Victoria's Innards, Your last chance to speculate before we really see it |
Victoria's Innards, Your last chance to speculate before we really see it |
Sep 27 2006, 05:40 AM
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#46
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Member Group: Members Posts: 160 Joined: 4-July 05 From: Huntington Beach, CA, USA Member No.: 429 |
Has anyone considered the possibility that Victoria could be a caldera rather than a crater? Seems a bit wild I'm sure but this is a very unusual crater. It is highly eroded yet still has a distinct bowl shape. I find it so bizarre. I wish some genius would explain its morphology. The degree of erosion is incredible given the fact the form of the crater is well preserved. It must be very very soft stuff those blueberries are in, evaporite or whatever because the wimpy Martian wind can blow it away. It's easy to underestimate the size of Victoria by looking at the images taken by Opportunity so far. It's much bigger than it seems, but not much deeper. Look at the photographs from space - there are wide ledges along the rim. They look very steep in the MER images. I believe the diameter to depth ratio for rocky meteorites is 10:1. If Victoria is 800m wide, its initial depth must have been 80m, and now it's 40 or so. That's a lot of stuff! The bigger the crater, the more is the ratio of the volume displaced by the impact to the volume displaced by erosion in the given time. |
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Sep 27 2006, 07:44 AM
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#47
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Senior Member Group: Members Posts: 3009 Joined: 30-October 04 Member No.: 105 |
>explain its morphology
It's a crater. --Bill -------------------- |
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Sep 28 2006, 01:02 AM
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#48
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Member Group: Members Posts: 240 Joined: 18-July 06 Member No.: 981 |
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Sep 28 2006, 11:51 AM
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#49
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Member Group: Members Posts: 100 Joined: 20-May 06 Member No.: 780 |
Bill, thanks for posting the Meteor crater formation. That looks like a good starting point for Victoria.
I know we don't have a realistic estimate for Victoria's age yet (other than "old"), but I want to keep in mind that Mars' atmosphere might well have been more substantial, enough to have more effect on wind-driven erosion of the cliff walls. Do we have any useful estimates of Martian atmospheric density over the life of the planet? |
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Sep 28 2006, 03:14 PM
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#50
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Senior Member Group: Members Posts: 1887 Joined: 20-November 04 From: Iowa Member No.: 110 |
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Sep 28 2006, 09:07 PM
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#51
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Senior Member Group: Members Posts: 3009 Joined: 30-October 04 Member No.: 105 |
Alan, I've not got this one figured out either. The lower, arcuate part looks like a failure surface along impact-induced fractures. Above that it looks jumbled like ejecta. Then above that is a well-defined horizontal layer, with sand above that. Very complex.
--Bill -------------------- |
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Sep 29 2006, 01:39 PM
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#52
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Member Group: Members Posts: 242 Joined: 17-February 04 From: Ohio, USA Member No.: 34 |
Boundary between original surface and ejacta blanket? I see some blocks that appear to have layering at an angle though it is difficult to tell with the jpeg artifacts. Material below line reminds me of top, evaporite, layer in Endurance I agree; this is some complex stratigraphy. Alan has picked the lower boundary of what might be called a 'megabreccia'. And certainly there is a fine-grained lighter colored layer at the very top. It looks as if there is another layer of jumbled rocks between these two. In a couple of places the layer appears to have draped over the boulders of the 'megabreccia'. The layer immediatly below alan's yellow line is also highly fractured. But the fragments here are more similar in size than the jumble of boulders and debris in the 'megabreccia' above the yellow line. I'd be very reluctant to try to make any correlations with Endurance at this point. That's my take anyway. This is going to take some time and more images to figure out. |
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Sep 29 2006, 04:26 PM
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#53
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Member Group: Members Posts: 252 Joined: 27-April 05 Member No.: 365 |
Perhaps the layer just below the fine surface coating is lava flows that 'draped' over the Megabreccia, then got soaked in water. The thin top layer is probably what has been quietly accumulating since things quieted down on the planet.
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