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Victoria Annulus, Discusions about Victoria's Apron
RNeuhaus
post Aug 9 2006, 01:41 AM
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From today, Oppy will start to head toward the Victoria Crater which is about 500 meters away. The drive would take about one month (that is 15 soles of driven with an average of 33 meters/sol, the other 15 soles would be for other purposes or restrictive soles).

The surface around Victoria Annulus, I seems it won't be as smooth as the way between Eagle and Endurance craters but the surface would have no uniform or parallel wave of sand and dust in small size of ripple. See Phil's Victoria Annulus partial map, Tesheiner's one Victoria Crater picture

Otherwise, the surface might have ripples smaller and alike to the ones of El Dorado, on the skirt south side of Columbia Hill. Besides, the Anuulus has no outcrops except to around of few small mini-craters.

This is a change of morphology of surface around the Victoria Annulus. What does it explain about this developing kind of surface of sand? Its extension is just around the inside of Victoria's ray of ejection. That is coincidence. Around that has no bigger ripples as the outside of Annulus.

The explanation would be that around annulus has smoother rock or outcrop surface, no blocks which had not helped to build ripples by the winds. Other factor, I am not sure, is that the slope from the border of Annulus to crater is positive (going up by few meters), then this might be another factor not to build ripples. I have seen that anywhere in the desert that have a slopes does not have any ripples but only flat surface.

Any debate about why the Victoria Annulus does not look like ripples as the outside of Annulus.

Rodolfo
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Guest_Analyst_*
post Aug 9 2006, 06:46 AM
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QUOTE (RNeuhaus @ Aug 9 2006, 01:41 AM) *
From today, Oppy will start to head toward the Victoria Crater which is about 500 meters away.


I am not sure we are done with Beagle yet. I hope we are not, there is so much to learn, more IDD work etc. No need to rush.

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djellison
post Aug 9 2006, 07:06 AM
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Indeed -there is intended investigation of the things around Beagle before heading off again - RN - you've jumped the fun in a serious way smile.gif

Doug
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RNeuhaus
post Aug 9 2006, 02:08 PM
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QUOTE (djellison @ Aug 9 2006, 02:06 AM) *
Indeed -there is intended investigation of the things around Beagle before heading off again - RN - you've jumped the fun in a serious way smile.gif

Doug

Yes, I forgot that Oppy has to collect more data around Beagle. The earliest date to leave Beagle would be after August 15.

Rodolfo
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Nirgal
post Aug 10 2006, 06:40 AM
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Re. the Apron/Annulus: Apart from the orbiter images, I wonder how much can be learned from the
recent set of Pancam shots in the potential drive direction so far wrt. to driveability / dune heights,
surface material etc. of th Apron area ?
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WindyT
post Aug 13 2006, 04:56 PM
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Let's not forget the slightly arcane math question that might be answered by those so inclined:

What's the approximate value in cubic meters of material excavated by the crater, and does it approximately match the Victoria Annulus (the ejecta apron material)? Several assumptions would have to be made about the height profile(s) of ejecta material, and I suppose we'll eventually get to see some interpretations using cross sections at some future date.

I'll add a couple more questions I don't necessarily want answered, but did want to idly ask:

While I'm assuming the answer would be "Not enough information to tell, but probably, 'NO'", is it possible for a measurable fraction of this evaporitic material to really have been be "vaporized" by the initial impact to the extent that it's missing from the ejecta apron material and the surrounding region?

How much got powdered just enough to have been a significant fraction of the dune material outside the annulus that Oppy has been traversing for the last several months?
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algorimancer
post Aug 13 2006, 08:22 PM
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QUOTE (WindyT @ Aug 13 2006, 11:56 AM) *
Let's not forget the slightly arcane math question that might be answered by those so inclined:

What's the approximate value in cubic meters of material excavated by the crater, and does it approximately match the Victoria Annulus (the ejecta apron material)? Several assumptions would have to be made about the height profile(s) of ejecta material, and I suppose we'll eventually get to see some interpretations using cross sections at some future date.


