![]() Hubble Space Telescope image of Varuna, taken in 2005 | |
Discovery [1] | |
---|---|
Discovered by | Spacewatch (Robert McMillan) |
Discovery date | 28 November 2000 |
Designations | |
(20000) Varuna | |
Pronunciation | /ˈværənə/ VARR-ə-nə [2] |
Named after | Varuna |
2000 WR106 | |
TNO · cubewano [3] Scat-Ext [4] | |
Adjectives | Varunian /vəˈruːniən/ [5] |
Symbol | ![]() |
Orbital characteristics [1] | |
Epoch 31 May 2020 (JD 2459000.5) | |
Uncertainty parameter 2 | |
Observation arc | 64.49 yr (23,555 days) |
Earliest precovery date | 24 November 1954 |
Aphelion | 45.117 AU (6.7494 Tm) |
Perihelion | 40.319 AU (6.0316 Tm) |
42.718 AU (6.3905 Tm) | |
Eccentricity | 0.05617 |
279.21 yr (101,980 d) | |
Average orbital speed | 4.53 km/s |
119.121° | |
0° 0m 12.708s / day | |
Inclination | 17.221° |
97.372° | |
262.220° | |
Neptune MOID | 12.040 AU (1.8012 Tm) [6] |
Physical characteristics | |
654+154 −102 km [7] 668+154 −86 km [8] | |
6.343572±0.000006 h [9] | |
0.127+0.04 −0.042 [8] | |
IR (moderately red) [10] B−V=0.88±0.02 [11] [12] V−R=0.62±0.01 [11] V−I=1.24±0.01 [11] | |
20.3 (opposition) [13] [14] | |
3.760±0.035, [8] 3.6 [1] | |
20000 Varuna [lower-alpha 1] (provisional designation 2000 WR106) is a large trans-Neptunian object in the Kuiper belt. It was discovered in November 2000 by American astronomer Robert McMillan during a Spacewatch survey at the Kitt Peak National Observatory. It is named after the Hindu deity Varuna, one of the oldest deities mentioned in the Vedic texts.
Varuna's light curve is compatible with the body being a Jacobi ellipsoid, suggesting that it has an elongated shape due to its rapid rotation. Varuna's surface is moderately red in color due to the presence of complex organic compounds on its surface. Water ice is also present on its surface, and is thought to have been exposed by past collisions which may have also caused Varuna's rapid rotation. Although no natural satellites have been found or directly imaged around Varuna, analysis of variations in its light curve in 2019 suggests the presence of a possible satellite orbiting closely around Varuna.
Varuna was discovered by American astronomer Robert McMillan using the Spacewatch 0.9-meter telescope during a routine survey on 28 November 2000. [15] The Spacewatch survey was conducted by McMillan at the Kitt Peak National Observatory near Tucson, Arizona. [1] At the time of discovery, Varuna was located at a moderately dense star field close to the northern galactic equator. [16] Although Varuna was not detected by McMillan's real-time computer software, he was able to identify Varuna moving slowly among the background stars by manually comparing multiple scans of the same region using the blinking technique. After McMillan's observing shift, follow-up observations of Varuna were conducted by astronomer Jeffrey Larsen in order to confirm the object. [15] [16] By the end of Larsen's observing shift, both McMillan and Larsen had made a total of 12 observations that spanned three nights. [15]
The discovery of Varuna was formally announced in a Minor Planet Electronic Circular on 1 December 2000. [17] It was given the provisional designation 2000 WR106, indicating that it was discovered during the second half of November 2000. [18] Varuna was the 2667th object observed in the latter half of November, as indicated by the last letter and numbers in its provisional designation. [19] At the time, Varuna was thought to be one of the largest and brightest minor planets in the Solar System due to its relatively high apparent magnitude of 20 for a distant object, which implied that it might be around one-fourth the size of Pluto and comparable in size to the dwarf planet Ceres. [15] [20] [16]
Subsequently, after the announcement of Varuna's discovery, precovery images of Varuna were found by German astronomers Andre Knofel and Reiner Stoss at the Palomar Observatory. [15] [19] One particular precovery image, which was taken with the Palomar Observatory's Big Schmidt telescope in 1955, showed that Varuna was located three degrees away from its extrapolated location based on the approximate circular orbit determined in December 2000. [15] The oldest known precovery image of Varuna was taken on 24 November 1954. [1] These precovery images along with additional observations from Japan, Hawaii, and Arizona helped astronomers refine its orbit and determine Varuna's proper classification. [20] [15] [19]
