Host: The Japanese Society for Planetary Sciences: Local Organizing Committee for 2006 Fall Meeting
The thermal infrared brightness of Saturn's rings isinvestigate based on the classical radiative transfer.In our model, the vertical heterogeneity of spin frequencies of ring particles and the heat transport due to vertical motion of particles are taken into account. We adopt a bimodal size distribution, in which rapidly spinning small particles with large orbital inclinations have surface temperatures closer to isothermal,relative to those for non-spinning large particles with small orbital inclinations. We find that our model reproduces surprisingly well the ring temperatures obtained by both Earth-based observations and by Cassini CIRS. For Earth-based observations, the large temperature increase with solar elevation angle observed in the A andB rings (called the tilt effect) can be reproduced contributed by all the effects mentioned above.Observations by Cassini CIRS show reduced temperatures at high solar phase angles, suggesting that at least some fraction of slowly spinning particles is necessary. Our model suggests that the contribution of slowly spinningparticles to the cross section is about 0.5, 0.8, and 0.5 for the A, B, and C rings, respectively.
