 Diagram of Chariklo and its rings as seen during astellar occultation on 3 June 2013. This diagram was constructed by plotting the respective time and location of theobservatories that recorded the occultation. | |
| Discovery[1] | |
|---|---|
| Discovered by | Spacewatch[a] |
| Discovery site | Kitt Peak Obs. |
| Discovery date | 15 February 1997 |
| Designations | |
| (10199) Chariklo | |
| Pronunciation | /ˈkærəkloʊ/[2] |
Named after | ΧαρικλώKhariklō (Ancient Greek nymph)[1] |
| 1997 CU26 | |
| centaur[3] · distant[1] | |
| Adjectives | Charikloan, Charikloian/kærəˈkloʊ(i)ən/ |
| Symbol | .svg) [4] |
| Orbital characteristics[3] | |
| Epoch 5 May 2025 (JD 2460800.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 36+ yr |
| Earliestprecovery date | 5 November 1988 |
| Aphelion | 18.420AU |
| Perihelion | 13.077 AU |
| 15.748 AU | |
| Eccentricity | 0.1696 |
| 62.50yr (22,827 days) | |
| 123.744° | |
| 0° 0m 56.774s / day | |
| Inclination | 23.425° |
| 300.470° | |
| 241.323° | |
| Saturn MOID | 4.710 AU[1] |
| Uranus MOID | 3.186 AU[1] |
| Physical characteristics | |
| Dimensions | (287.6+2.8 −3.0) × (270.4+2.8 −5.6) × (198.2+10.8 −5.4) km[7]: 11 |
| 249.6+6.0 −4.6 km[7]: 11 | |
| Mass | (5.9–6.9)×1018 kg[b] |
Meandensity | 0.73–0.85 g/cm3[7]: 9 |
| 7.004±0.036 h[8][7]: 8 | |
North poleright ascension | 151.03°±0.14° (C1R ring)[7]: 11 |
North poledeclination | +41.81°±0.07° (C1R ring)[7]: 11 |
| 0.037±0.001[9]: 14 [7]: 10 | |
| ~19[1][11] | |
| 6.8–7.3[c] | |
10199 Chariklo/ˈkærəkloʊ/ is a ringedasteroid orcentaur in the outerSolar System. It is the largest known centaur, with a diameter of about 250 km (160 mi). It orbits the Sun betweenSaturn andUranus with anorbital period of 62.5 years. It was discovered on 15 February 1997 by theUniversity of Arizona'sSpacewatch project atKitt Peak National Observatory. Chariklo has a dark, reddish surface composed of water ice,silicate minerals,amorphous carbon, and various complexorganic compounds (also known astholins).
Chariklo'sring system consists of two narrow rings of icy particles in orbit around the object. Therings of Chariklo were discovered in 2013, when astronomers observed Charikloocculting or passing in front of a star. Chariklo was the firstminor planet discovered to have rings, and as of 2025[update], it is one of thefour minor planets known to have rings (the three others being2060 Chiron,Haumea, andQuaoar). It is unknown what keeps Chariklo's rings stable, as it has been predicted that they should decay within a few million years.[12] Astronomers have hypothesized that Chariklo's rings might be maintained by the gravitational influence of yet-undiscoveredshepherd moons orbiting Chariklo.[13] The origin of Chariklo's rings is uncertain, with various possible explanations including ejection of surface material viaoutgassing ortidal disruption of a moon around Chariklo.[13]: 1
Chariklo was discovered on 15 February 1997 by theUniversity of Arizona'sSpacewatch project atKitt Peak National Observatory.[1]James V. Scotti made the discovery observations using the Spacewatch 0.9-meter telescope,[14][15] althoughNASA and theMinor Planet Center (MPC) do not mention him as the official discoverer.[3][1][16] Other observatories fromCanada,Czech Republic, andChina continued observing Chariklo until the discovery was announced by the MPC on 24 February 1997. The MPC gave theprovisional designation1997 CU26 to the object.[14] Chariklo was the seventhcentaur discovered.[17]: 457 [d]
Within a year after Chariklo was discovered, astronomers observed the object in detail to characterize its properties, including itscolor,[18] size,[19] and surface composition.[20] On 2 March 1999, the MPC gave Chariklo itsminor planet catalog number of 10199.[21]: 89 Chariklo was officially named on 28 September 1999.[22]: 365
This minor planet is named after thenymphChariclo (Χαρικλώ), the wife ofChiron inGreek mythology.[1] Chariclo has sometimes been characterized as a sea nymph, female centaur, or the mother of the blind prophetTiresias.[1] An astrological symbol for Chariklo,
, was devised in the late 1990s by German astrologer Robert von Heeren.[4] Chariklo's symbol was derived from the astrological symbol used for the centaur2060 Chiron,.svg)
