Iapetus - Black on white or white on black? |
Iapetus - Black on white or white on black? |
Sep 14 2007, 07:40 AM
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#1
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Member Group: Members Posts: 813 Joined: 8-February 04 From: Arabia Terra Member No.: 12 |
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?' |
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Sep 14 2007, 04:33 PM
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#2
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Member Group: Members Posts: 114 Joined: 6-November 05 From: So. Maryland, USA Member No.: 544 |
I have to choose white on black on white - black endogenous, white both endo and exogenous.
Here's some of the things I see: Globally bright water ice with a cover of endogenous black gunk of varying thicknesses. Very thick on leading hemisphere, even big craters don't break through. Water ice brought to the surface and scattered about by impacts, some of them very large (Claude), which also contribute additional water ice. Gathers preferentially in impact-facing slopes, like Voyager Mts. White layer very thin in places, exposing dark ridges and bumps. Craters focus heat and start to remove bright material. Water ice removed from the leading hemisphere by some exogenous process and emplaced on the trailing hemisphere and poles through sublimation. Dark stuff spreads wherever it's exposed. Chunks of dark stuff hurled about by big impact(s), causes holes in thin bright ice layer where they fall. Crater rays can also remove white overlayer, leave dark lines. Black spreads by sublimating material around it. It looks to me like the Claude basin and its ejecta are comparatively recent; and are the controlling factor for a large swath of the moon north and west of the basin. We need to think about what happens when a large, icy body impacts a body with a layer of gunk overlying ice. It's interesting how a person's theories can affect what they see in these images, especially when there's the level of ambiguity we have at Iapetus. For example, I noted the little craters at the apex of certain parts of the equatorial ridge with great interest, especially considering that it looks as if portions of the ridge nearby seem to have moved and sunk. This doesn't look to me like a ridge emplaced by an infalling ring on a cold, dead world, but a ridge that was built and displaced by internal processes. But that's what I wanted it to be before I saw the images. ;-) |
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