Iapetus - Black on white or white on black? Options

[SFJCody]

Seems to be a lot of dispute on this subject... I think it's ice from the interior, but what does everyone else think?

Edit:

This world seems very complex so the question could perhaps be phrased as 'which of these options is most responsible for the Iapetan dichotomy?'

[dvandorn]

After seeing some of the contrast-enhanced images from the trailing hemisphere, I have to say that my view has changed slightly. I still firmly believe that the dark surface on the leading edge is a mantling on top of a brighter ice substrate, but there is good evidence now that where this dark material has mantled the surface along the edges of the leading hemisphere, there has been deposition of bright ices on top of it. In places.

What is so odd to me is that neither hemisphere shows much in the way of cratering that exhumes a different-albedo substrate. There are occasional bright-rimmed craters on the leading hemisphere, but almost no dark-halo craters on the trailing one. And the bright-rimmed craters are just that -- bright-rimmed. There is little to no evidence of bright ejecta around them.

I'm having a hard time believing that the impact rate is so small that there have simply been few to no impacts of any size since the materials we see were emplaced on Iapetus' surface. But at the same time, I have a similarly hard time believing that the emplacement of these materials is anything but ancient -- particularly since some of the flow patterns hint at *aeolian* deposition/deflation, which is awfully difficult to explain on a currently airless body.

So we are left with a paradox.

-the other Doug