5145 Pholus

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5145 Pholus
Discovery [1][2]
Discovered by Spacewatch
Discovery site Kitt Peak National Obs.
Discovery date 9 January 1992
MPC designation (5145) Pholus
Pronunciation /ˈfləs/ (foe'-ləs)
Named after
(Greek mythology)[3]
1992 AD
centaur[1] · distant[2]
Saturn crosser
Uranus crosser
Neptune crosser
Orbital characteristics[1]
Epoch 31 July 2016 (JD 2457600.5)
Uncertainty parameter 1
Observation arc 31.74 yr (11,593 days)
Aphelion 32.038 AU
Perihelion 8.7184 AU
20.378 AU
Eccentricity 0.5722
91.99 yr (33,601 days)
6.01 km/s
0° 0m 38.52s / day
Inclination 24.705°
Jupiter MOID 3.469 AU
TJupiter 3.20
Physical characteristics
Dimensions 99±15 km[4]
165.03 km (derived)[5]
185±16 km[6]
190 km[1][7]
9.977 h[8]
9.980 h[1][7]
9.982 h[9]
9.983 h[10]
0.057 (assumed)[5]
Tholen = Z [1] · C[5]
RR[11] · RR-U[12]
7.198±0.056 (R)[14]

5145 Pholus (/ˈfləs/; from Φόλος) provisional designation 1992 AD, is an eccentric centaur in the outer Solar System, approximately 180 kilometers in diameter, that crosses the orbit of both Saturn and Neptune. It was discovered on 9 January 1992, by American astronomer David L. Rabinowitz (unaccredited) of UA's Spacewatch survey at Kitt Peak National Observatory, and named after the mythological creature Pholus.[2]

Orbit and classification[edit]

Orbital diagram of 5145 Pholus

Pholus was the second centaur to be discovered.[19] Centaurs are objects in between the asteroid and trans-Neptunian populations of the Solar System – that is, beyond Jupiter's and within Neptune's orbit – which behave with characteristics of both asteroids and comets.

It orbits the Sun at a distance of 8.7–32.0 AU once every 91 years and 12 months (33,601 days; semi-major axis of 20.4 AU). Its orbit has an eccentricity of 0.57 and an inclination of 25° with respect to the ecliptic.[1]

A first precovery was taken at the Australian Siding Spring Observatory in 1977, extending the centaur's observation arc by 15 years prior to its discovery.[2] Pholus has not come within one astronomical unit of a planet since 764 BC, and will not until 5290.[20] It is believed that Pholus originated in the Kuiper belt.

Physical characteristics[edit]

Spectral type and color[edit]

After its discovery, Pholus was quickly found to be quite red in color, for which it has been occasionally nicknamed "Big Red". The color has been speculated to be due to organic compounds on its surface.[19] It is classified as a Z class object on the Tholen taxonomic scheme.[1]

The object has been classified by astronomers as RR and RR-U type, respectively.[11][12] Polarimetric observations with ESO's Very Large Telescope in 2007 and 2008, revealed noticeable negative polarization at certain phase angles, distinctly different from that of trans-Neptunian objects. Pholus appears to have a rather homogeneous surface with small amount of water frost on its darker parts.[12]

The surface composition of Pholus has been estimated from its reflectance spectrum using two spatially segregated components:[21] dark amorphous carbon and an intimate mixture of water ice, methanol ice, olivine grains, and complex organic compounds (tholins). The carbon black component was used to match the low albedo of the object. Unlike Chiron, Pholus has shown no signs of cometary activity.

Diameter and albedo[edit]

Diameter estimates range from 99 to 190 kilometers with a corresponding albedo between 0.155 and 0.04.[4][5][6][7]


This minor planet was named by the Minor Planet Names Committee for the creature Pholus, a centaur from Greek mythology, like his brother Chiron, after which 2060 Chiron was named, in order to follow the tradition of naming this class of outer planet-crossing objects after centaurs. Pholus died by a self-inflicted wound from a poisoned arrow used by Heracles (see 5143 Heracles), who buried Pholus on the mountain Pholoe.[3] The official naming citation was published by the Minor Planet Center on 14 July 1992 (M.P.C. 20523).[22]


