5145 Pholus

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5145 Pholus
5145 Pholus.tiff
Orbital diagram (top view)
Discovered by Spacewatch
(David Rabinowitz)
Discovery date 9 January 1992
Named after
1992 AD
Saturn crosser
Uranus crosser
Neptune crosser
Orbital characteristics[1]
Epoch JD 2454800.5 (30 November 2008)
Aphelion 31.98 AU (Q)
4,784 Gm
Perihelion 8.730 AU (q)
1305 Gm
20.356 AU (a)
3045.2 Gm
Eccentricity 0.5711
91.85 yr
33547.41 d
6.01 km/s
Inclination 24.65°
Physical characteristics
Dimensions 185±16 km[2]
9.98 hours[1]
Albedo 0.046±0.02
Temperature ~ 62 K
Spectral type
(red) B−V=1.19;
~ 20.7[4]

5145 Pholus (/ˈfləs/; from Greek: Φόλος) is a centaur in an eccentric orbit, with a perihelion less than Saturn's and aphelion greater than Neptune's. Pholus has not come within one astronomical unit of a planet since 764 BC, and will not until 5290.[5] It is believed that Pholus originated in the Kuiper belt.

It was discovered by David L. Rabinowitz, then of the University of Arizona's Spacewatch Project, and named after Pholus, the brother of the mythological 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 was the second centaur to be discovered and 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.[6]

The surface composition of Pholus has been estimated from its reflectance spectrum using two spatially segregated components:[7] 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 2060 Chiron, Pholus has shown no signs of cometary activity.

The diameter of Pholus is estimated to be 185±16 km.[2]


  1. ^ a b c "JPL Small-Body Database Browser: 5145 Pholus (1992 AD)" (2008-05-27 last obs). Retrieved 2008-09-01. 
  2. ^ a b "Infrared Observations of Distant Asteroids". Adsabs.harvard.edu. Retrieved 2013-10-30. 
  3. ^ Tegler, Stephen C. (2006-01-26). "Kuiper Belt Object Magnitudes and Surface Colors". Retrieved 2006-11-05. 
  4. ^ "AstDys (5145) Pholus Ephemerides". Department of Mathematics, University of Pisa, Italy. Retrieved 2010-06-28. 
  5. ^ "Fifty clones of Centaur 5145 Pholus all passing within ~100Gm of Neptune on 5290-07-07". Retrieved 2009-04-23.  (Solex 10)
  6. ^ Wilson PD; Sagan C; Thompson WR (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. PMID 11539180. 
  7. ^ 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. 

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