167P/CINEOS
A large, active grey centaur and Chiron-type comet.
167P/CINEOS, also designated P/2004 PY42, is a large periodic comet and active grey centaur with a diameter of about 66 kilometers. It orbits the Sun beyond Saturn’s orbit and was discovered on August 10, 2004, by the CINEOS survey at Italy’s Gran Sasso observatory. The comet is one of the few known Chiron-type comets, and its nucleus is roughly half the size of C/2014 UN271 (Bernardinelli–Bernstein), with a similar perihelion just outside Saturn’s orbit.
Because its high Jupiter Tisserand parameter (3.5) and semi-major axis exceed Jupiter’s, 167P/CINEOS is classified as a Chiron-type comet, named after 2060 Chiron (95P/Chiron), which holds dual status as both a minor planet and a comet. Initially reported as a minor planet (2004 PY42), 167P/CINEOS was later found to have a faint, asymmetric cometary coma. Unlike Chiron, however, it lacks dual status, highlighting inconsistencies in the current naming rules for small Solar System bodies. Its orbital parameters resemble Chiron’s, and its low B–R magnitude of 1.29±0.03 places it among the grey centaurs. In June 2039, it will pass 1.64 AU from Uranus.
Quick Facts
- Discoverer
- CINEOS
- Discovery Date
- August 10, 2004
- Designations
- P/2004 PY · 42
- Orbit Ref
- jpldata · MPC
- Epoch
- 2066-03-11
- Observation Arc
- 9.35 years
- Semimajor
- 16.28 AU
- Perihelion
- 11.77 AU / (outside Saturn's orbit)
- Aphelion
- 20.8 AU
- Eccentricity
- 0.27705
- Inclination
- 19.0529°
- Max Speed
- 9.8 km/s
Facts from the source article.
Lore & Background
167P/CINEOS was first reported as a minor planet, designated 2004 PY42, but was found to have a very faint asymmetric cometary coma. 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, demonstrating inconsistencies in the current rules for designating small Solar System bodies. Its orbital parameters are similar to those of Chiron, and it has a low B–R magnitude of 1.29±0.03, placing it into the group of grey centaurs.
Reader's Guide
167P/CINEOS is significant as one of the few known Chiron-type comets, a class defined by a high Jupiter tisserand of 3.5 and a semi-major axis larger than that of Jupiter. Its discovery and classification highlight inconsistencies in the rules for designating small Solar System bodies, as it lacks the dual comet–minor planet status that Chiron holds. The comet's nucleus, roughly 66 km in diameter, is about half the size of C/2014 UN271 (Bernardinelli–Bernstein) and shares a similar perihelion point just outside Saturn's orbit. Its grey color, indicated by a low B–R magnitude, and its active coma make it a valuable object for studying centaur activity and the transition between asteroid and comet behavior. In June 2039, it will pass 1.64 AU from Uranus, offering a future observation opportunity.
More in Periodic Comets 1-24
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