Hello, first time poster (been lurking for a few days now, and Im learning a lot, thank you all very much)

I have a couple of questions about:



Larger image here

This image of Iapetus showing the ridge (ringe as mentioned earlier) has to be my favourite Cassini image to date - I wondered if there was any evidence of it extending further than the image shows? Any chance it could circle the whole equator?

I can see the ridge ends at the huge crater to the right of the image, which leads me to my second question - the crater covers a huge area but seems relatively shallow (I seem to vaguely remember reading the crater 'cliffs' were something like 12 miles high, please correct me if Im wrong) - would it be possible for a crater to form over such an area without being caused by an impact? (presumably some kind of geological event) Or do impact craters have a tendancy to 'infill' over time? (Ive seen another image of Iapetus showing a landslide inside a crater, so this seems likely, though that was on a much smaller scale)
Or am I wrong in assuming an impact crater will ALWAYS be significantly deeper at the center?

Your answers would greatly appreciated, thanks in advance.