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2018 VG18
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2018 VG18
Discovery images of 2018 VG18
Discovery[1][2]
Discovered byS. S. Sheppard
D. Tholen
C. Trujillo
Discovery siteMauna Kea Obs.
Discovery date10 November 2018
Designations
2018 VG18
"Farout" (nickname)[3]
TNO[4] · SDO[5]
resonant (2:9)[6] · distant[2]
Orbital characteristics (barycentric)[7][4]
Epoch 25 February 2023 (JD 2460000.5)
Uncertainty parameter 6
Observation arc16.15 yr (5,900 d)
Earliest precovery date21 November 2003[2]
Aphelion124.897±0.043 AU
(occurs 2063)[8]
Perihelion38.358±0.030 AU
81.628±0.028 AU
Eccentricity0.5301±0.0004
737.01±0.38 yr
157.653°±0.473°
0° 0m 4.814s / day
Inclination24.292°±0.002°
245.325°±0.001°
≈ 1696[9]
±30 years
16.865°±0.171°
Known satellites0
Physical characteristics
490 to 790 km (assuming an albedo 0.12)[10][11]
500 km (est.)[3]
24.6[12]
3.94±0.52[4]

2018 VG18 is a distant trans-Neptunian object (TNO) that was discovered when it was 123 AU (18 billion km; 11 billion mi) from the Sun, more than three times the average distance between the Sun and Pluto. It was discovered on 10 November 2018 by Scott Sheppard, David Tholen, and Chad Trujillo during their search for TNOs whose orbits might be gravitationally influenced by the hypothetical Planet Nine. They announced the discovery of 2018 VG18 on 17 December 2018 and nicknamed the object "Farout" to emphasize its distance from the Sun.

2018 VG18 is the second-most distant natural object ever observed in the Solar System, after 2018 AG37 (132 AU), which was also discovered by Sheppard's team in January 2018. As of 2024, 2018 VG18 is 123.6 AU (18 billion km) from the Sun and is moving farther away until it reaches aphelion in 2063.[8] While 2018 VG18 is one of the most distant Solar System objects known, its orbit is not the most distant since its average orbital distance from the Sun is 82 AU, which places it in the scattered disk and the 2:9 orbital resonance with Neptune.

2018 VG18 has not yet been imaged by high-resolution telescopes, so it has no known moons.[13] The Hubble Space Telescope is planned to image 2018 VG18 in 2026, which should determine if it has significantly sized moons.[13] Its size has not been measured, but should be in the range of 490 to 790 km in diameter if it has a moderate albedo.[10]

Discovery

[edit]
Animation of two discovery images taken by the 8.2-meter Subaru Telescope on 10 November 2018. The moving dot in the center is 2018 VG18 at magnitude 24.6.

2018 VG18 was discovered by astronomers Scott Sheppard, David Tholen, and Chad Trujillo at the Mauna Kea Observatory in Hawaii on 10 November 2018.[1][3] The discovery formed part of their search for distant trans-Neptunian objects (TNOs) with orbits that may be gravitationally perturbed by the hypothesized Planet Nine. The search team had been involved in the discoveries of several other distant TNOs, including the sednoids 2012 VP113 and 541132 Leleākūhonua.[3][14] 2018 VG18 was first identified as a faint object slowly moving in two images taken with the 8.2-meter Subaru Telescope on the night of 10 November 2018.[1][3] At the time of discovery, 2018 VG18 was located in the constellation Taurus,[a] at a faint apparent magnitude of 24.6, approaching the lowest detectable magnitude limit for most telescopes.[1][15]

2018 VG18's low on-sky motion and brightness indicated that it is very distant, which prompted additional follow-up observations to constrain measurements of its orbit and distance.[3] The object was reobserved in December 2018 by Sheppard at the Las Campanas Observatory, with observation times spanning ten days.[1] However, its orbit remained with a significant uncertainty due to its short observation arc. Nonetheless, the discovery of 2018 VG18 along with a preliminary orbit solution was formally announced in a Minor Planet Electronic Circular issued by the Minor Planet Center on 17 December 2018.[1]

Since the discovery announcement, 2018 VG18 has been periodically observed by Sheppard at the Las Campanas and Mauna Kea observatories.[16] Additional observations were also made at the Roque de los Muchachos Observatory in November 2019 and January 2020.[17] As of 2022, 2018 VG18 has been observed for over five oppositions, with an observation arc of 16 years (5,900 days). Several precovery observations of 2018 VG18 have been identified in images taken by the Cerro Tololo Observatory's Dark Energy Camera on 11 March 2015 and 16 January 2017, as well as images taken by the Canada-France-Hawaii Telescope and Subaru Telescope in November 2003 and September 2005, respectively.[2]

