With each close flyby of another of Saturn's icy moons, I'm struck by some similarities.
Each moon we've looked at closely (Iapetus, Rhea, Enceladus, et. al.) has shown features common to Jovian icy moons, plus some unique features of their own. That's to be expected, they're all unique worlds.
But we see a pattern of global stress fracturing on *every single one* of the icy moons that we've looked at thus far. Stress fracturing that seems non-common to the ways in which we understand fracturing on icy moons.
I'm struck by the images of Enceladus that have just come in -- that world looks like its surfacing is older but very similar to that of Europa. But there are cracks, both straight and arcuate, that do not correlate with the surface formation patterns. They seem to be stress fractures caused by a different process than the actual surfacing processes.
You see similar cracks and, well, distortion features on the other icy moons, including a hemisphere-girdling ridge that makes Iapetus look like a clay ball that someone tried to twist into two halves.
These distortion features could have different causes in each case, I suppose. But they look suspiciously like gravitationally-induced distortions to my (admittedly untrained) eye.
And, of course, you do have to evaluate the condition of the surfaces of the icy moons in the context of the presence of the rings themselves -- possibly evidence of entire worlds that were broken into particles no bigger than grains of sand. Possibly caused by impact processes, or perhaps gravitational processes. Or both.
You could explain all of this by unique gravitational resonances in the Saturn system, I suppose... though it seems odd to me that you don't see this kind of commonality of gravitationally-induced distortion features on Jupiter's icy moons. But when I look at the distortion features stratigraphically, it *really* seems to me that they overly *all* of the surfaces, from the oldest to the youngest, that we see on the icy moons.
So, we *seem* to have a stratigraphic process in which the Saturnian icy moons developed surfaces in ways similar to those we've seen in the Jovian moons. And then we see each of these moons displaying gravitational distortion features overlying surfaces of nearly all ages.
This would speak to some type of catastrophe (gravitational or otherwise) occurring within the Saturn system after its icy moons had developed their surfaces to pretty much what we see today.
So, I guess the question is -- what the heck happened at Saturn???
And when?
-the other Doug