  1. ^ a b c d e f g h i j "JPL Small-Body Database Browser: 5145 Pholus (1992 AD)" (2009-04-18 last obs.). Jet Propulsion Laboratory. Retrieved 16 November 2016.
  2. ^ a b c d "5145 Pholus (1992 AD)". Minor Planet Center. Retrieved 16 November 2016.
  3. ^ a b Schmadel, Lutz D. (2007). Dictionary of Minor Planet Names – (5145) Pholus. Springer Berlin Heidelberg. p. 443. ISBN 978-3-540-00238-3. Retrieved 16 November 2016.
  4. ^ a b c d Duffard, R.; Pinilla-Alonso, N.; Santos-Sanz, P.; Vilenius, E.; Ortiz, J. L.; Mueller, T.; et al. (April 2014). ""TNOs are Cool": A survey of the trans-Neptunian region. XI. A Herschel-PACS view of 16 Centaurs" (PDF). Astronomy and Astrophysics. 564: 17. arXiv:1309.0946. Bibcode:2014A&A...564A..92D. doi:10.1051/0004-6361/201322377. Retrieved 16 November 2016.
  5. ^ a b c d e "LCDB Data for (5145) Pholus". Asteroid Lightcurve Database (LCDB). Retrieved 16 November 2016.
  6. ^ a b "Infrared Observations of Distant Asteroids". Adsabs.harvard.edu. Retrieved 2013-10-30.
  7. ^ a b c d e f Tegler, S. C.; Romanishin, W.; Consolmagno, G. J.; Rall, J.; Worhatch, R.; Nelson, M.; et al. (June 2005). "The period of rotation, shape, density, and homogeneous surface color of the Centaur 5145 Pholus". Icarus. 175 (2): 390–396. Bibcode:2005Icar..175..390T. doi:10.1016/j.icarus.2004.12.011. Retrieved 16 November 2016.
  8. ^ Hoffmann, M.; Fink, U.; Grundy, W. M.; Hicks, M. (December 1991). "Photometric and spectroscopic observations of 5145 1992 AD". Observations and Physical Properties of Small Solar System Bodies: 203. Bibcode:1992LIACo..30..203H. Retrieved 16 November 2016.
  9. ^ Farnham, Tony L. (August 2001). "The Rotation Axis of the Centaur 5145 Pholus". Icarus. 152 (2): 238–245. Bibcode:2001Icar..152..238F. doi:10.1006/icar.2001.6656. Retrieved 16 November 2016.
  10. ^ Buie, Marc W.; Bus, Schelte J. (December 1992). "Physical observations of (5145) Pholus". Icarus. 100 (2): 288–294. Bibcode:1992Icar..100..288B. doi:10.1016/0019-1035(92)90101-C. Retrieved 16 November 2016.
  11. ^ a b c Perna, D.; Barucci, M. A.; Fornasier, S.; DeMeo, F. E.; Alvarez-Candal, A.; Merlin, F.; et al. (February 2010). "Colors and taxonomy of Centaurs and trans-Neptunian objects". Astronomy and Astrophysics. 510. arXiv:0912.2621. Bibcode:2010A&A...510A..53P. doi:10.1051/0004-6361/200913654. Retrieved 16 November 2016.
  12. ^ a b c Belskaya, Irina N.; Barucci, Maria A.; Fulchignoni, Marcello; Dovgopol, Anatolij N. (April 2015). "Updated taxonomy of trans-neptunian objects and centaurs: Influence of albedo". Icarus. 250: 482–491. Bibcode:2015Icar..250..482B. doi:10.1016/j.icarus.2014.12.004. Retrieved 16 November 2016.
  13. ^ "AstDys (5145) Pholus Ephemerides". Department of Mathematics, University of Pisa, Italy. Retrieved 16 November 2016.
  14. ^ Peixinho, N.; Delsanti, A.; Guilbert-Lepoutre, A.; Gafeira, R.; Lacerda, P. (October 2012). "The bimodal colors of Centaurs and small Kuiper belt objects". Astronomy and Astrophysics. 546: 12. arXiv:1206.3153. Bibcode:2012A&A...546A..86P. doi:10.1051/0004-6361/201219057. Retrieved 16 November 2016.
  15. ^ Romanishin, W.; Tegler, S. C. (March 1999). "Rotation rates of Kuiper-belt objects from their light curves". Nature. 398 (6723): 129–132.(NatureHomepage). Bibcode:1999Natur.398..129R. doi:10.1038/18168. Retrieved 16 November 2016.
  16. ^ Romanishin, W.; Tegler, S. C. (December 2005). "Accurate absolute magnitudes for Kuiper belt objects and Centaurs". Icarus. 179 (2): 523–526. Bibcode:2005Icar..179..523R. doi:10.1016/j.icarus.2005.06.016. Retrieved 16 November 2016.
  17. ^ Davies, John K.; McBride, Neil; Ellison, Sara L.; Green, Simon F.; Ballantyne, David R. (August 1998). "Visible and Infrared Photometry of Six Centaurs". Icarus. 134 (2): 213–227. Bibcode:1998Icar..134..213D. doi:10.1006/icar.1998.5931. Retrieved 16 November 2016.
  18. ^ Belskaya, I. N.; Bagnulo, S.; Barucci, M. A.; Muinonen, K.; Tozzi, G. P.; Fornasier, S.; et al. (November 2010). "Polarimetry of Centaurs (2060) Chiron, (5145) Pholus and (10199) Chariklo". Icarus. 210 (1): 472–479. Bibcode:2010Icar..210..472B. doi:10.1016/j.icarus.2010.06.005. Retrieved 16 November 2016.
  19. ^ a b Wilson, P. D.; Sagan, C.; Thompson, W. R. (February 1994). "The organic surface of 5145 Pholus: Constraints set by scattering theory". Icarus. 107 (2): 288–303. Bibcode:1994Icar..107..288W. doi:10.1006/icar.1994.1024. Retrieved 16 November 2016.
  20. ^ "Fifty clones of Centaur 5145 Pholus all passing within ~100Gm of Neptune on 5290-07-07". Retrieved 2009-04-23. (Solex 10)
  21. ^ Cruikshank DP; et al. (1998). "The Composition of Centaur 5145 Pholus". Icarus. 135 (2): 389–407. Bibcode:1998Icar..135..389C. doi:10.1006/icar.1998.5997.
  22. ^ "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 16 November 2016.

External links[edit]