In January 2001, Varuna was assigned the minor planet number 20000 by the Minor Planet Center as its orbit was well determined from precovery images and subsequent observations. [21] [15] [19] The minor planet number 20000 was particularly chosen to commemorate Varuna's large size, being the largest classical Kuiper belt object known at that time and was believed to be as large as Ceres. [21] The number 20000 was also chosen to commemorate the coincidental 200th anniversary of the discovery of Ceres, which occurred in the same month as the numbering of Varuna. [21]
Varuna is named after the eponymous Hindu deity Varuna, following the International Astronomical Union naming convention for non-resonant Kuiper belt objects after creator deities. [15] The name was proposed by Indian choreographer Mrinalini Sarabhai, and was approved by the IAU in March 2001. [22] Varuna is one of the oldest Vedic deities of Hindu literature, being mentioned in the earliest hymns of the Rigveda . [22] [1] In Hindu literature, Varuna created and presided over the waters of the heaven and of the ocean. [23] Varuna is the king of gods and men and the universe, and has unlimited knowledge. [22] [24]
Planetary symbols are no longer much used in astronomy, so Varuna never received a symbol in the astronomical literature. There is no standard symbol for Varuna used by astrologers either. Denis Moskowitz, a software engineer in Massachusetts who designed the symbols for most of the dwarf planets, proposed a symbol for Varuna ( ): it derives from the Devanagari letter va व and Varuna's snake-lasso. This symbol is occasionally mentioned on astrology websites, but is not broadly used. [25] Another sometimes seen is a variant of Neptune (
with a globe and outward-facing tines), as Varuna is the Hindu equivalent of Neptune.
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Polar and ecliptic view of the orbits of Varuna (blue), Pluto (red), and Neptune (white). The orbital inclinations of Varuna and Pluto as shown in the ecliptic view are similar. The image on the right shows the orbits of several other large Kuiper belt objects including Pluto. |
Varuna orbits the Sun at an average distance of 42.7 AU (6.39 billion km; 3.97 billion mi), taking 279 years to complete a full orbit. [6] Its orbit is nearly circular, with a low orbital eccentricity of 0.056. Due to its low orbital eccentricity, its distance from the Sun varies slightly over the course of its orbit. Varuna's minimum distance possible (MOID) from Neptune is 12.04 AU. [6] Over the course of its orbit, Varuna's distance from the Sun ranges from 40.3 AU at perihelion (closest distance) to 45.1 AU at aphelion (farthest distance). [1] Varuna's orbit is inclined to the ecliptic by 17 degrees, similar to Pluto's orbital inclination. [1] Varuna had passed its perihelion in 1928 and is currently moving away from the Sun, approaching aphelion by 2071. [1] [13]
With a nearly circular orbit at around 40 to 50 AU, Varuna is classified as a classical Kuiper belt object (KBO). [3] Varuna's semi-major axis of 42.8 AU is similar to that of other large classical KBOs such as Quaoar (a=43.7 AU) [26] and Makemake (a=45.6 AU), [27] although other orbital characteristics such as inclination widely differ. [1] Varuna is a member of the "dynamically hot" class of classical KBOs, [10] meaning that it has an orbital inclination greater than 4 degrees, the imposed maximum inclination for dynamically cold members of its population. [28] As a classical KBO, Varuna is not in orbital resonance with Neptune and is also free from any significant perturbation by Neptune. [6] [4]
Varuna has a rapid rotation period of approximately 6.34 hours, derived from a double-peaked solution for Varuna's rotational light curve. [29] Varuna's rotation was first measured January 2001 by astronomer Tony Farnham using the McDonald Observatory's 2.1-meter telescope, as part of a study on the rotation and colors of distant objects. CCD photometry of Varuna's light curve in 2001 revealed that it displays large brightness variations with an amplitude of about 0.5 magnitudes. [30] The measured rotational light curve of Varuna provided two ambiguous rotation periods of 3.17 and 6.34 hours, for a single-peaked and a double-peaked solution, respectively. Additional possible rotation periods of 2.79 and 3.66 hours were also obtained by Farnham, although these values could not be ruled out at the time. [30] [29]
