Unexpected discoveries of rings around small bodies in the solar system have been made since 2013. That year, dense rings were discovered around the Centaur Chariklo, then in 2017 around the dwarf planet Haumea, and more recently (2022) around the trans-Neptunian object Quaoar. Far from being limited to the four giant planets, rings are probably common around small objects in the outer solar system, as confirmed by the discovery of rings around Chiron announced here.
Chiron is a body approximately 200 km in diameter. It is a Centaur type object, originating from the Kuiper belt that extends beyond Neptune’s orbit. Due to perturbations caused by the giant planets, Chiron currently moves on a dynamically unstable orbit between Saturn and Uranus. In 2022, a stellar occultation by Chiron observed in Egypt and Israel revealed the presence of dense, confined material immersed in a diffuse halo. In 2023, more accurate observations, obtained in part with a 1.6-meter telescope at the Pico dos Dias Observatory in Brazil, revealed that this material is actually distributed in a complex disc surrounding Chiron.
Caption : Artist’s impression of Chiron’s rings, reconstructed from observations of a stellar occultation in 2023. The three rings appear as radial concentrations of matter, with the middle ring itself split into two very close rings. A halo of matter surrounds the two inner rings, and a diffuse outer ring surrounds the entire system.
Credits : Alexandre Crispim, UTFPR (Federal University of Technology - Paraná, Curitiba)
Structure of Chiron’s rings
Analysis of data from Pico dos Dias shows the presence of three dense rings around Chiron, with optical thicknesses varying between 5% and 30%. They are confined radially to a few kilometers and orbit at distances of 273 km, 325 km, and 438 km from the center of Chiron, respectively. These rings are themselves immersed in a halo of more diffuse material with an optical thickness of less than 2% that extends over several hundred kilometers. Finally, the entire system is bordered on the outside by a structure about 100 km wide with a low optical thickness of about 0.1%.
Chiron is similar in size and orbital parameters to another Centaur, Chariklo. The latter is surrounded by two rings, the main one of which is very dense, even opaque at certain points in its orbit. Since its discovery in 2013, this ring has remained unchanged in terms of both radius and radial structure. Chiron’s rings differ from those of Chariklo in their temporal variability. For example, a stellar occultation by Chiron observed in 2011 shows dense material near the 300 km orbital radius, but reveals no other dense structures or diffuse halo.
This difference could be explained by the fact that, unlike Chariklo, Chiron exhibits sporadic cometary activity during which material is ejected from the body. Chiron’s mass is large enough that this material does not escape into infinity, but instead remains around the body, quickly forming a disk, then narrow rings, with some of the material falling back onto the surface of the body.
The confinement of rings near certain specific radii could be due to spin-orbit resonances, implying a commensurability between the body’s rotation period and the revolution period of the ring particles. In this regard, it is interesting to note that the rings of Chariklo, Haumea, and Quaoar are all close to the 1/3 spin-orbit resonance with the central body, the latter completing three rotations while the particles in the rings complete one orbital revolution. A precise estimate of Chiron’s mass (which is not currently available) could provide the radii corresponding to the spin-orbit resonances, thereby confirming the dynamic link between the body and its rings.
The material observed around Chiron in 2013 could provide the first valuable example of a ring system in the process of formation. It could therefore provide insight into how other long-lasting ring systems may have formed around giant planets and small bodies.
References
The article is published under the title : “The Rings of (2060) Chiron : Evidence of an Evolving System” in The Astrophysical Journal Letters dated 20 octobre 2025.
Read the article.
Read the Press Release of National Observatory of Rio de Janeiro (Brazil).
This research has been partially funded by the “Roche” project of the French National Research Agency ANR-23-CE49-0012. It is the result of scientific activities carried out, among others, in France at the Paris Observatory - PSL at the Time and Space Laboratory (Paris Observatory - PSL / CNRS / Sorbonne University / University of Lille), at the “Laboratoire d’Instrumentation et de Recherche en Astrophysique (LIRA, Paris Observatory - PSL / CNRS / Sorbonne University, Paris Cité University), in Brazil (National Observatory of Rio de Janeiro, Federal University of Rio de Janeiro, Federal University of Technology in Curitiba) and in Spain (Institute of Astrophysics of Andalusia, Granada). These activities are part of the “Lucky Star” project, which includes professional and amateur collaborators from around the world.
Contacts
Bruno Sicardy
Professeur des universités SU, LTE
bruno.sicardy@observatoiredeparis.psl.eu
+33 (0) 1 40 51 23 34
Damya Souami
Chargée de recherche CNRS , LIRA
damya.souami@observatoiredeparis.psl.eu
+33 (0) 1 45 07 74 92
Josselin Desmars
Enseignant chercheur, IPSA et LTE
josselin.desmars@observatoiredeparis.psl.eu
+33 (0) 1 40 51 22 67
