**DPS Pasadena Meeting 2000, 23-27 October 2000**

*Session 49. Rings Posters*

Displayed, 1:00pm, Monday - 1:00pm, Friday, Highlighted Tuesday and Thursday, 3:30-6:30pm, C101-C105, C211
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## [49.05] Gap Formation in Self-Gravitating Rings by an Embedded Moonlet

*K. Ohtsuki (U. Colorado), H. Tanaka (SWRI), S. Ida (Tokyo Inst. Tech.)*

We investigate gap formation in planetary rings due to
gravitational scattering by an embedded moonlet. Using
three-body orbital integrations including effects of
gravitational interactions and inelastic collisions, we
estimate the viscosity of self-gravitating planetary rings
with low optical depth. We find that the effect of
gravitational encounters between ring particles greatly
enhances the viscosity compared to non-gravitating cases,
unless the sum of the radii of the two interacting particles
is much larger than their mutual Hill radius. Using this
numerical value of the viscosity based on three-body orbital
integrations, minimum mass of a moonlet for gap formation is
obtained as a function of the surface number density and the
mass of ring particles as well as the distance from the
primary. We also carry out N-body simulations for a system
of ring particles and an embedded moonlet, where mutual
gravity and inelastic collisions are taken into account, and
find that the above estimate for the minimum mass of the
moonlet for gap formation agrees with the results of N-body
simulations.

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