Farewell Beacon..., The next cape beckons... |
Farewell Beacon..., The next cape beckons... |
Nov 27 2006, 06:31 AM
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#16
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Junior Member Group: Members Posts: 48 Joined: 26-August 05 Member No.: 475 |
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Nov 27 2006, 05:06 PM
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#17
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Member Group: Members Posts: 240 Joined: 18-July 06 Member No.: 981 |
Jeff7: Some of us think those dark streaks were formed by the removal of light colored dust rather than dark dust deposition. So, it may be a good place to go for Opportunity's solar panels. This streak debate seems to have legs and might become the next near-rim, far-rim brouhaha! Either way there could be wind blasting through there. |
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Nov 27 2006, 05:09 PM
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#18
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Member Group: Members Posts: 240 Joined: 18-July 06 Member No.: 981 |
As for the "dark" streaks this zoom of the high resolution colour Victoria crater TIF file suggests the dark material has moved come from / been blown from Victoria crater and overlayered lighter material. Victoria crater is below and to the right (about 5 o'clock) of these small craters. Yes, that's fascinating. Those craters could be candidates for a visit later on. I've often wondered about the petrified figure at the southeast rim. A lost sightseer perhaps? |
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Nov 27 2006, 07:34 PM
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#19
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Senior Member Group: Members Posts: 1229 Joined: 24-December 05 From: The blue one in between the yellow and red ones. Member No.: 618 |
Granted, CSM is higher stratigraphically, but not that much. This is true, of course, Tom, but why not grab the very top of the section when it's sitting there waiting for you to RAT it. And we have risk-free access to the exposed edge of the layer, as well as the top, without having to reach over the brink and risk a tumble down to the dunes. If the edge reveals laminae, and there is no discontinuity with the underlying layers, we have strong evidence that the beacon is in situ, and therefore points directly at an ancient (Noachian/Hesperian) formation of Victoria, followed by burial and recent exhumation. QUOTE The MIs displayed several large berries embedded in the rock and shaved by the RAT. They are pretty confident in their model of these concretions having formed in sediment saturated by ground water, or what is usually called the phreatic zone. On the trip south Opportunity climbed stratigraphically and observed no berries and micro-berries at the highest points, which is consistent with that model. But if the evaporite is in situ, then it indicates that ground water existed both below and above the berry-free strata. QUOTE The fact that they discovered large, embedded concretions in the rock here might suggest that these rocks came from the section that we have already seen. I must point out a serious flaw in this argument before someone else does. You would expect the surface rocks there to be ejecta, so they likely were derived from deeper layers. But now that I think about it, perhaps a better argument fro leaving would be that it appears that CSM is also mantled in ejecta, so what is the point of wasting time there? Better to move on and learn more about deeper, intact layers. But Tom, those of us in the "Ancient Victoria" school of thought, don't believe that we are seeing, driving over, or ratting Victoria's ejecta. We hold that ejecta is nowhere to be seen. What we are seeing is sandstone that roofed over Victoria back in the Noachian/Hesperian, was subsequently indurated and leached by ground water to produce concretions, and finally eroded and collapsed. I am frantically awaiting close-up views of the uppermost exposures in the capes to see if they are primarily intact, in situ, more or less horizontal sandstones. The latest pancam of "Hoy" looks remarkably in situ right to the top. If close examination confirms this all around Vikky, then I will hold my hypothesis to be supported. I cannot emphasize too strongly that a hypervelocity impact shatters the target rocks near the crater, transforms some into exotic forms, hurls them high into the air and deposits them around the crater with a more or less random orientation of chunks (OK, clasts) in an impact breccia. We saw some of this around Beagle, though that was such a tiny crater that regular impact models may apply imperfectly. I have not yet seen anything around Victoria that I would call impact breccia. Close-up views may reveal it, if we ever get any. Hence my disappointment when Beacon was bypassed. QUOTE Jeff7: Some of us think those dark streaks were formed by the removal of light colored dust rather than dark dust deposition. So, it may be a good place to go for Opportunity's solar panels. I hope we can observe something on the soil as Opportunity passes bay B1, to allow us to determine whether the streaks are due to erosion or deposition. I agree with you on this. I don't see any source of dark material down in Vikky. The only dark things in this area are the concretions, perhaps, and the basalt sand grains when they are cleaned of dust. It depends upon lighting and viewing angles, of course, but in general, what looks darker on Mars is more dust-free. QUOTE As long as I am going off topic, here is the drive direction panorama from sol 1009, as I was able to stitch it. Yeah, I'll let other, more tidy minds decide whether to leave these posts here, or put them in the stratigraphy thread. -------------------- My Grandpa goes to Mars every day and all I get are these lousy T-shirts!
