Here is a paper http://adsabs.harvard.edu/abs/1978Icar...34..227G describing "The velocity dispersion in Saturn's rings".
It seems for the old papers, one would like to show the results in the first section.
This paper shows me how to deal with the collision term in the Boltzmann equation.
I derived the formulas in this marvel paper.
Elsarticle_Planet.pdf shows the main idea of derivation. I cannot find the pdf for Goldreich1978 just now. I hope this pdf can make my point. Based on this pdf, I wrote a draft to describe the planetesimal dynamics, which is rejected by ICARUS.
This pdf reminds me that how lonely I was when I started my astronomy study.