[X] My Assistant

[Guest_AlexBlackwell_*]

The June 1, 2006, issue of Nature has a new paper by Nimmo and Pappalardo entitled "Diapir-induced reorientation of Saturn's moon Enceladus" as well as an accompanying News and Views piece by Paul Hanlon. For the specific links, see the Editor's Summary.

[Rob Pinnegar]

Just as a sidenote: Looking up Saturn's orbital velocity about the Sun and Enceladus' orbital velocity about Saturn, it turns out that Enceladus is faster: about 12-13 km/s versus 9.6 for Saturn around the Sun. So Enceladus' angular velocity with respect to the Sun changes sign; it can move "backwards" as Saturn continues to move forwards.

This has got to cut down on the chances of Enceladus being "hit from behind" in a big way. When its velocity vector is parallel with Saturn's, could anything on a non-hyperbolic orbit around the Sun actually catch up with it? There's always the chance of being hit from the side by chance, of course, but statistically speaking the leading side really should take the brunt of the beating.

I always sort of felt that the idea of leading/trailing hemisphere asymmetry in crater counts was a bit of a pipe dream, due to the sheer number of craters involved, and "crater saturation" (though on Enceladus that may not be a huge issue). For outer moons like Iapetus where the moon's orbital velocity isn't a substantial fraction of Saturn's, this could be true... but in Enceladus' case one would think that it ought to be a noticeable effect (stressing here "ought to be")...