Vanth (moon)

Last updated
Vanth
Orcus-Vanth discovery.jpg
Discovery image of Vanth by the Hubble Space Telescope in November 2005
Discovery
Discovered by Michael E. Brown
T.-A. Suer
Discovery date13 November 2005 [lower-alpha 1]
Designations
Designation
Orcus I
Pronunciation /ˈvænθ/
S/2005 (90482) 1
Adjectives Vanthian
Orbital characteristics [3]
8999.8±9.1 km
Eccentricity 0.00091±0.00053 km
9.539154±0.00002 d
Inclination 105.03±0.18°
Satellite of Orcus
Physical characteristics
Dimensions434.4±2.4  km (single occultation chord; smaller than 442.5±10.2 km if spherical) [4]
475±75  km [5]
Mass (3.6–6.8)×1019 kg [lower-alpha 2]
Mean density
0.8–1.5 g/cm3 [4]
synchronous [6]
Albedo 0.12 [7]
0.08+0.02
−0.01
[5]
Spectral type
moderately red (optical) [8]
21.97 ± 0.05 [8]
4.88 ± 0.05 [8]

    Vanth, full designation (90482) Orcus I Vanth, is the single known natural satellite of the plutino and likely dwarf planet 90482 Orcus. With a diameter of about 440 km, it is half the size of Orcus and probably the third-largest known moon of a known trans-Neptunian object, after Pluto I Charon and Eris I Dysnomia, though it is possible that the poorly resolved Varda I Ilmarë or Haumea I Hiʻiaka might be comparable in size. Vanth was discovered by Michael Brown and T.-A. Suer using discovery images taken by the Hubble Space Telescope on 13 November 2005. [1] The discovery was announced in an IAU Circular notice published on 22 February 2007. [2]

    Contents

    Using observations with the Hubble Space Telescope from 13 November 2005, Michael Brown and T. A. Suer detected a natural satellite. [1] The discovery of a satellite of Orcus was reported in an IAU Circular notice published on 22 February 2007. [2] The satellite was given the designation S/2005 (90482) 1 before later being named Vanth. It orbits Orcus in a nearly face-on circular orbit with an eccentricity of about 0.007, and an orbital period of 9.54 days. [8] Vanth orbits only 9,030 km (5,610 mi) from Orcus and is too close to Orcus for ground-based spectroscopy to determine the surface composition of the satellite. [7]

    Brown suspects that like the Pluto–Charon system, which are similar in their relative sizes, Orcus and Vanth are tidally locked. [9] Vanth does not resemble known collisional satellites because its spectrum is very different from that of its primary, and it may be a captured Kuiper belt object. [9] Vanth could also have originated as a result of rotational fission of the primordial Orcus, which would have rotated much faster than now. [6]

    Name

    Upon discovery, Vanth was issued a provisional designation, S/2005 (90482) 1. On 23 March 2009, Brown asked readers of his weekly column to suggest possible names for the satellite, with the best one to be submitted to the International Astronomical Union (IAU) on 5 April. [9] The name Vanth, the winged Etruscan psychopomp who guides the souls of the dead to the underworld, was chosen from among a large pool of submissions. Vanth was the only suggestion that was purely Etruscan in origin. It was the most popular submission, first suggested by Sonya Taaffe. [10] This submission was assessed and approved by the IAU's Committee for Small Body Nomenclature, in accordance with the naming procedures for minor planets and satellites. [11] [12] The official naming citation was announced in a Minor Planet Circular notice published on 30 March 2010. [13]

    The Etruscan Vanth is frequently portrayed in the company of Charun (Charon), and so as the name of the moon of Orcus (nicknamed the "anti-Pluto" because resonance with Neptune keeps it on the opposite side of the Sun from Pluto), it is an allusion to the parallels between Orcus and Pluto. Brown quoted Taaffe as saying that if Vanth "accompanies dead souls from the moment of death to the underworld itself, then of course her face is turned always toward Orcus", a reference to the likely synchronous orbit of Vanth about Orcus. [10]

    Characteristics

    Hubble image sequence of Vanth orbiting Orcus Orcus-Vanth orbit.gif
    Hubble image sequence of Vanth orbiting Orcus
    Model of Orcus and Vanth with its orbit nearly aligned face-on with the Sun and Earth's direction Orcus Vanth orbit.png
    Model of Orcus and Vanth with its orbit nearly aligned face-on with the Sun and Earth's direction
    Orcus and Vanth imaged by Hubble in 2006 Orcus-Vanth.gif
    Orcus and Vanth imaged by Hubble in 2006