, where the letter C replaces the letter K.[4]
Chariklo orbits the Sun betweenSaturn andUranus[23]: 1 with an average orbital distance of 15.7 astronomical units (AU) and anorbital period of 62.5 years.[3] It follows aninclined andelliptical orbit that brings it within13.1 AU from the Sun atperihelion to as far as18.4 AU ataphelion.[3] Chariklo is close to, but not in a 4:3orbital resonance with Uranus; its mean orbital distance lies within0.09 AU from the resonance.[24]: 802
Chariklo is classified as acentaur, a type ofsmall Solar System body generally[e] defined as orbiting between Jupiter and Neptune.[25]: 1 [23]: 1 Centaurs, which share characteristics of bothasteroids andcomets,[26] are thought to have originated from theKuiper belt and thescattered disc beyond Neptune.[23]: 1 The centaurs are stronglyinfluenced by the gravity of the giant planets, which leads tochaotic or unpredictable changes in their orbits.[25]: 1–2 Such changes can lead to centaurs escaping their orbital region by either getting ejected from the Solar System,impacting a planet, or becoming ashort-period comet whose orbit enters the inner Solar System.[24]: 1
Compared to other centaurs, Chariklo's orbit is relatively more stable[23]: 1 with a 50% chance of escaping the centaur region 7[27]: 4772 or 10.3[24]: 802 million years in the future.[f] Chariklo's orbital evolution is primarily influenced by Uranus; simulations predict that Chariklo will frequently make close approaches to Uranus during the next 100 million years.[25]: 1, 3 However, Chariklo's less frequent future encounters with Jupiter and Saturn will have greater effects on its orbit and can potentially disrupt Chariklo's ring system.[25]: 4, 6
Simulations show that there is a 99% chance that Chariklo was implanted in the centaur region sometime in the past 20 million years.[23]: 5 There is a 50% chance that Chariklo could have been implanted as recently as 9.38 million years ago.[24]: 802 [23]: 2 A 2016 study suggested that Jupiter and Saturn were responsible for transferring Chariklo to the centaur region,[25]: 6 whereas a 2017 study suggested Neptune was more likely responsible.[23]: 6
Chariklo's brightness orapparent magnitude lies between 17 and 19, depending on its distance from Earth.[29] Chariklo appeared brightest from Earth in 2003 when it was simultaneously at perihelion andopposition.[30] Independent of distance, Chariklo's intrinsic brightness orabsolute magnitude (H) changes over time due to the changing viewing angle of Chariklo's rings as seen from Earth.[9]: 11 During the late 1990s and early 2000s, Chariklo appeared brighter (H=6.8) because more of its rings' surface area was visible from Earth.[9]: 11 On the other hand, during 2008, Chariklo appeared fainter (H=7.3) because its rings were seen edge-on (minimum visible surface area) from Earth.[9]: 11
Chariklo and its rings are too small and too far away to be resolved by current telescopes.[28][7]: 2 Chariklo's rings span anangular diameter of 80milliarcseconds in the sky, close to thediffraction limit of some of the highest-resolution telescopes like theHubble Space Telescope.[7]: 2 These telescopes have not been able to detect Chariklo's rings through direct imaging.[31][7]: 2 Chariklo's rings may be imageable in the future with even larger telescopes such as theExtremely Large Telescope.[32]: 29
During 2013 to 2022, Chariklo was passing in front of theGalactic Center in the sky.[32]: 29 Because the Galactic Center is densely packed with stars, this meant Chariklo wouldoccult or pass in front of multiple stars.[32]: 29 Stellar occultations allow for accurate measurements of a Solar System object's position, size, shape, and surrounding features (i.e. moons and rings) at kilometre-scale resolutions.[7]: 2 Chariklo was first observed via stellar occultation on 3 June 2013, which resulted in the discovery of Chariklo's rings.[7]: 1 Between 2014 and 2022, about twenty observing campaigns were organized by astronomers to observe predicted occultations by Chariklo.[32]: 29 These campaigns involved international collaboration between professional andamateur astronomers.[7]: 2 [32]: 29