Nomenclature

[edit]

The discoverers gave 2018 VG18 the nickname "Farout" for its distant location from the Sun, and particularly because it was the farthest known TNO observed at the time.[3] On the same day, the object was formally given the provisional designation 2018 VG18 by the Minor Planet Center.[1] The provisional designation indicates the object's discovery date, with the first letter representing the first half of November and the succeeding letter and numbers indicating that it is the 457th object discovered during that half-month.[b] The object has not yet been assigned an official minor planet number by the Minor Planet Center due to its short observation arc and orbital uncertainty.[2] 2018 VG18 is expected to receive a minor planet number once it has been observed for at least four oppositions, which would take several years.[18][3] Once it receives a minor planet number, the object will be eligible for naming by its discoverers.[18]

Orbit and classification

[edit]
See also: List of Solar System objects most distant from the Sun

2018 VG18's average orbital distance from the Sun is approximately 82 AU and it takes approximately 737 years to complete one orbit.[7][c] Simulations of 2018 VG18's orbit by Marc Buie show that 2018 VG18 is in a 2:9 orbital resonance with Neptune—2018 VG18 orbits exactly twice for every nine orbits completed by Neptune.[6] With an orbital eccentricity of about 0.53, it follows a highly elongated orbit, varying in distance from 38 AU at perihelion to 125 AU at aphelion. Its orbit is inclined to the ecliptic plane by about 24 degrees, with its aphelion oriented below the ecliptic. At perihelion, 2018 VG18 approaches close to Neptune's orbit without crossing it, having a minimum orbit intersection distance of approximately 8 AU.[2] Because 2018 VG18 approaches Neptune at close proximity, its orbit has likely been perturbed and scattered by Neptune; thus, it falls into the category of scattered-disc objects.[5][14] 2018 VG18 last passed its perihelion in the late 17th century.[4]

As of 2024, 2018 VG18 is the second-most distant observed Solar System object from the Sun and is the first object discovered while beyond 100 astronomical units (AU), overtaking the dwarf planet Eris (96 AU) in observed distance.[17][3] 2018 VG18's distance from the Sun is 123.6 AU (18.5 billion km; 11.5 billion mi) as of 2024,[12] more than three times the average distance between the Sun and Pluto (39.5 AU).[15] For comparison, the Voyager 2 and Voyager 1 space probes were approximately 120 AU and 144 AU from the Sun at the time of 2018 VG18's discovery, respectively.[14] At its current distance, 2018 VG18 is thought to be close to the heliopause, the boundary where the Sun's solar wind is stopped by the interstellar medium at around 120 AU.[14] The new orbit determination indicates that this object is currently very close to aphelion which it should reach in mid-2063,[8] and that it is a member of the scattered disc.

While 2018 VG18 is one of the most distant objects observed, it does not have the largest orbital semi-major axis.[5] For comparison, the semi-major axis of the planetoid 90377 Sedna is about 500 AU.[20] In an extreme case, the scattered-disc object 2014 FE72 has a semi-major axis around 1,400 AU,[21] though its distance from the Sun as of 2021 is about 64 AU, approximately half 2018 VG18's distance from the Sun in that year.[22]

At the time of discovery on 10 November 2018, 2018 VG18's distance from the Sun was 123.4 AU, and has since moved to 123.6 AU from the Sun as of 2024.[12] As it is approaching aphelion, 2018 VG18 is receding from the Sun at a rate of 0.06 AU per year, or 0.3 km/s (670 mph).[12] 2018 VG18 was the farthest TNO known until February 2019, when 2018 AG37 (nicknamed "FarFarOut") was discovered at about 132 AU by Sheppard's team.[17] While 2018 VG18 and 2018 AG37 are among the farthest Solar System objects observable,[17] some historical near-parabolic comets are much further from the Sun. For example, Caesar's Comet (C/-43 K1) is over 800 AU from the Sun while Comet Donati (C/1858 L1) is over 145 AU from the Sun as of 2021.[23][24]

The orbit of 2018 VG18[4]
Ecliptic polar view of 2018 VG18's orbit (top)
Oblique view of 2018 VG18's orbit
2018 VG18's retrograde motion in the sky through the constellation Taurus
Orbit diagram of several extreme trans-Neptunian objects, with scattered-disc objects Eris and 2018 VG18 included