    Vanth was found at 0.25 arcseconds from Orcus with magnitude difference of 2.7±1.0. [1] Estimates made in 2009 by Brown show that the apparent magnitude of Vanth is 21.97±0.05 which is 2.54±0.01 magnitudes fainter than Orcus. [8] Assuming equal albedos this would mean a diameter of 280 km (170 mi), or 2.9 times smaller than the primary. [7] However, the dissimilar colors of Orcus (neutral) and Vanth (red) suggest that Vanth could have an albedo a factor of two lower than Orcus. [8] Should Vanth have an albedo of only 0.12, Vanth could be as large as 380 km (240 mi) with Orcus being 760 km (470 mi) in diameter. [7] The mass of Vanth also depends on its albedo and can vary from 3 to 9 percent of the total system mass. [7] [8] In 2016, Brown and Butler used resolved ALMA images and estimated Vanth's diameter at 480 km (300 mi), about half Orcus's diameter, making Orcus and Vanth a smaller analog of Pluto and Charon. [5] They also measured Vanth's albedo as only 0.08+0.02
    −0.01
    , almost 3 times darker than Orcus.

    For 7 March 2017, a stellar occultation by Orcus had been predicted to take place in the Americas and over the Pacific Ocean. Observations were made at five sites in North and South America, and two solid body chords were observed, with the more precise one being 434.4±2.4 km. Using speckle imaging, the occulted star was revealed to be a close double star, and a reconstruction of the orbits of Orcus and Vanth showed that both chords were from Vanth (occulting either of the two stars) rather than Orcus. A non-detection at a nearby site placed an upper limit of 442.5±10.2  km (274.9±6.3  mi ) on the diameter of Vanth. The occultation data is consistent with a pressure of at most 4 microbar for a global atmosphere of Vanth. [4]

    Vanth does not resemble other known collisional satellites because its spectrum is very different from that of its primary. Vanth may thus be a captured Kuiper belt object. [9] In that respect, it may be similar to the satellite of another possible dwarf planet, Gonggong, which also has a very different colour compared to its primary. [14]

    Notes

    1. Discovery announced on 22 February 2007. [1] [2]
    2. Calculated with the diameter of 442.5 km (radius 221.25 km) and assumed density of 0.8–1.5 g/cm3. [4] Assuming a spherical shape for Vanth, the radius of 221.25 km yields a volume of approximately 3.504×107 km3. Multiplying the volume with the densities of 0.8 g/cm3 or 1.5 g/cm3 yields the approximate masses of 3.6×1019 kg and 6.8×1019 kg.

    Related Research Articles

    Pluto Dwarf planet in the Kuiper belt of the Solar System

    Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It was the first and the largest Kuiper belt object to be discovered. After Pluto was discovered in 1930, it was declared to be the ninth planet from the Sun. Beginning in the 1990s, its status as a planet was questioned following the discovery of several objects of similar size in the Kuiper belt and the scattered disc, including the dwarf planet Eris. This led the International Astronomical Union (IAU) in 2006 to formally define the term "planet"—excluding Pluto and reclassifying it as a dwarf planet.

    28978 Ixion Plutino

    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.

    90482 Orcus Trans-Neptunian object and dwarf planet

    90482 Orcus, provisional designation 2004 DW, is a trans-Neptunian dwarf planet with a large moon, Vanth. It has a diameter of 910 km (570 mi). The surface of Orcus is relatively bright with albedo reaching 23 percent, neutral in color and rich in water ice. The ice is predominantly in crystalline form, which may be related to past cryovolcanic activity. Other compounds like methane or ammonia may also be present on its surface. Orcus was discovered by American astronomers Michael Brown, Chad Trujillo, and David Rabinowitz on 17 February 2004.

    Haumea Dwarf planet in the Solar System

    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 in the United States and disputably also in 2005 by a team headed by José Luis Ortiz Moreno at the Sierra Nevada Observatory in Spain, though the latter claim has been contested. On September 17, 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, though the uncertainty in best-fit modeling slightly overlaps with the larger size estimates for Makemake.

    38628 Huya Trans-Neptunian object

    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.

    Dysnomia (moon) moon of Eris

    Dysnomia (formally (136199) Eris I Dysnomia) is the only known moon of the dwarf planet Eris and likely the second-largest known moon of a dwarf planet, after Pluto I Charon. It was discovered in 2005 by Mike Brown and the laser guide star adaptive optics team at the W. M. Keck Observatory, and carried the provisional designation of S/2005 (2003 UB313) 1 until officially named Dysnomia (from the Ancient Greek word Δυσνομία meaning anarchy/lawlessness) after the daughter of the Greek goddess Eris.