Multiple years of occultation observations show that Chariklo is aflattened or elongated body[9]: 22 with dimensions of approximately 288 km × 270 km × 198 km (179 mi × 168 mi × 123 mi).[7] Thevolume-equivalent mean diameter of Chariklo is about 250 km (160 mi).[7]: 11 This makes Chariklo the largest known centaur.[7]: 1
Chariklo's shape is consistent with atriaxial ellipsoid,[7]: 1 although slight differences between occultation measurements hint attopographic variation or irregularities in its shape.[7]: 9 [9]: 19 Chariklo's topographic deviations from an ellipsoid may be as low as −5.52 km (−3.43 mi) to as high as 7.78 km (4.83 mi) (standard deviation 4.11 km or 2.55 mi).[7]: 9 The amount of topographic variation seen in Chariklo is similar to those seen in Saturn's small icy moonsPhoebe andHyperion.[9]: 20 Simulations of Chariklo's rings predict that ring particles can fall and accumulate on Chariklo's equator to form anequatorial ridge, similar to that on Saturn's moonIapetus.[33]: 149
Chariklo's dimensions and rotation period suggest it is not inhydrostatic equilibrium.[7]: 9 Although Chariklo's mass and density have not been measured due to its lack of known moons,[9]: 7 a range of possible masses and densities can be estimated by assuming Chariklo's rings are in a 1:3 spin-orbit resonance with Chariklo's rotation, similar to other ringed minor planets.[7]: 9 This gives a density range of0.73–0.85 g/cm3,[7]: 9 which is expected for an icy body.[9]: 22 This density range corresponds to a mass range of(5.9–6.9)×1018 kg for Chariklo.[b] If Chariklo was in hydrostatic equilibrium, it should have a density between0.8–1.25 g/cm3 and a mass between(6–8)×1018 kg, depending on its dimensions.[9]: 22
Chariklo has asynodic rotation period of 7.004 hours, with an uncertainty of 0.036 hours (2.2 minutes).[8][7]: 8 Due to Chariklo's elongated shape, its apparent brightness from Earth changes as it rotates, although the amount of change depends on the viewing angle of Chariklo as seen from Earth.[8]: 3 Chariklo's brightness can vary as much as 0.13magnitudes when looking at its equator, whereas its brightness changes may be undetectable when looking at its poles.[7]: 10 [8]: 1 Astronomers first attempted to measure Chariklo's rotation period in 1997, but were unable to detect any brightness changes since Chariklo was viewed pole-on from Earth at the time.[7]: 10 It was not until 2013 that astronomers were able to measure Chariklo's rotation period.[8]: 2
If Chariklo's rotation is aligned with its rings, then its rotational north pole would point in the direction (RA,Dec) = (151.0°, +41.8°).[7] This translates toecliptic coordinates (λ,β) = (137.6°, +27.9°),[35] which means Chariklo'saxial tilt is 62.1° with respect to the ecliptic.[g]
_(01GQJ89HXD39F20PSXS2KKKREB).png)
The surface of Chariklo is dark and reddish with a lowgeometric albedo of 3.7%.[9]: 14 [7]: 10 Invisible light, thereflectancespectrum of Chariklo appears featureless, lacking clearabsorption features associated with compounds on its surface.[36]: 1 These characteristics led astronomers to classify Chariklo as aD-type asteroid.[18][37]: 232 Astronomers have also classified Chariklo as part of theBR class of centaurs and trans-Neptunian objects, whose colors are considered intermediate between "spectrally neutral" (gray) and "red".[38]: 1292 [10]: 181, 183
Innear-infraredwavelengths, Chariklo's spectrum shows several absorption features that suggest its surface is composed of water ice,silicate minerals,amorphous carbon, and various complexorganic compounds (also known astholins).[39][28]Spectroscopic observations over different years have shown varying levels of water ice in Chariklo's near-infrared spectrum, which astronomers attribute to the changing viewing angle of Chariklo's water ice-rich rings.[39] Near-infrared spectroscopy by theJames Webb Space Telescope in 2022 has shown that Chariklo's surface containswater ice in crystalline form,[28] contrary to initial beliefs that all water ice was concentrated in Chariklo's rings.[39] Crystalline water ice is expected to be short-lived in space due to irradiation by high-energy particles, so astronomers hypothesize that Chariklo experiences continuous micro-impacts that either expose pristine material or trigger crystallization processes.[28]