A single-peaked interpretation of Varuna's rotational light curve (3.17 h) would assume a spherical shape for Varuna, with albedo features on its surface that would account for its brightness variations. However, in order for this interpretation to be valid, Varuna must have a density much greater than 1 g/cm3 (roughly the density of water), otherwise it would deform and break apart as the given rotation period exceeds the critical rotation rate of ~3.3 hours for a body with a density of 1 g/cm3. [30] A double-peaked interpretation of Varuna's rotational light curve (6.34 h) would assume that Varuna's shape is an elongated ellipsoid, with an estimated a/b aspect ratio of 1.5–1.6. [30] [29] The rotational light curve of Varuna was later investigated by astronomers David Jewitt and Scott Sheppard during February and April 2001, and concluded that the double-peaked interpretation for Varuna's light curve is the most plausible solution due to the absence of rotational variation in Varuna's color in the visible spectrum. [31] [20]
Examination of past photometric observations of Varuna's light curve has shown that its light curve amplitude had increased by roughly 0.13 magnitudes from 2001 to 2019. [9] This increase in amplitude is due to the combined effects of Varuna's ellipsoidal shape, rotation, and varying phase angle. Geometric models for Varuna's changing amplitude have provided several possible solutions for the orientation of Varuna's rotational poles in ecliptic coordinates, with the best-fit solution adopting a spin axis right ascension and declination of 54° and −65°, respectively. [9] [lower-alpha 2] The best-fit pole orientation of Varuna implies that it is being viewed at a near-edge on configuration, in which Varuna's equator nearly faces directly toward Earth. [9] [lower-alpha 3]
Varuna's rapid rotation is believed to have resulted from disruptive collisions that have sped up its rotation during the formation of the Solar System. The present collision rate in the trans-Neptunian region is minimal, though collisions were more frequent during the formation of the Solar System. [20] However, Jewitt and Sheppard calculated that the rate of disruptive collisions among large trans-Neptunian objects (TNOs) during the Solar System's formation is extremely uncommon, contradictory to the current abundance of binary and rapidly rotating TNOs that are believed to have originated from such collisions. [20] To explain the abundance of binary and rapidly rotating TNOs, the rate of collisions among TNOs had likely increased as a result of Neptune's outward migration perturbing the orbits of TNOs, thus increasing the frequency of collisions which may have led to Varuna's rapid rotation. [20]
Year | Diameter (km) | Method | Refs |
---|---|---|---|
2000 | 900+129 −145 | thermal | [33] |
2002 | 1060+180 −220 | thermal | [31] |
2002 | ~788 | best fit albedo | [34] |
2005 | 936+238 −324 | thermal | [35] |
2005 | 600±150 | thermal | [36] |
2005 | 586+129 −190 | thermal | [37] |
2007 | 502+64.0 −69.5 or 412.3~718.2 or ≤744.1 | thermal (Spitzer 1-Band) | [38] |
2007 | >621+178.1 −139.1 | thermal (Spitzer 2-Band) | [38] |
2007 | 500±100 | thermal (adopted) | [38] |
2008 | 714+178 −128 | thermal | [39] |
2010 | 1003±9 (long-axis minimum only) | occultation | [40] |
2013 | 668+154 −86 | thermal | [8] |
2013 | ~816 | best fit albedo | [10] |
2013 | ~686 | occultation | [41] |
2014 | ~670(minimum) | occultation | [41] |
2019 | 654+154 −102 | thermal | [7] |
As a result of its rapid rotation, the shape of Varuna is deformed into a triaxial ellipsoid. Given the rapid rotation, rare for objects so large, Varuna's shape is described as a Jacobi ellipsoid, with an a/b aspect ratio of around 1.5–1.6 (in which Varuna's longest semi-axis a is 1.5–1.6 times longer than its b semi-axis). [20] [29] Examination of Varuna's light curve has found that the best-fit model for Varuna's shape is a triaxial ellipsoid with the semi-axes a, b, and c in ratios in the range of b/a = 0.63–0.80, and c/a = 0.45–0.52. [42]
Due to Varuna's ellipsoidal shape, multiple observations have provided different estimates for its diameter, ranging from 500–1,000 km (310–620 mi). [43] Most diameter estimates for Varuna were determined by measuring its thermal emission, although size estimates have been constrained to smaller values as a result of higher albedos determined by space-based thermal measurements. [43] Observations of stellar occultations by Varuna have also provided varying size estimates. [41] An occultation by Varuna in February 2010 yielded a chord length of 1,003 km (623 mi), inferred to be across its longest axis. [40] Later occultations in 2013 [44] and 2014 yielded mean diameters of 686 km (426 mi) and 670 km (420 mi) respectively. [41]
