observations in 2013 using combined thermal emission data from Herschel and the Spitzer Space Telescope suggested a smaller size of 1142+647
−467 km (710+402
−290 mi), though this estimate had a larger range of uncertainty.[56]
In 2016, combined observations from the
Mass, density and rotation
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 of 1.72±0.16 g/cm3.[9] Given the mass, the 2016 size estimate of 1,535 km (954 mi) would have implied an unexpectedly low (and likely erroneous) density of 0.92 g/cm3.[9]
Gonggong is the fifth most massive trans-Neptunian object, after Eris, Pluto, Haumea, and Makemake.
The rotation period of Gonggong was first measured in March 2016, through observations of variations in its brightness with the Kepler space telescope.
Satellite
Following the March 2016 discovery that Gonggong was an unusually slow rotator, the possibility was raised that a satellite may have slowed it down via tidal forces.[63] The indications of a possible satellite orbiting Gonggong led Csaba Kiss and his team to analyze archival Hubble observations of Gonggong.[64] 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).[65] The discovery was announced in a Division for Planetary Sciences meeting on 17 October 2016.[28] The satellite is approximately 100 km (62 mi) in diameter and has an orbital period of 25 days.[64] On 5 February 2020 the satellite was officially named Xiangliu, 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]
Exploration
It was calculated by planetary scientist Amanda Zangari that a flyby mission to Gonggong would take a minimum of over 20 years with current rocket capabilities.[66] A flyby mission could take just under 25 years using a Jupiter gravity assist, based on a launch date of 2030 or 2031. Gonggong would be approximately 95 AU from the Sun when the spacecraft arrives.[66]
See also
- List of gravitationally rounded objects of the Solar System
- List of Solar System objects most distant from the Sun
- List of possible dwarf planets
Notes
- ^ Discovery was announced two years later on 7 January 2009.
- ^ In the convention for minor planet provisional designation, the first letter represents the half-month of the year of discovery while the second letter and numbers indicate the order of discovery within that half-month. In the case of 2007 OR10, the first letter 'O' corresponds to the second half-month of July 2007 while the last letter 'R' indicates that it is the 17th object discovered on the 11th cycle of discoveries. Each completed cycle consists of 25 letters representing discoveries, hence 17 + (10 completed cycles × 25 letters) = 267.[20]
- ^ Under good conditions, the unaided human eye can detect objects with a visual magnitude of around +7.4 or lower.[45]
- ^ A larger magnitude value corresponds to a dimmer brightness and vice versa. The numerical value of Gonggong's absolute magnitude is 2.34,[10] hence it is dimmer than the IAU's minimum absolute magnitude of 1.
- ^ The resulting minimum diameter of 580 km is derived from the equation , where is the absolute magnitude of Gonggong, and is the albedo of Gonggong, which in this case is assumed to be 1.[60]
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ignored (help) - ^ S2CID 119033012.
External links
- Precovery Images of Gonggong
- Gonggong's minor planet designation number
- Hubble images of Gonggong taken on 18 September 2010
- Hubble images of Gonggong taken in 2017
- The redemption of Snow White (Part 1) (Mike Brown blog 9 August 2011)
- Discovery Circumstances: Numbered Minor Planets (225001)-(230000) – Minor Planet Center
- Give Dwarf Planet 2007 OR10 the Real Name It Deserves Already – WIREDarticle by Emma Grey Ellis
- 225088 Gonggong at AstDyS-2, Asteroids—Dynamic Site
- 225088 Gonggong at the JPL Small-Body Database