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2004 XR190, nicknamed Buffy, is a trans-Neptunian object, classified both as scattered and detached object, located in the outermost region of the Solar System. It was first observed on 11 December 2004, by astronomers with the Canada–France Ecliptic Plane Survey at the Mauna Kea Observatories, Hawaii, United States.[1][2] The highly inclined dwarf planet candidate measures approximately 550 kilometers (340 miles) in diameter. With its perihelion of 51 AU, it belongs to a small and poorly understood group of very distant objects with moderate eccentricities.[9]

2004 XR190
2004-xr190 hst.jpg
Hubble Space Telescope image of 2004 XR190, taken on October 2010
Discovery [1][2]
Discovered byCFEPS
Discovery siteMauna Kea Obs.
(first observed only)
Discovery date11 December 2004
MPC designation2004 XR190
Buffy (nickname)[3]
TNO[4] · detached[5][6]
SDO[7] · distant[1]
Orbital characteristics[4]
Epoch 27 April 2019 (JD 2458600.5)
Uncertainty parameter 3
Observation arc14.74 yr (5,383 d)
Aphelion63.401 AU
Perihelion51.110 AU
57.255 AU
433.24 yr (158,242 d)
0° 0m 8.28s / day
Physical characteristics
Mean diameter
335–530 km[8]
425–850 km[9]
561 km[10]
612 km[7]
0.09 (assumed)[7][10]


Discovery and namingEdit

Buffy was discovered on 11 December 2004.[1] It was discovered by astronomers led by Rhiannon Allen (Lynne Jones) of the University of British Columbia as part of the Canada–France Ecliptic Plane Survey (CFEPS) using the Canada–France–Hawaii Telescope (CFHT) near the ecliptic. The team included Brett Gladman, John Kavelaars, Jean-Marc Petit, Joel Parker and Phil Nicholson.[2] In 2015, six precovery images from 2002 and 2003 were found in Sloan Digital Sky Survey data.

The object was nicknamed "Buffy" by the discovery team, after the fictional vampire slayer Buffy Summers, and proposed several Inuit-based official names to the International Astronomical Union.[3]

Orbit and classificationEdit

Buffy is located in the "gap", a poorly understood region.

Buffy orbits the Sun at a distance of 51.1–63.4 AU once every 433 years and 3 months (158,242 days; semi-major axis of 57.26 AU). Its orbit has a moderate eccentricity of 0.11 and a high inclination of 47° with respect to the ecliptic.[4]

It belongs to the same group as 2014 FC72, 2014 FZ71, 2015 FJ345 and 2015 KQ174 (also see diagram), that are poorly understood for their large perihelia combined with moderate eccentricities. Considered a scattered and detached object,[5][6][7] Buffy is particularly unusual as it has an unusually circular orbit for a scattered-disc object (SDO). Although it is thought that traditional scattered-disc objects have been ejected into their current orbits by gravitational interactions with Neptune, the low eccentricity of its orbit and the distance of its perihelion (SDOs generally have highly eccentric orbits and perihelia less than 38 AU) seems hard to reconcile with such celestial mechanics. This has led to some uncertainty as to the current theoretical understanding of the outer Solar System. The theories include close stellar passages, unseen planet/rogue planets/planetary embryos in the early Kuiper belt, and resonance interaction with an outward-migrating Neptune. The Kozai mechanism is capable of transferring orbital eccentricity to a higher inclination.[9]

The object is also the largest possible dwarf planet that has an inclination larger than 45°,[12] traveling further "up and down" than "left to right" around the Sun when viewed edge-on along the ecliptic.