Since the discovery of Varuna, Haumea, another larger rapidly rotating (3.9 h) object over twice the size of Varuna, [lower-alpha 4] has been discovered and is also thought to have an elongated shape, [46] albeit slightly less pronounced (estimated ratios of b/a = 0.76~0.88, and c/a = 0.50~0.55, possibly due to a higher estimated density approximately 1.757–1.965 g/cm3). [42] [45]
Astronomer Gonzalo Tancredi considered Varuna likely to be a dwarf planet and a Jacobi ellipsoid in shape. [47] [48] Based on a best-fit Jacobi ellipsoid model for Varuna, Lacerda and Jewitt estimate that Varuna has a quite low density, of 0.992 g/cm3, just under Tancredi's minimum density criterion. Despite this, they assumed Varuna was in hydrostatic equilibrium for their calculations. [42] Astronomer William Grundy and colleagues propose that dark, low-density TNOs around the size range of approximately 400–1,000 km (250–620 mi) are likely to be uncompressed, partially porous bodies. While the larger objects in this range, such as Varuna, may have fully collapsed into solid material in their interiors, their surfaces likely remain uncompressed. That is, they would not be in hydrostatic equilibrium and not dwarf planets. [49]
Ground observations of Varuna's thermal emission from 2000 to 2005 yielded large diameter estimates ranging from 900 km (560 mi) to 1,060 km (660 mi), making it comparable to the size of Ceres. [43] Contrary to the ground-based estimates, space-based thermal observations from the Spitzer Space Telescope provided a smaller diameter range of 450–750 km (280–470 mi). [35] [38] The discrepancy between ground-based and space-based size estimates are due to the limited observable wavelengths for ground-based observations, as a result of absorption of Earth's atmosphere. [50] Distant trans-Neptunian objects such as Varuna intrinsically emit thermal radiation at longer wavelengths due to their low temperatures. [50] However, at long wavelengths, thermal radiation cannot pass through Earth's atmosphere and ground-based observations could only measure weak thermal emissions from Varuna at near-infrared and submillimeter wavelengths, hindering the accuracy of ground-based thermal measurements. [50] [31]
Space-based observations provided more accurate thermal measurements as they are able to measure thermal emissions at a broad range of wavelengths that are normally interfered by Earth's atmosphere. [35] [50] Preliminary thermal measurements with Spitzer in 2005 provided a higher albedo constraint of 0.12 to 0.3, corresponding to a smaller diameter constraint of 450–750 km (280–470 mi). [36] [37] Further Spitzer thermal measurements at multiple wavelength ranges (bands) in 2007 yielded mean diameter estimates around ~502 km and ~621 km for a single-band and two-band solution for the data, respectively. From these results, the adopted mean diameter was 500 km (310 mi). [38] Follow-up multi-band thermal observations from the Herschel Space Observatory in 2013 yielded a mean diameter of 668+154
−86 km, consistent with previous constraints on Varuna's diameter. [8]
Previous attempted observations of stellar occultations by Varuna in 2005 and 2008 were unsuccessful due to uncertainties in Varuna's proper motion along with undesirable conditions for observing. [51] [52] In 2010, an occultation by Varuna was successfully observed by a team of astronomers led by Bruno Sicardy on the night of 19 February. [40] The occultation was observed from various regions in southern Africa and north-eastern Brazil. [40] Although observations of the occultation from South Africa and Namibia had negative results, observations from Brazil, particularly at São Luís in Maranhão, successfully detected a 52.5-second occultation by Varuna of an 11.1 magnitude star. The occultation yielded a chord length of 1003±9 km, quite large compared to mean diameter estimates from thermal measurements. [40] Because the occultation occurred near Varuna's maximum brightness, the occultation was observing the maximum apparent surface area for an ellipsoidal shape; the longest axis of Varuna's shape was observed during the occultation. [40] São Luís was also located very close to the predicted centerline of Varuna's shadow path, [53] meaning the chord length was close to the longest measurable during the event, closely constraining the possible maximum equatorial diameter.
