[X] My Assistant

[Rob Pinnegar]

On quite a few occasions I've seen Mimas' big crater Herschel described as being the result of an impact that came close to breaking Mimas apart. Today I was looking at an image of Mimas and what really struck me is the fact that Herschel sits pretty close to the middle of the leading hemisphere (hope I've got that right) and it's also just about right on the equator.

This is a long shot, but could Herschel be the result of a collision between Mimas, and a Mimas co-orbital that wasn't able to stay in the Lagrange point because of perturbations from Enceladus and the other large moons? The fact that Herschel is a bit off-centre in the leading hemisphere isn't a _huge_ problem, since Lagrangian orbits can be a bit elliptical.

What I'm thinking is that, if the co-orbital was big enough, this could provide a larger crater than what would normally be the limit for shattering the moon, due to the relatively low impact velocity.

Herschel is pretty deep, and has a pronounced central peak, which speaks to a violent origin. And Mimas is so small that it would have had difficulty grabbing a Lagrangian moon in the first place. So this hypothesis probably doesn't have a whole lot of merit. Still, I was curious to find out what people think -- and whether this mechanism could explain features on any other Solar System moons. Would a very-low-velocity impact give an identifiable crater configuration?

I'm tempted to speculate about Mare Orientale and solar perturbations, but have probably gone far enough out on a limb for one day.

[ljk4-1]

Unravelling Temporal Variability in Saturn's Spiral Density Waves: Results and Predictions

http://arxiv.org/abs/astro-ph/0609242