Imaging Saturn's rings with CAMIRAS: thermal inertia of B and C rings

Abstract

Thermal inertias Γ of Saturn's B and C ring particles have been derived from infrared observations using the CAMIRAS camera mounted on the Canada-France-Hawaii Telescope. They are respectively Γ_B=5⁺¹⁸_-2 {J m^-2 K^-1 s^-1/2} and Γ_C=6⁺¹²_-4 {J m^-2 K^-1 s^-1/2}. Such low values might be characteristic of a frosty and porous regolith fractured by cracks or of very porous particle aggregates. Particles have to be slowly spinning to explain the observed ring temperatures. A large azimuthal asymmetry with an amplitude about 1 K is detected on the West ansa of the B ring. It cannot be explained by a model that considers the ring as a slab of low thermal inertia rapidly warming up to the sunlight after its eclipse into the planetary shadow.