  Aims. To investigate the mid-infrared (MIR) characteristics of Saturn's
rings. Methods. We collected and analyzed MIR high spatial resolution images of
Saturn's rings obtained in January 2008 and April 2005 with COMICS mounted on
Subaru Telescope, and investigated the spatial variation in the surface
brightness of the rings in multiple bands in the MIR. We also composed the
spectral energy distributions (SEDs) of the C, B, and A rings and the Cassini
Division, and estimated the temperatures of the rings from the SEDs assuming
the optical depths. Results. We find that the C ring and the Cassini Division
were warmer than the B and A rings in 2008, which could be accounted for by
their lower albedos, lower optical depths, and smaller self-shadowing effect.
We also find that the C ring and the Cassini Division were considerably
brighter than the B and A rings in the MIR in 2008 and the radial contrast of
the ring brightness is the inverse of that in 2005, which is interpreted as a
result of a seasonal effect with changing elevations of the sun and observer
above the ring plane.
