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]

OK -- I understand your conclusion, here. But I still want to hear your theory for how Iapetus got a dark, reddish natural surface, and from where the bright ices that are covering this dark surface came. If insolation can "burn off" the snow from sun-facing slopes, over billions of years, shouldn't it have burned off ALL of the snow?

Iapetus has no atmosphere, so we're not talking about a hydrocycle, here. If what everyone has been saying is true and it's stone-cold dead, it hasn't vented icy plumes for billions of years. So why hasn't all of the snow been burned off, the vapor sputtered into space?

And, to reiterate -- how did this entire moon get surfaced with a dark reddish material that's different in composition from any of the other icy moons, and yet seems similar in composition to Titan's atmosphere?

Before I can accept the concept that the dark material is the natural surface and the icy snow lies on top of it, I need to hear a mechanism postulated that accounts for this dark surfacing. And just saying "Well, it's probably a KBO, that explains it" doesn't explain a thing for me... show me where KBOs follow a pattern of having dark, reddish surfaces and explain how they *all* got surfaced that way, and maybe I'll start to consider it. But until then, Occam's Razor tells me that any airless icy body that was born anywhere near Saturn ought to have a bright icy surface, and that any significant darkening must be an overlay on top of that icy surface.

-the other Doug

[ugordan]

And, to reiterate -- how did this entire moon get surfaced with a dark reddish material that's different in composition from any of the other icy moons, and yet seems similar in composition to Titan's atmosphere?

I haven't seen this one mentioned before. Is there any reference to this? All I've seen is comparisons to Phoebe's spectra and Hyperion.
Some related links:
http://saturn.jpl.nasa.gov/multimedia/prod...ARM_verH_FC.pdf
http://saturn.jpl.nasa.gov/multimedia/prod...HARM_050125.pdf

The first CHARM presentation has an interesting bit:

The IR spectra show that Phoebe dark material is similar to Iapetus dark material, but the visual spectra show that Hyperion and Iapetus are more similar.

If it was just white holes filled with black material melting the ice, one has to explain the black basin walls, which I find hard to do

I'm seeing lots of very small craters that have dark bottoms, but I guess everyone sees things differently. I wouldn't say the dark material is doing any melting here, far too cold for that, but the ice can slowly sublimate away from the regolith, at least from the depth through which sun can penetrate into.