5145 Pholus

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5145 Pholus
Discovered by Spacewatch
(David L. Rabinowitz)
Discovery time January 9, 1992
Other names 1992 AD
Group Centaur, Asteroid
Reference date November 30, 2008 (JD 2454800.5)
Longest distance from the Sun 4784.1 Gm
(31.98 AU)
Shortest distance from the Sun 1305.9 Gm
(8.730 AU)
Longest distance from the center of its orbital path
("semi-major axis")
3045.2 Gm
(20.356 AU)
How egg-shaped its orbit is
How long it takes to complete an orbit 33547.41 d
(91.85 yr)
Average speed 6.01 km/s
Mean anomaly 67.49°
Angle above the reference plane
Longitude of where it comes up through the reference plane 119.44°
Angle between its shortest distance from what it orbits around and where it comes up through the reference plane
("argument of periapsis")
Size and Other Qualities
Measures 185±16 km [2]
Mass ~6.6×1018 kg
Average density 2.0? g/cm³ (assumed)
Gravity at its surface ~0.052 m/s²
Slowest speed able to escape into space
("escape velocity")
~0.098 km/s
How long it takes to turn around one time 9.98 hours[1]
How much light it reflects 0.046±0.02
Avg. surface temp. ~62 K
Light-band group
("spectral type")
(red) B-V=1.19; V-R=0.78 [3]
True brightness
("absolute magnitude")

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.

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]

References[change | change source]

  1. 1.0 1.1 1.2 "JPL Small-Body Database Browser: 5145 Pholus (1992 AD)". 2008-05-27 last obs. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Pholus. Retrieved 2008-09-01.
  2. 2.0 2.1 Astronomy Abstract Service
  3. Tegler, Stephen C. (2006-01-26). "Kuiper Belt Object Magnitudes and Surface Colors". http://www.physics.nau.edu/~tegler/research/survey.htm. Retrieved 2006-11-05.
  4. Wilson PD, Sagan C, Thompson WR (1994). "The organic surface of 5145 Pholus: constraints set by scattering theory". Icarus 107: 288–303. doi:10.1006/icar.1994.1024. PMID 11539180.

Other websites[change | change source]