Adhesion and collisional release of particles in dense planetary rings

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• 作者：Anna Bodrova^a ; ^b ; ^{bodrova@polly.phys.msu.ru} ; Jü ; rgen Schmidt^a ; Frank Spahn^a ; Nikolay Brilliantov^c
• 关键词：Planetary rings ; Saturn ; Rings ; Collisional physics
• 刊名：Icarus
• 出版年：2012
• 期刊代码：90_00191035
• 类别：ph
• 出版时间：March, 2012
• 卷：218
• 期：1
• 页码：60-68
• 文件大小：620 K

摘要

We propose a simple theoretical model for aggregative and fragmentative collisions in Saturn鈥檚 dense rings. In this model the ring matter consists of a bimodal size distribution: large (meter sized) boulders and a population of smaller particles (tens of centimeters down to dust). The small particles can adhesively stick to the boulders and can be released as debris in binary collisions of their carriers. To quantify the adhesion force we use the JKR theory (Johnson, K., Kendall, K., Roberts, A. [1971]. Proc. R. Soc. Lond. A 324, 301-313). The rates of release and adsorption of particles are calculated, depending on material parameters, sizes, and plausible velocity dispersions of carriers and debris particles. In steady state we obtain an expression for the amount of free debris relative to the fraction still attached to the carriers. In terms of this conceptually simple model a paucity of subcentimeter particles in Saturn鈥檚 rings (French, R.G., Nicholson, P.D. [2000]. Icarus 145, 502-523; Marouf, E. et al. [2008]. Abstracts for 鈥淪aturn after Cassini-Huygens鈥?Symposium, Imperial College London, UK, July 28 to August 1, p. 113) can be understood as a consequence of the increasing strength of adhesion (relative to inertial forces) for decreasing particle size. In this case particles smaller than a certain critical radius remain tightly attached to the surfaces of larger boulders, even when the boulders collide at their typical speed. Furthermore, we find that already a mildly increased velocity dispersion of the carrier-particles may significantly enhance the fraction of free debris particles, in this way increasing the optical depth of the system.