Editing 2060 Chiron (section)

== Physical characteristics ==

=== Spectral type ===

The visible and near-[[infrared]] spectrum of Chiron is neutral,<ref name="Campins-1994" /> and is similar to that of [[C-type asteroid]]s and the nucleus of [[Halley's Comet]].<ref name="Luu-1990b" /> The near-infrared spectrum of Chiron shows absence of water ice.<ref name="Luu-2000" />

=== Rotation period ===

Four rotational [[light curve]]s of ''Chiron'' were taken from [[Photometry (astronomy)|photometric]] observations between 1989 and 1997. Lightcurve analysis gave a concurring, well-defined [[rotational period]] of 5.918 hours with a small brightness variation of 0.05 to 0.09 [[Magnitude (astronomy)|magnitude]], which indicates that the body has a rather spheroidal shape ({{small|[[LCDB quality code|U=3/3/3]]}}).<ref name="lcdb" /><ref name="Bus-1989"/><ref name="Luu-1990b" /><ref name="Marcialis-1993" /><ref name="Lazzaro-1997" />

=== Diameter ===

{| class="wikitable" style="text-align:center; font-size: 0.9em; margin-left: 0.7em;" align=right
|+ Summary – size estimates for Chiron:
!Year !! Diameter !! Notes !! Refs
|-
| 1984 || 180&nbsp;km || align=left | Lebofsky (1984) || <ref name="Groussin-2004" />
|-
| 1991 || 186&nbsp;km || align=left | [[IRAS]] || <ref name="Groussin-2004" />
|-
| 1994 || 188&nbsp;km || align=left | Campins (radius {{val|94|6}}&nbsp;km)|| <ref name="Campins-1994" />
|-
| 1996 || 180&nbsp;km || align=left | [[Occultation#Occultations by asteroids|occultation]] || <ref name="Groussin-2004" />
|-
| 1998 || 166&nbsp;km || align=left | Dunham occultation list<br />(Dunham 1998) || <ref name="jpldata" />
|-
| 2007 || 233&nbsp;km || align=left | [[Spitzer Space Telescope]] || <ref name="Stansberry-2007" />
|-
| 2013 || 218&nbsp;km || align=left | [[Herschel Space Observatory]]<br />{{small|(PACS and SPIRE)}} || <ref name="Fornasier-2013" />
|-
| 2017 || 271&nbsp;km || align=left | LCDB || <ref name="lcdb" />
|-
| 2023 || 196&nbsp;km || align=left | Sickafoose || <ref name="Sickafoose2023"/>
|}

The assumed size of an object depends on its [[Absolute magnitude#Solar System bodies (H)|absolute magnitude]] (H) and the [[albedo]] (the amount of light it reflects). In 1984 Lebofsky estimated Chiron to be about 180&nbsp;km in diameter.<ref name="Groussin-2004" /> Estimates in the 1990s were closer to 150&nbsp;km in diameter.<ref name="jpldata" /><ref name="Groussin-2004"/> [[Occultation#Occultations by asteroids|Occultation]] data from 1993 suggests a diameter of about 180&nbsp;km.<ref name="Groussin-2004" /> Combined data from the [[Spitzer Space Telescope]] in 2007 and the Herschel Space Observatory in 2011 suggests that Chiron is {{nowrap|{{val|218|20}} km}} in diameter.<ref name="Fornasier-2013" /> Therefore, Chiron may be as large as [[10199 Chariklo]].<ref name="Stansberry-2007" /> The diameter of Chiron is difficult to estimate in part because the true absolute magnitude of its nucleus is uncertain due to its highly variable cometary activity.<ref name="Fornasier-2013" />

=== Cometary behavior ===

In February 1988, at 12&nbsp;AU from the Sun, Chiron brightened by 75 percent.<ref name="hartmann1990" /> This is behavior typical of comets but not asteroids. Further observations in April 1989 showed that Chiron had developed a cometary [[coma (cometary)|coma]],<ref name="meech1989" /> A tail was detected in 1993.<ref name="Campins-1994" /> Chiron differs from other comets in that [[water]] is not a major component of its coma, because it is too far from the [[Sun]] for water to sublimate.<ref name="Meech90" /> In 1995 [[carbon monoxide]] was detected in Chiron in very small amounts, and the derived CO production rate was calculated to be sufficient to account for the observed coma.<ref name="womack1999" /> [[Cyanide]] was also detected in the spectrum of Chiron in 1991.<ref name="Bus91" /> At the time of its discovery, Chiron was close to aphelion, whereas the observations showing a coma were done closer to perihelion, perhaps explaining why no cometary behavior had been seen earlier. The fact that Chiron is still active probably means it has not been in its current orbit very long.<ref name="Perihelion" />

Chiron is officially designated as both a comet—95P/Chiron—and a minor planet,<ref name="dualstatus" /><ref name="Fornasier-2013" /> an indication of the sometimes fuzzy dividing line between the two classes of object. The term proto-comet has also been used. Being about 220&nbsp;km in diameter, it is unusually large for a [[comet nucleus]]. Chiron was the first member of a new family of [[Chiron-type comet]]s (CTC) with ([[Tisserand's parameter|T<sub>Jupiter</sub>]] > 3; [[Semi-major axis|a]] > a<sub>Jupiter</sub>).<ref name="jpldata" /> Other CTCs include: [[39P/Oterma]], [[165P/LINEAR]], [[166P/NEAT]], and [[167P/CINEOS]]. There are also non-centaur asteroids that are simultaneously classified as comets, such as [[4015 Wilson–Harrington]], [[7968 Elst–Pizarro]], and [[118401 LINEAR]].<ref name="dualstatus" />

Since the discovery of Chiron, other centaurs have been discovered, and nearly all are currently classified as minor planets, but are being observed for possible cometary behavior. [[60558 Echeclus]] has displayed a cometary coma and now also has the cometary designation 174P/Echeclus. After passing perihelion in early 2008, [[52872 Okyrhoe]] significantly brightened.<ref name="cometary" />