Chariklo does not appear to exbibit cometary activity, unlike the other ringed centaur2060 Chiron.[8]: 4 [23]: 2 A 2014 analysis of Chariklo's appearance in high-resolution telescope images from 2007–2013 found no evidence of a dustcoma surrounding Chariklo, placing an upper limit dust production rate of2.5 kg/s.[8]: 4 Likewise, observations by theVery Large Telescope and Hubble Space Telescope in 2015 found no signs of cometary jets or dust beyond 300 km (190 mi) from Chariklo.[31][7]: 2 Chariklo is likely too cold and too far away from the Sun to exhibit cometary activity today.[40]: 12 However, the unstable nature of Chariklo's orbit suggests it is possible that it could have orbited closer to the Sun, meaning Chariklo could have been warmer and active in the past.[23]: 7 [40]: 12
_(01GQJ8KESB02G5QGRBZ64AFFAF).png)
A stellaroccultation in 2013[12][41] revealed that Chariklo has tworings with radii 386 and 400 km and widths of about 6.9 km and 0.12 km respectively.[7] The rings are approximately 14 km apart.[7] This makes Chariklo the second smallest known object to have rings after its fellow centaur Chiron. These rings are consistent with an edge-on orientation in 2008, which can explain Chariklo's dimming before 2008 and brightening since. Nonetheless, the elongated shape of Chariklo explains most of the brightness variability resulting in darker rings than previously determined.[9] Furthermore, the rings can explain the gradual disappearance of the water-ice features in Chariklo's spectrum before 2008 and their reappearance thereafter if the water ice is in Chariklo's rings.[12][26][42]
The existence of a ring system around a minor planet was unexpected because it had been thought that rings could only be stable around much more massive bodies.[43] Ring systems around minor bodies had not previously been discovered despite the search for them through direct imaging and stellar occultation techniques.[12] Chariklo's rings should disperse over a period of at most a few million years, so either they are very young, or they are actively contained byshepherd moons with a mass comparable to that of the rings.[13][12][26][42] However, other research suggests that Chariklo's elongated shape combined with its fast rotation can clear material in an equatorial disk throughLindblad resonances and explain the survival and location of the rings, a mechanism valid also for the ring ofHaumea.[33]
The team nicknamed the ringsOiapoque (the inner, more substantial ring) andChuí (the outer ring), after the two rivers that form the northern and southern coastal borders of Brazil. A request for formal names will be submitted to theIAU at a later date.[26]
It has been confirmed that Chiron may havea similar pair of rings.[44]
| Name | Nickname | Orbital radius (km) | Width (km) | Eccentricity | Normaloptical depth | Surface density (g/cm2)[12]: 73 | Mass-equivalent diameter (km)[12]: 73 | Pole direction (RA) | Pole direction (Dec) | Radial separation (km) |
|---|---|---|---|---|---|---|---|---|---|---|
| C1R | Oiapoque | 385.9±0.4 | 4.8 to 9.1 | 0.005 to 0.022 | 0.4 (average)[h] | 30–100 | ~2 | 151.03°±0.14° | +41.81°±0.07° | 13.9+5.2 −3.4 |
| C2R | Chuí | 399.8±0.6 | 0.1 to 1 | <0.017 | >0.1 | ? | ~1 | 150.91°±0.22° | +41.60°±0.12° |
Camilla is a mission concept published in June 2018 that would launch a robotic probe to perform a singleflyby of Chariklo and drop off a 100 kg (220 lb) impactor made oftungsten to excavate a crater approximately 10 m (33 ft) deep for remote compositional analysis during the flyby.[45] The mission would be designed to fit under the cost cap of NASA'sNew Frontiers program, although it has not been formally proposed to compete for funding. The spacecraft would be launched in September 2026, using one gravity assist from Venus in February 2027 and Earth in December 2027 and 2029 to accelerate it out toward Jupiter.
| Planets | |
|---|---|
| Minor planets | |
| Moons |
|
| Related | |
