page_title: Centaur (small Solar System body)
section_title: Similarities to comets
hierarchical_section_title: Centaur (small Solar System body) / Physical characteristics / Similarities to comets
caption_attribution_description: The orbit of comet 38P/Stephan-Oterma. Between the years 1982 and 2067, this object will make close approaches to the giant planets Jupiter, Saturn, and Uranus.
context_page_description: A centaur, in planetary astronomy, is a small Solar System body with either a perihelion or a semi-major axis between those of the outer planets. Centaurs generally have unstable orbits because they cross or have crossed the orbits of one or more of the giant planets; almost all their orbits have dynamic lifetimes of only a few million years, but there is one centaur, 514107 Kaʻepaokaʻawela, which may be in a stable orbit. They are named after the mythological centaurs that were a mixture of horse and human. Observational bias toward large objects makes determination of the total centaur population difficult. Estimates for the number of centaurs in the Solar System more than 1 km in diameter range from as low as 44,000 to more than 10,000,000
  The first centaur to be discovered, under the definition of the Jet Propulsion Laboratory and the one used here, was 944 Hidalgo in 1920. However, they were not recognized as a distinct population until the discovery of 2060 Chiron in 1977. The largest confirmed centaur is 10199 Chariklo, which at 260 kilometers in diameter is as big as a mid-sized main-belt asteroid, and is known to have a system of rings. It was discovered in 1997.
context_section_description: Observations of Chiron in 1988 and 1989 near its perihelion found it to display a coma (a cloud of gas and dust evaporating from its surface). It is thus now officially classified as both a comet and an asteroid, although it is far larger than a typical comet and there is some lingering controversy. Other centaurs are being monitored for comet-like activity: so far two, 60558 Echeclus, and 166P/NEAT have shown such behavior. 166P/NEAT was discovered while it exhibited a coma, and so is classified as a comet, though its orbit is that of a centaur. 60558 Echeclus was discovered without a coma but recently became active, and so it too is now classified as both a comet and an asteroid. Overall, there are ~30 centaurs for which activity has been detected, with the active population biased toward objects with smaller perihelion distances.  
  Carbon monoxide has been detected in 60558 Echeclus 
  and Chiron in very small amounts, and the derived CO production rate was calculated to be sufficient to account for the observed coma. The calculated CO production rate from both 60558 Echeclus and Chiron is substantially lower than what is typically observed for 29P/Schwassmann–Wachmann, another distantly active comet often classified as a centaur.
  There is no clear orbital distinction between centaurs and comets. Both 29P/Schwassmann-Wachmann and 39P/Oterma have been referred to as centaurs since they have typical centaur orbits. The comet 39P/Oterma is currently inactive and was seen to be active only before it was perturbed into a centaur orbit by Jupiter in 1963. The faint comet 38P/Stephan–Oterma would probably not show a coma if it had a perihelion distance beyond Jupiter's orbit at 5 AU.  By the year 2200, comet 78P/Gehrels will probably migrate outwards into a centaur-like orbit.
caption: Comet 38P exhibits centaur-like behavior by making close approaches to Jupiter, Saturn, and Uranus between 1982 and 2067.[33]
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