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Nov 27 2006, 09:19 PM
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#20
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Member Group: Members Posts: 240 Joined: 18-July 06 Member No.: 981 |
I don't see any source of dark material down in Vikky. The only dark things in this area are the concretions, perhaps, and the basalt sand grains when they are cleaned of dust. There are dark dunes in the eastern quadrant of the crater that could be the source of the plumes of (relatively) dark dust. The colour doesn't match the average colour of the mantle over this region so I'm on the dust plume side of the debate. |
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Nov 27 2006, 09:49 PM
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#21
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Senior Member Group: Members Posts: 1229 Joined: 24-December 05 From: The blue one in between the yellow and red ones. Member No.: 618 |
I would reply, Mark, that those dunes have been swept free of light dust by the same winds that funnel up through the bays to sweep the annulus beyond. I think it's unlikely, and unparsimonious, to postulate a source of dark mineral existing in Victoria, other than the basalt sands and blueberries that are everywhere else.
Of course anything is possible, but the likelihood is that the whole deposit making up the Planitia Meridiani is about 800 meters of more or less uniform, laminated basalt sandstone, more or less indurated by sulfates, and containing varying concentrations of hematite concretions. Victoria's formation almost certainly did not excavate below these sandstones, and so I would not bet the farm that we will find anything else in the crater. One can hope, but... P.S. "Cry, Havoc!, and let slip the Dogs..." -------------------- My Grandpa goes to Mars every day and all I get are these lousy T-shirts!
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Nov 27 2006, 10:49 PM
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#22
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Senior Member Group: Moderator Posts: 2262 Joined: 9-February 04 From: Melbourne - Oz Member No.: 16 |
P.S. "Cry, Havoc!, and let slip the Dogs..." Err, not Phobos and Deimos - It's the sun. -------------------- |
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Nov 27 2006, 10:59 PM
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#23
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Senior Member Group: Members Posts: 1229 Joined: 24-December 05 From: The blue one in between the yellow and red ones. Member No.: 618 |
Err, not Phobos and Deimos - It's the sun. Rats. I so wanted it to be. So what's the little oval to lower left? Nothing but an artifact? Why can't modern science invent an imaging device that is free of artifacts? Hell, if they can put a man on the moon.... -------------------- My Grandpa goes to Mars every day and all I get are these lousy T-shirts!
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Nov 27 2006, 11:11 PM
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#24
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Senior Member Group: Moderator Posts: 2262 Joined: 9-February 04 From: Melbourne - Oz Member No.: 16 |
Yep, an artifact, go and look at the right eye image taken at the same time, it's not there in that one. It's always worth checking the filter for images like this, 8 (in either eye) is the solar filter and will never be of anything except the sun.