Physical characteristics

[edit]

The size of 2018 VG18 is unmeasured, but based on its intrinsic brightness, it is likely large enough to make it a dwarf planet candidate.[3] Based on its apparent brightness and large distance, 2018 VG18's absolute magnitude is estimated to be in the range of 3.4–4.5.[4] According to the Minor Planet Center, it is the ninth intrinsically brightest scattered-disc object.[5]

The albedo (reflectivity) of 2018 VG18 has not been measured nor constrained, thus its diameter can not be calculated with certainty. Assuming that the albedo of 2018 VG18 is within the range of 0.10–0.15, its diameter should be around 440–870 km (270–540 mi).[25]

See also

[edit]

Notes

[edit]

References

[edit]
[edit]

Grokipedia

2018 VG18

View on Grokipedia
from Grokipedia
2018 VG18, nicknamed Farout, is a large trans-Neptunian object (TNO) and dwarf planet candidate located in the scattered disc region of the outer Solar System.[1] Discovered on November 10, 2018, it was the first Solar System object observed at a distance greater than 100 astronomical units (AU) from the Sun, with an initial detection placing it at approximately 120 AU.[1] Estimated to have a diameter of about 500 kilometers, it appears as a slow-moving, pinkish body indicative of an ice-rich surface composition.[1] The object was found by astronomers Scott S. Sheppard of Carnegie Institution for Science, David J. Tholen of the University of Hawaiʻi, and Chad Trujillo of Northern Arizona University using the Subaru Telescope atop Mauna Kea in Hawaii.[1] Its highly eccentric orbit has a semi-major axis of 82 AU, perihelion distance of 39 AU (well beyond Neptune's orbit), and aphelion of 125 AU, yielding an orbital period of roughly 740 years.[2] At discovery, 2018 VG18 was near its aphelion, contributing to its extreme remoteness and faint absolute magnitude of about 4.[2] Although no longer the most distant observed Solar System object, having been surpassed by 2018 AG37 (nicknamed Farfarout) at 132 AU in 2021, 2018 VG18 remains significant for advancing searches for extreme TNOs potentially influenced by a hypothetical Planet Nine.[3] The recent discovery of 2017 OF201 in 2025, with an extremely wide orbit (semi-major axis of about 838 AU), further highlights such efforts.[4] As of 2025, observations have refined its orbit to a semi-major axis of 81.6 AU, but physical properties remain based on initial estimates, underscoring its role in understanding the dynamical architecture of the Kuiper Belt's outer edges.[2]

Discovery and Nomenclature

Discovery

2018 VG18 was discovered on November 10, 2018, by astronomers Scott S. Sheppard of the Carnegie Institution for Science, David J. Tholen of the University of Hawaiʻi, and Chad A. Trujillo of Northern Arizona University, using the 8.2-meter Subaru Telescope atop Mauna Kea in Hawaiʻi.[1][5] The detection occurred during an ongoing survey aimed at identifying extreme trans-Neptunian objects (TNOs) in the outer Solar System, particularly those whose orbits might provide evidence for the hypothetical Planet Nine.[1] This search focused on faint, distant bodies that could reveal gravitational influences from unseen massive planets. The initial detection appeared as a faint, slowly moving point source in survey images captured that night, prompting immediate follow-up observations to confirm its existence and trajectory.[5] Subsequent imaging with the 6.5-meter Magellan Baade Telescope at Las Campanas Observatory in Chile verified the object's position and extreme distance, estimated at approximately 120 AU from the Sun at the time of discovery.[1][6] These observations established 2018 VG18 as the first Solar System object detected beyond 100 AU. The discovery was formally announced on December 17, 2018, through Minor Planet Electronic Circular (MPEC) 2018-Y14 issued by the Minor Planet Center, which assigned the provisional designation 2018 VG18 based on the 11 observations compiled up to December 12, 2018.[6] At announcement, preliminary orbital analysis indicated a highly eccentric path consistent with a scattered disc object.[1]

