Possible ring material around centaur (2060) Chiron

Abstract

We propose that several short-duration events observed in past stellar occultations by Chiron were produced by ring material. Some similarities between these events and the characteristics of Chariklo's rings could indicate common mechanisms around centaurs. From a reanalysis of the stellar occultation data in the literature, we determined two possible orientations of the pole of Chiron's rings, with ecliptic coordinates λ = (352 ± 10)• , β = (37 ± 10)• . The mean radius of the rings is (324 ± 10) km. One can use the rotational lightcurve amplitude of Chiron at different epochs to distinguish between the two solutions for the pole. Both solutions imply a lower lightcurve amplitude in 2013 than in 1988, when the rotational lightcurve was first determined. We derived Chiron's rotational lightcurve in 2013 from observations at the 1.23 m CAHA telescope, and indeed its amplitude was smaller than in 1988. We also present a rotational lightcurve in 2000 from images taken at the CASLEO 2.15 m telescope that is consistent with our predictions. Out of the two poles, the λ = (144 ± 10)• , β = (24 ± 10)• solution provides a better match to a compilation of rotational lightcurve amplitudes from the literature and those presented here. We also show that using this preferred pole orientation, Chiron's long-term brightness variations are compatible with a simple model that incorporates the changing brightness of the rings while the tilt angle with respect to the Earth is changing with time. Also, the variability of the water ice band in Chiron's spectra as seen in the literature can be explained to a large degree by an icy ring system whose tilt angle changes with time and whose composition includes water ice, analogously to the case of Chariklo. We present several possible formation scenarios for the rings from qualitative points of view and speculate on why rings might be common in centaurs. We also speculate on whether the known bimodal color distribution of the centaurs could be due to centaurs with rings and centaurs without rings.

Size distribution of particles in Saturn’s rings from aggregation and fragmentation

“…Thus, our results provide another (quantitative) proof that the particle size distribution of Saturn's rings is not primordial. The same size distributions are expected for other collision-dominated rings, such as the rings of Uranus (42,43), Chariklo (44,45), and Chiron (46,47) and possibly around extrasolar objects (48)(49)(50).…”

On the Mass and Origin of Chariklo’s Rings

“…Recent reinterpretation of occultation data of the secondlargest Centaur, 2060 Chiron, as possible evidence of rings (Ortiz et al 2015;Ruprecht et al 2015) has further sharpened interest in ways to form rings around small bodies which have had close encounters with giant planets. Dynamical formation mechanisms proposed thus far for Centaur ring systems (see, for example, Braga-Ribas et al 2014;Duffard et al 2014; M. El Moutamid 2014, private communication) fall into two broad categories which we discuss in light of our findings in Section 2.…”

Photometry of Centaurs and trans-Neptunian objects: 2060 Chiron (1977 UB), 10199 Chariklo (1997 CU26), 38628 Huya (2000 EB173), 28978 Ixion (2001 KX76), and 90482 Orcus (2004 DW)

“…1, bottom panel, shows the detrended data (by fitting a linear function to the data and subtracting) from the top panel phased with the best-fit period, its amplitude is ∼0.1 mag. Its light-curve amplitude was found to be 0.088 mag in 1986 and 1988 (Bus et al 1989) and 0.044 mag in 1991 (Marcialis & Buratti 1993), but it was measured at 0.003±0.015 mag with data obtained in 2013 (Ortiz et al 2015). The raw data in Fig.…”

“…The rotational period of Chiron as determined by Bus et al (1989), Marcialis & Buratti (1993) or Sheppard et al (2008) & Jewitt 1990) and it may have a ring (Ortiz et al 2015;Ruprecht et al 2015). Because of this cometary activity, its absolute magnitude changes over time (Belskaya et al 2010).…”