    Moons of Pluto Natural satellite orbiting Pluto

    The dwarf planet Pluto has five natural satellites. In order of distance from Pluto, they are Charon, Styx, Nix, Kerberos, and Hydra. Charon, the largest, is mutually tidally locked with Pluto, and is massive enough that Pluto–Charon is sometimes considered a double dwarf planet.

    <span class="nowrap">(55636) 2002 TX<sub>300</sub></span>

    (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.

    Dwarf planet Planetary-mass object

    A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun – something smaller than any of the eight classical planets, but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to planetary geologists is that, being possibly differentiated and geologically active bodies, they may display planetary geology, an expectation borne out by the 2015 New Horizons mission to Pluto.

    <span class="nowrap">(208996) 2003 AZ<sub>84</sub></span>

    (208996) 2003 AZ84 is a trans-Neptunian object with a possible moon from 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.

    <span class="nowrap">(84922) 2003 VS<sub>2</sub></span> Trans-Neptunian object

    (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.

    120347 Salacia Possible dwarf planet

    120347 Salacia, provisional designation 2004 SB60, is a large planetoid in the Kuiper belt, approximately 850 kilometers in diameter. As of 2018, it is located 44.8 astronomical units from the Sun, and reaches apparent magnitude 20.7 at opposition.

    225088 Gonggong Dwarf planet in the scattered-disc

    225088 Gonggong (provisional designation: 2007 OR10) is a dwarf planet, 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 (5.1–15.1 billion kilometers; 3.2–9.4 billion miles) from the Sun. As of 2019, 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. 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.

    50000 Quaoar Cold classical Kuiper belt object

    50000 Quaoar, provisional designation 2002 LM60, is a dwarf planet in the Kuiper belt, a region of icy planetesimals beyond Neptune. A non-resonant object (cubewano), it measures approximately 1,121 km (697 mi) in diameter, about half the diameter of Pluto. The object was discovered by American astronomers Chad Trujillo and Michael Brown at the Palomar Observatory on 4 June 2002. Signs of water ice on the surface of Quaoar have been found, which suggests that cryovolcanism may be occurring on Quaoar. A small amount of methane is present on its surface, which can only be retained by the largest Kuiper belt objects. In February 2007, Weywot, a synchronous moon in orbit around Quaoar, was discovered by Brown. Weywot is measured to be 170 km (110 mi) across. Both objects were named after mythological figures from the Native American Tongva people in Southern California. Quaoar is the Tongva creator deity and Weywot is his son.

    Weywot Moon of dwarf planet 50000 Quaoar

    Weywot, officially (50000) Quaoar I Weywot, is the only known moon of the trans-Neptunian planetoid 50000 Quaoar. Discovered by Michael Brown and T.A. Suer using images acquired by the Hubble Space Telescope on 14 February 2006, its existence was announced in an IAU Circular notice published on 22 February 2007. Weywot has an estimated diameter of 170 km (110 mi). The satellite was found at 0.35 arcseconds from Quaoar with an apparent magnitude difference of 5.6.

    Planetary-mass moon Moons comparable in size to small planets

    A planetary-mass moon is a planetary-mass object that is also a natural satellite. They are large and ellipsoidal in shape. Two moons in the Solar System are larger than the planet Mercury : Ganymede and Titan, and seven are larger and more massive than the dwarf planet Pluto.

    Actaea (moon) Moon of 120347 Salacia

    Actaea, officially (120347)Salacia I Actaea, is a natural satellite of the classical Kuiper belt planetoid 120347 Salacia. Its diameter is estimated 300 km (190 mi), which is approximately one-third the diameter of Salacia; thus, Salacia and Actaea are viewed by some astronomers to be a binary system. Assuming that the following size estimates are correct, Actaea is about the sixth-biggest known moon of a trans-Neptunian object, after Charon (1212 km), Dysnomia (700 km), Vanth (443 km), Ilmarë (326 km) and Hiʻiaka (320 km), but possibly also Hiisi.

    Ilmarë Moon of 174567 Varda

    Ilmarë, or Varda I, full designation 174567 Varda I Ilmarë, is the single known natural satellite of the Kuiper Belt planetoid 174567 Varda. It was discovered by Keith Noll et al. in 2009, at a separation of about 0.12 arcsec, using discovery images taken by the Hubble Space Telescope on 26 April 2009, and reported in 2011. At approximately 326 km in diameter (about 45% that of its primary), it is the fourth or fifth-largest known moon of a trans-Neptunian object, after Pluto I Charon, Eris I Dysnomia, Orcus I Vanth and very possibly Haumea I Hiʻiaka. Assuming that Ilmarë has the same albedo and density as Varda, Ilmarë would constitute approximately 8.4% of the system mass, approximately 2.2×1019 kg.