Nomenclature

2018 VG18 received its provisional designation from the Minor Planet Center (MPC) on December 17, 2018, following its initial detection, following the standard format for minor planets based on the discovery year (2018) and the sequence of observations within that half-month period (VG18).[7][1] At the time of announcement, the object's observation arc spanned only 32 days, from its first detection on November 10, 2018, using the Subaru Telescope to confirmatory observations on December 12, 2018, with the Magellan Baade Telescope; this limited arc prevented a reliable determination of its full orbit.[1] As of 2025, additional observations, including precoveries from 2003, 2005, 2015, and 2017, have extended the arc to 5,888 days with 35 total measurements, yet 2018 VG18 remains unnumbered by the MPC due to ongoing orbital uncertainties (MPC uncertainty parameter U=6), which require observations across at least four oppositions for permanent numbering under International Astronomical Union (IAU) guidelines.[7][8][9] The discovery team, led by Scott S. Sheppard of Carnegie Institution for Science, coined the informal nickname "Farout" to emphasize the object's record-breaking distance of approximately 120 AU from the Sun at the time of discovery, marking it as the farthest known Solar System body observed to date.[1] As a non-numbered minor planet, 2018 VG18 has no official IAU-approved name and awaits sufficient long-term observations to secure its orbit for numbering, after which the discoverers may propose a permanent name adhering to IAU nomenclature conventions.[7][9]

Orbital Characteristics

Orbit

2018 VG18 follows a highly elliptical orbit around the Sun, characterized by a semi-major axis of 81.628 AU, which defines its average distance from the Sun.[2] This places the object in the outer reaches of the Solar System, far beyond the orbit of Neptune at approximately 30 AU. The orbit's eccentricity of 0.53 results in significant variations in its distance from the Sun, ranging from a perihelion of 38.358 AU to an aphelion of 124.897 AU, the latter expected to be reached around 2063.[2] With an orbital inclination of 24.292° relative to the ecliptic plane, the path deviates notably from the plane in which most planets orbit, contributing to its isolated dynamical environment.[2] The orbital period of 2018 VG18 is approximately 737 years, reflecting the extended time required to complete one full revolution given its large semi-major axis, as governed by Kepler's third law.[2] As of November 2025, the object is positioned about 123.6 AU from the Sun, near its aphelion and moving slowly due to the weak gravitational influence at such distances.[10] These parameters have been refined through an observation arc spanning several years following its discovery in November 2018, incorporating data from multiple telescopes to improve the accuracy of the orbital fit despite the object's faintness and slow apparent motion.[2] This elongated, inclined trajectory classifies 2018 VG18 as a scattered disc object.[2]

Classification

2018 VG18 is a trans-Neptunian object (TNO), residing beyond the orbit of Neptune in the outer Solar System.[1] Dynamically, it is classified as a scattered disc object (SDO), a category of TNOs with highly eccentric orbits perturbed by close encounters with Neptune, leading to their detachment from the Kuiper Belt. This object maintains a 2:9 mean-motion resonance with Neptune, completing two orbits around the Sun for every nine of Neptune's, which contributes to the long-term stability of its distant path despite its scattered dynamics.[11] Based on its absolute magnitude suggesting a diameter of around 500 km, 2018 VG18 qualifies as a potential dwarf planet candidate under International Astronomical Union (IAU) criteria for hydrostatic equilibrium, but insufficient observations of its shape prevent confirmation, and it remains unrecognized as a dwarf planet by the IAU as of 2025.[12] Upon discovery, 2018 VG18 held the record as the most distant observed Solar System object at over 120 AU, but this status was eclipsed in 2021 by 2018 AG37 (Farfarout), currently at about 132 AU.[13]

Physical Characteristics

Size and Shape

The absolute magnitude of 2018 VG18 is measured at 3.94 ± 0.52, a value that underscores its intrinsic faintness, exacerbated by its extreme distance from the Sun.[2] Size estimates for 2018 VG18 are derived indirectly from its photometric brightness, as the object remains unresolved in direct imaging efforts as of 2025. Assuming a geometric albedo of 0.12—typical for trans-Neptunian objects—the diameter is estimated to range from 490 to 790 km. Lower albedo values, such as those below 0.05 observed in some icy bodies, could imply a larger size approaching 1,000 km to account for the observed luminosity. These photometric derivations place 2018 VG18 among the larger known trans-Neptunian objects, with a nominal diameter of approximately 500 km.[1][14] Given its estimated dimensions, 2018 VG18 is presumed to have achieved hydrostatic equilibrium, resulting in a largely rounded shape consistent with dwarf planet candidates. This form is expected for objects exceeding roughly 400 km in diameter, where self-gravity overcomes material rigidity to drive spheroidal configurations.[14] The mass of 2018 VG18 remains undetermined, as no natural satellites have been detected and insufficient gravitational perturbation data on nearby objects exists to infer it reliably.[1]

