Are the Arcs of Neptune Really Stable?
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**Session 65 -- SL-9 Impact, PLanets**
*Oral presentation, Tuesday, 10, 1995, 2:00pm - 3:30pm*

## [65.05] Are the Arcs of Neptune Really Stable?

*J. H\"anninen, C. Porco (LPL)*
The Voyager mission discovered a system of rings and ring arcs around Neptune.
It was later found that the arcs appear to be azimuthally and radially
confined by
resonant interactions with the nearby satellite, Galatea,
yielding a maximum spread
in ring particle semimajor axes of 0.6 km and a spread in forced
eccentricities large enough to explain the arc's 15 km radial widths
(Porco, 1991, *Science*
**253**
, 995).

We have modified an N-body simulation method (e.g. H\"anninen and Salo, 1992,
*Icarus*
**97**
, 228) to include Neptune's second and
fourth gravitational harmonics in order to be able to study the
effects of collisions and self-gravity on the stability of the ring arcs.
We have tested the
simulation method
and verified
the shepherding mechanism in the collisionless and non-self-gravitational
case. Preliminary simulation results with collisions over
$\frac{1}{2}$ a libration period indicate that
collisions among putative 10-m sized source bodies within the arcs are
indeed capable of arc disruption. However, whether or not collisions occur
over this time scale depends, among other factors, on the number
density of such bodies. We will explore the effects on arc stability
of varying simulation parameters, such as the sizes
and number density of the source bodies and the coefficient of restitution.
Also, we will examine the effect of Galatea's previously neglected nearby
vertical resonance on arc particle orbits.

**Tuesday
program listing**