Results from the same event from Camalaú, Paraíba, approximately 450 km (280 mi) south (and on what was predicted to be the very southern extent of the shadow path), [53] showed a 28-second occultation, corresponding to an approximately 535 km (332 mi) chord, much longer than might otherwise have been expected. [54] However, Quixadá, 255 km (158 mi) south of São Luís–between it and Camalaú–paradoxically had a negative result. [40] To account for the negative Quixadá results, the apparent oblateness (flattening) of Varuna was imposed at a minimum value of approximately 0.56 (aspect ratio c/a ≤ 0.44), [41] corresponding to a minimum polar dimension of approximately 441.3 km (274.2 mi), based on the given chord length of 1003±9 km. [lower-alpha 5] The resulting lower bound on Varuna's polar dimension is approximately equal to Lacerda and Jewitt's lower bound c/a aspect ratio of 0.45, which they previously calculated in 2007. [42] A preliminary conference presentation, given before the Camalaú results were fully analyzed, concluded that the São Luís and Quixadá results together suggested a significantly elongated shape is required for Varuna. [40]
Later occultations in 2013 and 2014 yielded mean diameters of 686 km (426 mi) and 670 km (420 mi), respectively. [41] The mean diameter of 678 km (421 mi), calculated from both chords from the occultations, [lower-alpha 6] appears seemingly consistent with the Spitzer and Herschel thermal measurement of 668 km (415 mi). [43] While the apparent oblateness of Varuna could not be determined from the single chord obtained from the 2014 occultation, the 2013 occultation yielded two chords, corresponding to an apparent oblateness of approximately 0.29. [55] [41] The imposed oblateness for the 2013 chord length of 686 km as Varuna's diameter corresponds to a polar dimension of approximately 487 km (303 mi), [lower-alpha 7] somewhat consistent with the calculated 2010 minimum polar dimension of 441.3 km.
Varuna's spectrum was first analyzed in early 2001 with the Near Infrared Camera Spectrometer (NICS) at the Galileo National Telescope in Spain. Spectral observations of Varuna at near-infrared wavelengths revealed that the surface of Varuna is moderately red and displays a red spectral slope between the wavelength range of 0.9 and 1.8 μm. Varuna's spectrum also exhibits strong absorption bands at wavelengths of 1.5 and 2 μm, indicating the presence of water ice on its surface. [56] [31]
The red color of Varuna's surface results from the photolysis of organic compounds being irradiated by sunlight and cosmic rays. The irradiation of organic compounds such as methane on Varuna's surface produces tholins, which are known to reduce its surface reflectivity (albedo) and are expected to cause its spectrum to appear featureless. Compared to Huya, which was observed along with Varuna in 2001, it appears less red and displays more apparent water ice absorption bands, suggesting that Varuna's surface is relatively fresh and had maintained some of its original material in its surface. The fresh appearance of Varuna's surface may have resulted from collisions that have exposed fresh water ice beneath Varuna's layer of tholins above its surface. [56]
Another study of Varuna's spectra at near-infrared wavelengths in 2008 yielded a featureless spectrum with a blue spectral slope, contrary to earlier results in 2001. [57] [58] The spectra obtained in 2008 showed no clear indication of water ice, contradictory to the 2001 results. The discrepancy between the two results was interpreted as an indication of surface variation on Varuna, though this possibility was later ruled out by a 2014 study of Varuna's spectra. The 2014 results closely matched the previous spectra obtained in 2001, implying that the featureless spectra obtained in 2008 is likely erroneous. [58]
Models for Varuna's spectrum suggest that its surface is most likely formed of a mixture of amorphous silicates (25%), complex organic compounds (35%), amorphous carbon (15%) and water ice (25%), with a possibility of up to 10% methane ice. For an object with a size similar to Varuna, the presence of volatile methane could not be primordial as Varuna is not massive enough to retain volatiles on its surface. An event that had occurred subsequently after Varuna's formation–such as an energetic impact–would likely account for the presence of methane on Varuna's surface. [58] Additional near-infrared observations of Varuna's spectra were conducted at the NASA Infrared Telescope Facility in 2017 and have identified absorption features between 2.2 and 2.5 μm that might be associated with ethane and ethylene, based on preliminary analysis. [59] For mid-sized bodies such as Varuna, volatiles such as ethane and ethylene are more likely to be retained than lighter volatiles such as methane according to volatile retention theories formulated by astronomers Schaller and Brown in 2007. [59] [60]
Varuna's apparent magnitude, its brightness as seen from Earth, varies from 19.5 to 20 magnitudes. [20] At opposition, its apparent magnitude can reach up 20.3 magnitudes. [13] [14] Combined thermal measurements from the Spitzer Space Telescope and the Herschel Space Observatory in 2013 obtained a visual absolute magnitude (HV) of 3.76, comparable to that of the similarly-sized Kuiper belt object Ixion ( HV =3.83). [8] Varuna is among the twenty brightest trans-Neptunian objects known, despite the Minor Planet Center assuming an absolute magnitude of 3.6. [61] [6]