    References

    1. 1 2 3 4 Daniel W. E. Green (22 February 2007). "IAUC 8812: Sats OF 2003 AZ_84, (50000), (55637),, (90482)". International Astronomical Union Circular. Retrieved 4 July 2011.
    2. 1 2 3 Wm. Robert Johnston (4 March 2007). "(90482) Orcus". Johnston's Archive. Archived from the original on 10 February 2009. Retrieved 26 March 2009.
    3. Grundy, W. M.; Noll, K. S.; Roe, H. G.; Buie, M. W.; Porter, S. B.; Parker, A. H.; Nesvorný, D.; Benecchi, S. D.; Stephens, D. C.; Trujillo, C. A. (2019). "Mutual Orbit Orientations of Transneptunian Binaries" (PDF). Icarus. doi:10.1016/j.icarus.2019.03.035. ISSN   0019-1035.
    4. 1 2 3 4 Sickafoose, A. A.; Bosh, A. S.; Levine, S. E.; Zuluaga, C. A.; Genade, A.; Schindler, K.; Lister, T. A.; Person, M. J. (February 2019). "A stellar occultation by Vanth, a satellite of (90482) Orcus". Icarus. 319: 657–668. arXiv: 1810.08977 . Bibcode:2019Icar..319..657S. doi:10.1016/j.icarus.2018.10.016.
    5. 1 2 3 Brown, Michael E.; Butler, Bryan J. (22 January 2018). "Medium-sized satellites of large Kuiper belt objects". The Astronomical Journal. 156 (4): 164. arXiv: 1801.07221 . doi:10.3847/1538-3881/aad9f2.
    6. 1 2 Ortiz, J. L.; Cikota, A.; Cikota, S.; Hestroffer, D.; Thirouin, A.; Morales, N.; Duffard, R.; Gil-Hutton, R.; Santos-Sanz, P.; De La Cueva, I. (2010). "A mid-term astrometric and photometric study of trans-Neptunian object (90482) Orcus". Astronomy & Astrophysics. 525: A31. arXiv: 1010.6187 . Bibcode:2011A&A...525A..31O. doi:10.1051/0004-6361/201015309.
    7. 1 2 3 4 5 Carry, B.; Hestroffer, D.; Demeo, F. E.; Thirouin, A.; Berthier, J.; Lacerda, P.; Sicardy, B.; Doressoundiram, A.; Dumas, C.; Farrelly, D.; Müller, T. G. (2011). "Integral-field spectroscopy of (90482) Orcus-Vanth". Astronomy & Astrophysics. 534: A115. arXiv: 1108.5963 . Bibcode:2011A&A...534A.115C. doi:10.1051/0004-6361/201117486.
    8. 1 2 3 4 5 6 7 Brown, M.E.; Ragozzine, D.; Stansberry, J.; Fraser, W.C. (2010). "The size, density, and formation of the Orcus-Vanth system in the Kuiper belt". The Astronomical Journal. 139 (6): 2700–2705. arXiv: 0910.4784 . Bibcode:2010AJ....139.2700B. doi:10.1088/0004-6256/139/6/2700.
    9. 1 2 3 4 Michael E. Brown (23 March 2009). "S/2005 (90482) 1 needs your help". Mike Brown's Planets (blog). Archived from the original on 28 March 2009. Retrieved 25 March 2009.
    10. 1 2 Michael E. Brown (6 April 2009). "Orcus Porcus". Mike Brown's Planets (blog). Archived from the original on 14 April 2009. Retrieved 6 April 2009.
    11. "Committee on Small Body Nomenclature: Names of Minor Planets" . Retrieved 8 April 2009.
    12. "The MINOR PLANET CIRCULARS/MINOR PLANETS AND COMETS" (PDF). Minorplanetcenter.org. 30 March 2010. Retrieved 12 October 2017.
    13. "Minor planet circular" (PDF). minorplanetcenter.org. 2010. Retrieved 8 August 2010.
    14. Kiss, C.; Marton, G.; Parker, A.; Grundy, W.; Farkas-Takács, A. I.; Stansberry, J.; Pal, A.; Müller, T. G.; Noll, K.; Schwamb, M. E.; Barr Mlinar, A. C.; Young, L. A.; Vinkó, J. (24 October 2018). The mass and density of the dwarf planet 2007 OR10. 50th annual meeting of the AAS Division of Planetary Sciences. abstract 311.02. Retrieved 21 September 2018.