This image is part of an observation of the atmospheric tau at sunset and you can actually see the horizon across the image. James -------------------- |
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Nov 28 2006, 12:38 AM
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#25
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Senior Member Group: Moderator Posts: 3431 Joined: 11-August 04 From: USA Member No.: 98 |
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Nov 28 2006, 01:26 AM
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#26
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Senior Member Group: Members Posts: 1229 Joined: 24-December 05 From: The blue one in between the yellow and red ones. Member No.: 618 |
Yep, an artifact, go and look at the right eye image taken at the same time, it's not there in that one. I thought it was an artifact of parallax that Diemos wasn't there! QUOTE It's always worth checking the filter for images like this, 8 (in either eye) is the solar filter and will never be of anything except the sun. Good tip! Actually I haven't managed to penetrate the MER image labels much farther than the time stamp, without losing my place. -------------------- My Grandpa goes to Mars every day and all I get are these lousy T-shirts!
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Nov 28 2006, 01:30 AM
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#27
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Junior Member Group: Members Posts: 48 Joined: 26-August 05 Member No.: 475 |
There are dark dunes in the eastern quadrant of the crater that could be the source of the plumes of (relatively) dark dust. The colour doesn't match the average colour of the mantle over this region so I'm on the dust plume side of the debate. Hi Mark, I suggest the dark plume material may be originating from inside the crater as suggested in this marked up image: There are two other clearly visible spots around the rim where darker material is also seen: Victoria may have more untold secrets to learn |
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Nov 28 2006, 01:56 AM
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#28
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Solar System Cartographer Group: Members Posts: 10153 Joined: 5-April 05 From: Canada Member No.: 227 |
The usual interpretation of dark streaks etc. like these is not that they are dark material, but that they are places where the regular dark surface of Mars is freshly exposed because bright dust has been removed. The orange-pink dust in the sky of Mars is always settling onto the surface - and constantly replenished by dust devils and occasional large dust storms. So the surface is usually covered with dust as a matter or course.
Dust devil tracks - the DD removes bright dust leaving a dark streak. Steep slope streaks - a small landslide or "dust avalanche" sliding down the slope causes enough motion to expose darker stuff under the surface dust layer. So here in Victoria, the streaks and patches in the post above are caused by small downslope movements, recent small landslides etc. They are not patches of dark material - everything is dark everywhere. But most of it has a veneer of bright dust. And the plumes are places where the dust is removed by wind focussed up the "ramps" - and made more turbulent in the process. The crater higher up the posts does indeed look as if darker dust was deposited over most of it, leaving bright dust exposed only in the sheltered areas. But the reality is still probably the other way around. The wind blows bright dust away everywhere except where it's sheltered. I'm not saying it couldn't occasionally work the other way, but this is the generally accepted explanation. If it's true that in some areas dark dust is being blown around, keeping it from becoming intimately mixed with the bright dust would be very tricky. Incidentally, dark sand dunes are seen in some areas, but sand grains would be hard to get out of a deep depression. That's another issue. Phil -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke Maps for download (free PD: https://upload.wikimedia.org/wikipedia/comm...Cartography.pdf NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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Guest_Edward Schmitz_* |
Nov 28 2006, 02:42 AM
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#29
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Guests |
Bonneville definitely had dark matterial that was forming dunes on the crater floor. And it was blowing up and over the crater rim to leave a dark streak on the plains down wind... It seems plausible to me that there could be a layer of darker matterial that is exposed in the wall of Victoria. That this matterial is eroding and being swept up and out of the crater.
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Nov 28 2006, 03:08 AM
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#30
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Senior Member Group: Members Posts: 1229 Joined: 24-December 05 From: The blue one in between the yellow and red ones. Member No.: 618 |
I agree with Phil's points. I think our position represents one pole of a "streak hypothesis", wherein the dark streaks are formed by cleaning winds. The opposing hypothesis implies that the streaks are "dirtied" by some unusually dark, exotic material eroded from the walls of the crater and scattered across the annulus. Presumably this debate will be soon settled by MIs of the surface outside and inside the plumes.
We could call these two schools of thought, the "Clean Streakers" and the "Dirty Streakers"! I'm sure Ustrax could devise some appropriate mascots. Who wants to sign up? -------------------- My Grandpa goes to Mars every day and all I get are these lousy T-shirts!
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