The surface of Varuna is dark, with a measured geometric albedo of 0.127 based on thermal observations in 2013. [8] Varuna's geometric albedo is similar to that of the possible dwarf planet Quaoar, which has a geometric albedo of 0.109. [62] [8] Varuna was initially thought to have a much lower geometric albedo, as early ground observations of Varuna's thermal emissions from 2000 to 2005 estimated albedo values ranging from 0.04 to 0.07, [43] around eight times darker than Pluto's albedo. [63] Later thermal measurements of Varuna with space-based telescopes refuted these previous albedo measurements: Spitzer measured a higher geometric albedo of 0.116 [38] while further thermal measurements from Spitzer and Herschel in 2013 estimated a geometric albedo of 0.127. [8]
Photometric observations of Varuna in 2004 and 2005 were carried out to observe changes in Varuna's light curve caused by opposition surges when the phase angle of Varuna approaches zero degrees at opposition. The photometry results showed that Varuna's light curve amplitude had decreased to 0.2 magnitudes at opposition, less than its overall amplitude of 0.42 magnitudes. The photometry results also showed an increase in asymmetry of Varuna's light curve near opposition, indicating variations of scattering properties over its surface. The opposition surge of Varuna differs from those of dark asteroids, which gradually becomes more pronounced near opposition in contrast to Varuna's narrow opposition surge, in which its light curve amplitude sharply changes within a phase angle of 0.5 degrees. The opposition surges of other Solar System bodies with moderate albedos behave similarly to Varuna, indirectly suggesting that Varuna might have a higher albedo in contrast to ground-based albedo estimates. [64] This implication of a higher albedo for Varuna was confirmed in subsequent thermal measurements from Spitzer and Herschel. [8]
Varuna is estimated to have a bulk density of 0.992 g/cm3, marginally less than that of water (1 g/cm3). [42] Varuna's low bulk density is likely due to a porous internal structure composed of a nearly proportional ratio of water ice and rock. [20] To explain its porous internal structure and composition, Lacerda and Jewitt suggested that Varuna may have a granular internal structure. Varuna's granular internal structure is thought to have resulted from fractures caused by past collisions likely responsible for its rapid rotation. [20] Other objects including Saturn's moons Tethys and Iapetus are also known to have a similarly low density, with a porous internal structure and a composition that is predominantly water ice and rock. [20] William Grundy and colleagues proposed that dark, low-density TNOs around the size range of approximately 400–1,000 km (250–620 mi) are transitional between smaller, porous (and thus low-density) bodies and larger, denser, brighter and geologically differentiated planetary bodies (such as dwarf planets). [49] The internal structures of low-density TNOs, such as Varuna, had only partially differentiated, as their likely rocky interiors had not reached sufficient temperatures to melt and collapse into pore spaces since formation. As a result, most mid-sized TNOs had remained internally porous, thus resulting in low densities. [49] In this case, Varuna may not be in hydrostatic equilibrium. [49]
Photometric observations of Varuna's light curve, led by Valenzuela and colleagues in 2019, indicate that a possible satellite might be orbiting Varuna at a close distance. [9] By using the Fourier analysis method of combining four separate light curves obtained in 2019, they derived a lower quality light curve amplitude with a greater amount of residuals. Their result indicated that Varuna's light curve experiences subtle changes over time. They plotted the residuals of the combined light curve in a Lomb periodogram and derived an orbital period of 11.9819 hours for the possible satellite. [9] The satellite varies in brightness by 0.04 magnitudes as it orbits Varuna. Under the assumption that Varuna's density is 1.1 g/cm3 and the satellite is tidally locked, the team estimates that it orbits Varuna at a distance of 1,300–2,000 km (810–1,240 mi), just beyond the estimated Roche limit of Varuna (~1000 km). [9] Due to the satellite's close proximity to Varuna, it is not yet possible to resolve it with space-based telescopes such as the Hubble Space Telescope as the angular distance between Varuna and the satellite is smaller than the resolution of current space-based telescopes. [9] Although direct observations of Varuna's satellite are unfeasible with current telescopes, Varuna's equator is being directly viewed at an edge-on configuration, implying that mutual events between the satellite and Varuna could possibly occur in the future. [9]
Planetary scientist Amanda Zangari calculated that a flyby mission to Varuna could take just over 12 years using a Jupiter gravity assist, based on a launch date of 2035 or 2038. Alternative trajectories using gravity assists from Jupiter, Saturn, or Uranus have been also considered. [65] A trajectory using gravity assists from Jupiter and Uranus could take just over 13 years, based a launch date of 2034 or 2037, whereas a trajectory using gravity assists from Saturn and Uranus could take under 18 years, based on an earlier launch date of 2025 or 2029. Varuna would be approximately 45 AU from the Sun when the spacecraft arrives before 2050, regardless of the trajectories used. [65]
A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has an orbital semi-major axis of 30.1 astronomical units (au).
