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

Thermal inertias Gamma 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 Gamma(B)=5(-2)(+18) J m(-2) K-1 s(-1/2) and Gamma(C)=6(-4)(+12) 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.