Color and Composition

2018 VG18 displays a pinkish hue in visible light observations, a coloration commonly observed in ice-rich trans-Neptunian objects and attributed to the long-term irradiation of surface ices by cosmic rays and ultraviolet radiation over billions of years, leading to the formation of reddish organic tholins.[1][15] The surface composition of 2018 VG18 is inferred from its pinkish color to be dominated by water ice, with potential traces of methane or other volatile ices, similar to other ice-rich extreme trans-Neptunian objects such as Sedna.[1] As of 2025, detailed spectroscopic observations remain pending to confirm surface composition. This matches the general characteristics of extreme TNOs in a low-temperature environment estimated at approximately 20 K, reflecting the object's extreme isolation from solar heating.[16][17] Given its small size and frigid surface conditions, 2018 VG18 shows no evidence of retaining an atmosphere, as volatiles would sublimate and escape in such a tenuous environment.[18] This preserved icy composition suggests that 2018 VG18 represents primordial material from the early Solar System, shielded from dynamical perturbations and external processing due to its detached orbit.[19]

Significance and Observations

Role in Solar System Studies

The discovery of 2018 VG18 occurred during an ongoing survey for extreme trans-Neptunian objects (eTNOs), aimed at identifying potential evidence for the hypothetical Planet Nine through the analysis of orbital clustering and alignments among distant TNOs.[1] As one of these eTNOs, its position and trajectory contribute valuable data to dynamical models that examine whether an undiscovered massive planet could be shepherding such objects into aligned orbits.[12] At the time of its announcement in December 2018, 2018 VG18 held the record as the most distant naturally occurring object observed in the Solar System, located at approximately 120 AU from the Sun—more than three times farther than Pluto's current distance.[1] This milestone underscored the challenges of detecting faint, slow-moving bodies at such extremes, but the record was surpassed in 2021 by 2018 AG37 (nicknamed Farfarout), which orbits at an average distance of 132 AU, and again in 2025 by 2017 OF201 with its extremely wide orbit.[20][4] The object's orbital parameters, including an eccentricity of roughly 0.53 and an inclination of about 24 degrees relative to the ecliptic, point to a history of gravitational perturbations, likely from close encounters with Neptune or other giant planets during the early Solar System's migration phase, which scattered it into the distant scattered disc. Such dynamics also align with broader hypotheses involving unseen masses, like Planet Nine, that could further influence the eccentric and inclined paths of eTNOs like 2018 VG18. As a member of the scattered disc population, 2018 VG18 helps refine our understanding of the outer Solar System's architecture among the over 5,000 known trans-Neptunian objects, particularly by probing the sparse distribution beyond the Kuiper Cliff—a sharp decline in TNO density around 50 AU that marks the transition to more dynamically excited regions.[21] Its extreme distance precludes dedicated spacecraft missions, as no current or planned probe can reach beyond 100 AU in the foreseeable future; nonetheless, findings from 2018 VG18 inform the context for extended missions like New Horizons, which continues to characterize the Kuiper Belt and scattered disc through remote observations and flybys of comparable distant targets.

Current and Future Observations

Following its discovery, 2018 VG18 underwent initial follow-up observations in late 2018 and into 2019 to extend its observational arc and refine preliminary orbital estimates. These efforts included imaging with the Magellan telescopes at Las Campanas Observatory in Chile, which confirmed the object's distance at approximately 120 AU and provided data over multiple nights in early December 2018.[1] Additional sessions at Las Campanas spanned over a week in early December 2018, capturing the object's slow motion against the background stars.[12] By 2019, these ground-based observations had accumulated enough data points to improve the arc length, though the object's faintness and remoteness limited the precision of early measurements.[14] As of 2025, the object's position is predicted at 123.6 AU using ephemeris data from NASA's JPL Horizons system, with the last observations from January 2020 contributing to a total of 34 observations spanning 2003 to 2020.[2] Ongoing monitoring is challenging due to its faintness, but the Vera C. Rubin Observatory, commencing full operations in late 2025, is expected to enhance this monitoring by providing wide-field imaging capable of detecting faint, slow-moving outer Solar System objects like 2018 VG18 for further orbit refinements.[22] Observing 2018 VG18 presents significant challenges due to its extreme distance, resulting in exceedingly slow apparent motion—requiring years of tracking to accumulate sufficient data for robust orbital models.[1] Its faint visual magnitude, around 24, further limits resolution from ground-based facilities, restricting detailed imaging to brief glimpses rather than sustained high-fidelity views.[12] Ground-based efforts, such as those with Subaru, face additional constraints from atmospheric interference and the need for long exposure times, underscoring the value of future space-based observations to overcome these limitations.[5]
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