28978 Ixion (, provisional designation 2001 KX76) is a large trans-Neptunian object and a possible dwarf planet. It is located in the Kuiper belt, a region of icy objects orbiting beyond Neptune in the outer Solar System. Ixion is classified as a plutino, a dynamical class of objects in a 2:3 orbital resonance with Neptune. It was discovered in May 2001 by astronomers of the Deep Ecliptic Survey at the Cerro Tololo Inter-American Observatory, and was announced in July 2001. The object is named after the Greek mythological figure Ixion, who was a king of the Lapiths.
Haumea is a dwarf planet located beyond Neptune's orbit. It was discovered in 2004 by a team headed by Mike Brown of Caltech at the Palomar Observatory, and formally announced in 2005 by a team headed by José Luis Ortiz Moreno at the Sierra Nevada Observatory in Spain, who had discovered it that year in precovery images taken by the team in 2003. From that announcement, it received the provisional designation 2003 EL61. On 17 September 2008, it was named after Haumea, the Hawaiian goddess of childbirth, under the expectation by the International Astronomical Union (IAU) that it would prove to be a dwarf planet. Nominal estimates make it the third-largest known trans-Neptunian object, after Eris and Pluto, and approximately the size of Uranus's moon Titania. Precovery images of Haumea have been identified back to 22 March 1955.
Makemake is a dwarf planet and the second-largest of what is known as the classical population of Kuiper belt objects, with a diameter approximately that of Saturn's moon Iapetus, or 60% that of Pluto. It has one known satellite. Its extremely low average temperature, about 40 K (−230 °C), means its surface is covered with methane, ethane, and possibly nitrogen ices. Makemake shows signs of geothermal activity and thus may be capable of supporting active geology and harboring an active subsurface ocean.
(19308) 1996 TO66 (provisional designation 1996 TO66) is a trans-Neptunian object that was discovered in 1996 by Chadwick Trujillo, David Jewitt and Jane Luu. Until 20000 Varuna was discovered, it was the second-largest known object in the Kuiper belt, after Pluto.
38628 Huya ( hoo-YAH; provisional designation 2000 EB173) is a binary trans-Neptunian object located in the Kuiper belt, a region of icy objects orbiting beyond Neptune in the outer Solar System. Huya is classified as a plutino, a dynamical class of trans-Neptunian objects with orbits in a 3:2 orbital resonance with Neptune. It was discovered by the Quasar Equatorial Survey Team and was identified by Venezuelan astronomer Ignacio Ferrín in March 2000. It is named after Juyá, the mythological rain god of the Wayuu people native to South America.
(55565) 2002 AW197 (provisional designation 2002 AW197) is a classical, non-resonant trans-Neptunian object from the Kuiper belt in the outermost region of the Solar System, also known as a cubewano. With a likely diameter of at least 600 kilometers (400 miles), it is approximately tied with 2002 MS4 and 2013 FY27 (to within measurement uncertainties) as the largest unnamed object in the Solar System. It was discovered at Palomar Observatory in 2002.
(55637) 2002 UX25 (provisional designation 2002 UX25) is a trans-Neptunian object that orbits the Sun in the Kuiper belt beyond Neptune. It briefly garnered scientific attention when it was found to have an unexpectedly low density of about 0.82 g/cm3. It was discovered on 30 October 2002, by the Spacewatch program; as of June 2024, the object has yet to be named.
(55636) 2002 TX300 is a bright Kuiper belt object in the outer Solar System estimated to be about 286 kilometres (178 mi) in diameter. It is a large member of the Haumea family that was discovered on 15 October 2002 by the Near-Earth Asteroid Tracking (NEAT) program.
(307261) 2002 MS4 (provisional designation 2002 MS4) is a large trans-Neptunian object in the Kuiper belt, which is a region of icy planetesimals beyond Neptune. It was discovered on 18 June 2002 by Chad Trujillo and Michael Brown during their search for bright, Pluto-sized Kuiper belt objects at Palomar Observatory. To within measurement uncertainties, 2002 MS4, 2002 AW197, and 2013 FY27 have a diameter close to 800 km (500 mi), which makes them the largest unnamed objects in the Solar System. 2002 MS4 is large enough that astronomers consider it a possible dwarf planet.
(208996) 2003 AZ84 (provisional designation 2003 AZ84) is a trans-Neptunian object with a possible moon located in the outer regions of the Solar System. It is approximately 940 kilometers across its longest axis, as it has an elongated shape. It belongs to the plutinos – a group of minor planets named after its largest member Pluto – as it orbits in a 2:3 resonance with Neptune in the Kuiper belt. It is the third-largest known plutino, after Pluto and Orcus. It was discovered on 13 January 2003, by American astronomers Chad Trujillo and Michael Brown during the NEAT survey using the Samuel Oschin telescope at Palomar Observatory.
