In June 2013, a stellar occultation revealed for the first time ever the presence of two dense and narrow rings around a small object of the solar system, the Centaur (10199) Chariklo (Braga-Ribas et al., Nature 508, 72, 2014). This body follows an eccentric orbit between Saturn and Uranus, with perihelion and aphelion distances of 13.1 and 18.5 AU. Due to Uranus perturbations, its orbit is unstable on the very short time scale of ~10 Myr (Horner at al. MNRAS 354, 798, 2004). The two rings (C1R and C2R, respectively) have orbital radii aC1R= 390.6±3.3 km and aC2R= 404.8±3.3 km, and typical widths WC1R ~6.5 km and WC2R ~2 km, optical depths τC1R ~ 0.4 and τC1R ~ 0.06, with a gap of ~9 km between the two. Chariklo's radius, RC~ 120 km (Duffard et al. AA 568, A79, 2014 Fornasier et al. AA 518, L11, 2014), implies that the ring system lies at 3.3-3.4 RC, farther away than the classical Roche limit of 2.4 RC that would be obtained for spherical ring particles with the same density as Chariklo.To better understand Chariklo's surroundings, and thus the origin of the rings, direct imaging of Chariklo has been performed using HST and VLT, with respectively 3 visits and 2 runs performed between April and August 2015. The HST images were obtained with the WFC3/UVIS camera with filters F300X (250-350 nm), F475X (400-650 nm) and F350LP (300-1000 nm), and typical PSF size of 30 milli-arcsec (mas), corresponding to about 300~km at Chariklo. Conversely, the SPHERE high contrast instrument at ESO VLT provided images in the near IR (Y, J and H bands), with typical expected PSF sizes of 30-40 mas (300-400~km at Chariklo). The main goals of those observations were: (1) obtain direct images of the rings, confirming their geometry and their orientation, (2) derive multi-wavelength photometry, thus constraining their composition (concerning in particular the presence of water ice), (3) perform a deep search of small satellites (down to a few km in diameter), (4) faint dusty rings around Chariklo (down to about τ ~10-5-10-6), and (5) search possible cometary jets or coma, akin to what is observed around another Centaur, Chiron (Ortiz et al. AA 576, A8, 2015). Premiminary results obtained from those observations will be presented.
AAS/Division for Planetary Sciences Meeting Abstracts #47
- Pub Date:
- November 2015