Most distant objectsEdit

Buffy came to aphelion around 1901.[13] Other than long-period comets, it is currently about the thirteenth-most-distant known large body (57.5 AU) in the Solar System with a well-known orbit, after Eris and Dysnomia (96.3 AU), 2007 OR10 (87.4 AU), Sedna (85.9 AU), 2014 FC69 (84.0 AU), 2006 QH181 (83.3 AU), 2012 VP113 (83.3 AU), 2013 FY27 (80.3 AU), 2010 GB174 (70.5 AU), 2000 CR105 (60.3 AU), 2003 QX113 (59.8 AU), and 2008 ST291 (59.6 AU).[3][14]

Physical characteristicsEdit

With an estimated albedo between 0.04 and 0.25, Buffy has a diameter of 335 to 850 kilometers, roughly a quarter the size of Pluto.[7][8][9][10]

On his website, American astronomer Michael Brown lists Buffy as a "likely" dwarf planet (500–600 km), which is the category with the 3rd highest certainty in his 5-class taxonomic system.[10] As of 2018, no spectral type and color indices, nor a rotational lightcurve have been obtained from spectroscopic and photometric observations. The body's color, rotation period, pole and shape remain unknown.[4]


See alsoEdit


  1. ^ a b c d e "2004 XR190". Minor Planet Center. Retrieved 13 December 2018.
  2. ^ a b c "MPEC 2005-X72 : 2004 XR190". IAU Minor Planet Center. 12 December 2005. Retrieved 13 December 2018. (K04XJ0R)
  3. ^ a b c Maggie McKee. "Strange new object found at edge of Solar System". New Scientist. Retrieved 13 December 2018.
  4. ^ a b c d e "JPL Small-Body Database Browser: (2004 XR190)" (2017-09-01 last obs.). Jet Propulsion Laboratory. Retrieved 13 December 2018.
  5. ^ a b Jewitt, David, Morbidelli, Alessandro, & Rauer, Heike. (2007). Trans-Neptunian Objects and Comets: Saas-Fee Advanced Course 35. Swiss Society for Astrophysics and Astronomy. Berlin: Springer. ISBN 3-540-71957-1.
  6. ^ a b Lykawka, Patryk Sofia; Mukai, Tadashi (July 2007). "Dynamical classification of trans-neptunian objects: Probing their origin, evolution, and interrelation". Icarus. 189 (1): 213–232. Bibcode:2007Icar..189..213L. doi:10.1016/j.icarus.2007.01.001. Retrieved 13 December 2018.
  7. ^ a b c d e Johnston, Wm. Robert (7 October 2018). "List of Known Trans-Neptunian Objects". Johnston's Archive. Retrieved 13 December 2018.
  8. ^ a b c Schaller, E. L.; Brown, M. E. (April 2007). "Volatile Loss and Retention on Kuiper Belt Objects" (PDF). The Astrophysical Journal. 659 (1): I.61–I.64. Bibcode:2007ApJ...659L..61S. doi:10.1086/516709. Retrieved 13 December 2018.
  9. ^ a b c d e Allen, R. L.; Gladman, B.; Kavelaars, J. J.; Petit, J.-M.; Parker, J. W.; Nicholson, P. (March 2006). "Discovery of a Low-Eccentricity, High-Inclination Kuiper Belt Object at 58 AU" (PDF). The Astrophysical Journal. 640 (1): L83–L86. arXiv:astro-ph/0512430. Bibcode:2006ApJ...640L..83A. doi:10.1086/503098. Retrieved 13 December 2018. (Discovery paper)
  10. ^ a b c d Brown, Michael E. "How many dwarf planets are there in the outer solar system?". California Institute of Technology. Retrieved 13 December 2018.
  11. ^ "2004 XR190 – Ephemerides". AstDyS-2, Asteroids – Dynamic Site, Department of Mathematics, University of Pisa, Italy. Retrieved 13 December 2018.
  12. ^ "JPL Small-Body Database Search Engine: H < 6.5 (mag)". JPL Solar System Dynamics. Retrieved 27 March 2014.
  13. ^ "Horizon Online Ephemeris System". California Institute of Technology, Jet Propulsion Laboratory. Retrieved 23 March 2009.
  14. ^ "List of minor planets more than 57.0 AU from the Sun". AstDyS-2, Asteroids – Dynamic Site, Department of Mathematics, University of Pisa, Italy. Retrieved 13 December 2018.

External linksEdit