174567 Varda (provisional designation 2003 MW12) is a binary trans-Neptunian planetoid of the resonant hot classical population of the Kuiper belt, located in the outermost region of the Solar System. Its moon, Ilmarë, was discovered in 2009.
(84922) 2003 VS2 is a trans-Neptunian object discovered by the Near Earth Asteroid Tracking program on 14 November 2003. Like Pluto, it is in a 2:3 orbital resonance with Neptune and is thus a plutino. Analysis of light-curve suggests that it is not a dwarf planet.
Salacia is a large trans-Neptunian object in the Kuiper belt, approximately 850 km (530 mi) in diameter. It was discovered on 22 September 2004, by American astronomers Henry Roe, Michael Brown and Kristina Barkume at the Palomar Observatory in California, United States. Salacia orbits the Sun at an average distance that is slightly greater than that of Pluto. It was named after the Roman goddess Salacia and has a single known moon, Actaea.
Gonggong is a dwarf planet and a member of the scattered disc beyond Neptune. It has a highly eccentric and inclined orbit during which it ranges from 34–101 astronomical units from the Sun. As of 2019, its distance from the Sun is 88 AU, and it is the sixth-farthest known Solar System object. According to the Deep Ecliptic Survey, Gonggong is in a 3:10 orbital 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 astronomers Megan Schwamb, Michael Brown, and David Rabinowitz at the Palomar Observatory, and the discovery was announced in January 2009.
Quaoar is a large, ringed dwarf planet in the Kuiper belt, a region of icy planetesimals beyond Neptune. It has an elongated ellipsoidal shape with an average diameter of 1,090 km (680 mi), about half the size of the dwarf planet Pluto. The object was discovered by American astronomers Chad Trujillo and Michael Brown at the Palomar Observatory on 4 June 2002. Quaoar's surface contains crystalline water ice and ammonia hydrate, which suggests that it might have experienced cryovolcanism. A small amount of methane is present on its surface, which can only be retained by the largest Kuiper belt objects.
Vanth is a natural satellite or moon of the large trans-Neptunian dwarf planet Orcus. It was discovered by Michael Brown and Terry-Ann Suer using images taken by the Hubble Space Telescope on 13 November 2005. The moon has a diameter of 443 km (275 mi), making it about half the size of Orcus and the third-largest moon of a trans-Neptunian object. Vanth is massive enough that it shifts the barycenter of the Orcus–Vanth system outside of Orcus, forming a binary system in which the two bodies revolve around the barycenter, much like the Pluto–Charon system. It is hypothesized that both systems formed similarly, most likely by a giant impact early in the Solar System's history. In contrast to Orcus, Vanth has a darker and slightly redder surface that apparently lacks exposed water ice, resembling primordial Kuiper belt objects.
Weywot is a natural satellite or moon of the trans-Neptunian dwarf planet Quaoar. It was discovered by Michael Brown and Terry-Ann Suer using images taken by the Hubble Space Telescope on 14 February 2006. Named after the Tongva sky god and son of Quaoar, Weywot is thought to be a fragment of Quaoar that was ejected into an eccentric orbit around the dwarf planet by a major impact event billions of years ago. The moon is nearly 200 km (120 mi) in diameter and it orbits Quaoar every 12.4 days at an average distance of 13,300 km (8,300 mi). Weywot is thought to play a role in maintaining Quaoar's outer ring by gravitationally influencing it in an orbital resonance.
(55638) 2002 VE95 (provisional designation 2002 VE95) is a trans-Neptunian object from the outermost region of the Solar System. It was discovered on 14 November 2002, by astronomers with the Near-Earth Asteroid Tracking program at the Palomar Observatory in California, United States. This resonant trans-Neptunian object is a member of the plutino population, locked in a 2:3 resonance with Neptune. The object is likely of primordial origin with a heterogeneous surface and a notably reddish color (RR) attributed to the presence of methanol and tholins. It has a poorly defined rotation period of 6.8 hours and measures approximately 250 kilometers (160 miles) in diameter, too small to be a dwarf planet candidate. As of 2021, it has not yet been named.
(275809) 2001 QY297 is a trans-Neptunian object from the classical Kuiper belt, located in the outermost region of the Solar System. The binary classical Kuiper belt object belongs to the cold population.
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