5145 Pholus


5145 Pholus is a Centaur (minor planetoid) of the solar system running in a stretched orbit, with a perihelion (closest approach to the Sun) less than Saturn's and aphelion (farthest approach from the Sun) farther than Neptune's. Close approaches of the object are not common: it has not come within one astronomical unit (about 150 million km) of a planet since 764 BC, and will not again until 5290. Astronomers think that Pholus started out as a Kuiper belt object.

5145 Pholus
Discovered bySpacewatch
(David L. Rabinowitz)
Discovery dateJanuary 9, 1992
1992 AD
Centaur, Asteroid
Orbital characteristics[1]
Epoch November 30, 2008 (JD 2454800.5)
Aphelion4784.1 Gm
(31.98 AU)
Perihelion1305.9 Gm
(8.730 AU)
3045.2 Gm
(20.356 AU)
33547.41 d
(91.85 yr)
6.01 km/s
Physical characteristics
Dimensions185±16 km [2]
Mass~6.6×1018 kg
Mean density
2.0? g/cm³ (assumed)
~0.052 m/s²
~0.098 km/s
9.98 hours[1]
Temperature~62 K
Spectral type
(red) B-V=1.19; V-R=0.78 [3]

It was found 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 to follow the tradition of naming this class of outer planet crossing objects after Centaurs.

Pholus was the second Centaur type asteroid to be found and was quickly found to be very red in color. Because it's very red, it is sometimes called "Big Red". Astronomers think the color is because of organic compounds on its surface.[4]

Unlike the first Centaur, 2060 Chiron, Pholus has shown no signs of cometary activity.

Astronomers think that Pholus' diameter is about 185±16 km.[2]


  1. 1.0 1.1 1.2 "JPL Small-Body Database Browser: 5145 Pholus (1992 AD)". May 27, 2008. Retrieved September 1, 2008.
  2. 2.0 2.1 Astronomy Abstract Service
  3. Tegler, Stephen C. (January 26, 2006). "Kuiper Belt Object Magnitudes and Surface Colors". Retrieved November 5, 2006.
  4. Wilson PD, Sagan C, Thompson WR (1994). "The organic surface of 5145 Pholus: constraints set by scattering theory". Icarus. 107 (2): 288–303. doi:10.1006/icar.1994.1024. PMID 11539180.{{cite journal}}: CS1 maint: multiple names: authors list (link)

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