Discovered byCINEOS
Discovery dateAugust 10, 2004
P/2004 PY42
Orbital characteristics A
Aphelion20.8 AU
Perihelion11.77 AU
(outside Saturn's orbit)
Semi-major axis16.28 AU
Orbital period65.67 yr
Max. orbital speed9.8 km/s
Min. orbital speed5.6 km/s (2033-Nov-30)
Dimensions66.17±22.9 km[4]
Nucleus albedo0.053±0.019
Last perihelionApril 24, 2001[1]
Next perihelion
  • March 18, 2066[2]
  • March 22, 2066[1]
  • March 23, 2066[3]

167P/CINEOS (P/2004 PY42) is a large periodic comet and active, grey centaur, approximately 66 kilometers (41 miles) in diameter, orbiting the Sun outside the orbit of Saturn in the Solar System. It was discovered on August 10, 2004, by astronomers with the CINEOS survey at Gran Sasso in Italy. It is one of only a handful known Chiron-type comets.

The comet nucleus (~66 km) is roughly half the size of C/2014 UN271 (Bernardinelli–Bernstein) and it has a similar perihelion point just outside the orbit of Saturn.

Large comets with perihelion near Saturn's orbit at 10 AU
Comet Nucleus
(Sun approach)
95P/Chiron 215 km 8.5 AU
C/2014 UN271 (Bernardinelli–Bernstein) 120 km 10.95 AU
167P/CINEOS 66 km 11.77 AU


Due to its high Jupiter tisserand of 3.5, and a semi-major axis larger than that of Jupiter, 167P/CINEOS is classified as a Chiron-type comet, named after the groups namesake, 2060 Chiron or 95P/Chiron, designated as both minor planet and comet.[4]

167P/CINEOS was first reported as a minor planet, designated 2004 PY42, but was found to have a very faint asymmetric cometary coma.[5] Contrary to Chiron, which is the prototype object for the dynamical group of centaurs, 167P/CINEOS has no "dual status" as comet and minor planet, and demonstrates the inconsistencies in applying the current rules for designating small Solar System bodies.[6] 167P/CINEOS not only has orbital parameters similar to those of Chiron, but also a low B–R magnitude of 1.29±0.03, which places it into the group grey centaurs.[7]

In June 2039, 167P/CINEOS will pass 1.64 AU from Uranus.[4]


  1. ^ a b "167P/CINEOS Orbit". Minor Planet Center. Retrieved June 18, 2014.
  2. ^ "Horizons Batch for 167P/CINEOS on 2066-Mar-18" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Retrieved June 24, 2022. (JPL#22 Soln.date: 2021-Apr-15)
  3. ^ Syuichi Nakano (June 18, 2005). "167P/CINEOS (2004 PY42) (NK 1185)". OAA Computing and Minor Planet Sections. Retrieved February 20, 2012.
  4. ^ a b c "JPL Small-Body Database Browser: 167P/CINEOS" (2011-10-19 last obs (arc=9.35 years)). Retrieved July 12, 2012.
  5. ^ Romanishin, W.; Tegler, S. C.; Boattini, A.; de Luise, F.; di Paola, A. (June 2005). "Comet C/2004 PY_42 (cineos)". International Astronomical Union Circular – Central Bureau for Astronomical Telegrams. 8545: 1. Bibcode:2005IAUC.8545....1R. ISSN 0081-0304.
  6. ^ Green, D. W. E. (June 2005). "Comets 165P/2000 B4, 166P/2001 T4, and 167P/2004 PY_42". International Astronomical Union Circular – Central Bureau for Astronomical Telegrams. 8552: 2. Bibcode:2005IAUC.8552....2G. ISSN 0081-0304.
  7. ^ Tegler, S. C.; Romanishin, W.; Consolmagno, G. J.; J., S. (December 2016). "Two Color Populations of Kuiper Belt and Centaur Objects and the Smaller Orbital Inclinations of Red Centaur Objects". The Astronomical Journal. 152 (6): 210. Bibcode:2016AJ....152..210T. doi:10.3847/0004-6256/152/6/210. ISSN 0004-6256.
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