We'd need a detailed topographic model of the entire crater and ejecta (or at least a good quadrant of it) before we could answer that question. I'm not confident that we will manage better than a ballpark figure. Sounds like a good student project, though smile.gif Especially now, we could construct only a very crude model of the interior of the crater.
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dvandorn
post Aug 13 2006, 09:33 PM
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It's also very difficult to estimate the amount of material that was exhumed and deposited around Victoria. You would have to have a good topographic map of the contact between the ejecta blanket and its underlying layer. While this *might* be deduced from a seismic study of the neighborhood (the debris usually has more voids and more lower-density inter-boulder fill within its mass than the underlying pre-impact surface, and therefore has a different seismic signature), I don't think you could do much more than a WAG from the photo evidence.

I don't have the relative figures at hand (and it does vary by impact-target composition), but a certain amount of the target, and nearly all of the impactor, are usually vaporized at the moment of impact -- especially for a crater the size of Victoria. That vaporized material is sprayed in tiny droplets around the local area, and on planets with atmospheres, can be spread preferentially on the prevailing winds. *

As you reach the edge of the region in which the impactor and some of the target are both vaporized, heat and pressure are high enough to melt the rocks. This melt takes on the geochemical characteristics of *all* of the rock types that exist within the melt region of the impact event. It takes on the physical characteristics of igneous rock. This type of rock is typically called an impact melt.

Further out from the center of the blast, the temperatures and pressures decrease through the ranges at which some rock types melt, some are shattered into a fine dust, and others remain resistant to complete destruction. Those pieces which do not melt or shatter become clasts, embedded in a matrix of more easily melted rock. These are fine-clasted breccias -- the clasts in these breccias can be very tiny, indeed.

Even farther out, the impact melt and fine-grained breccias generated closer in to the blast are rapidly propelled through a portion of the target that is broken up, but not melted or pulverized. The still-liquid melts from closer in grab up these cooler rock pieces and make large-clast breccias. In many cases, the clasts in these breccias are pretty much pristine and unaltered examples of the rock that was originally swept up by the melt flow.

These are the kinds of things we ought to be seeing in Victoria's annulus as we traverse it. However, the fact that the Victoria area may well have had an active water table during or after the emplacement of the debris blanket muddies the waters (pardon the pun). The landscape has undergone massive aeolian erosion since the impact, and has possibly (but not definitively) undergone aqueous alteration since then, too. So the rocks will not necessarily resemble the examples we've seen of impact melts and breccias on Earth and the Moon.

* - In re the vaporized material -- it occurs to me that if there was any way to detect the extent of the deposition of vaporized elements from a given impact, we could back-model the atmospheric effects and set some limits on the nature of the atmosphere at the time of the impact. For instance, how thick it was...

-the other Doug


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Bill Harris
post Aug 13 2006, 10:08 PM
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You are correct, without topo and gridding data/capability, these volumetric estimates will be no more that a very WAG. But let me work up some back-of-the-envelope scribbles: Victoria diameter= 750m, depth=120m, ejecta blanket breadth=600m and ejecta blanket depth at crater rim=10m (or less). These are first guess dimensions of Victoria, we can refine them as we can.

Very good discussion, Doug. The impact will alter the rocks depending on the energies involved. This is one reason why I've pushed to get closer looks at the dark boulders and cobble fields we've seen along the way: these are peeks into the cauldron of the Victoria impact. Gathering this data along the way is critical because once we are on the apron and at Victoria the world changes.

--Bill


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WindyT
post Aug 14 2006, 03:43 AM
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QUOTE (dvandorn @ Aug 13 2006, 09:33 PM) *
These are the kinds of things we ought to be seeing in Victoria's annulus as we traverse it. However, the fact that the Victoria area may well have had an active water table during or after the emplacement of the debris blanket muddies the waters (pardon the pun). The landscape has undergone massive aeolian erosion since the impact, and has possibly (but not definitively) undergone aqueous alteration since then, too. So the rocks will not necessarily resemble the examples we've seen of impact melts and breccias on Earth and the Moon.


Oh, excellent, thanks! I was a bit afraid to ask about the current speculation on whether there was an active water table when Victoria was formed -- Is this the so-called "Splat!" scenario I've heard referenced to?
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Bill Harris
post Aug 14 2006, 09:08 PM
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Here are initial (and very WAG) guesses on the volumes of Voctoria and the ejecta blanket, based on the numbers above:

crater 18x10^6 m^3
ejecta 10x10^6 m^3

or, roughly, the ejecta is half the volume with a rim thickness of 10 meters or therefore roughly an equal volume at 20m thickness.

Your guess is as good as mine...

--Bill


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dvandorn
post Aug 15 2006, 06:45 AM
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And, like I said, Bill, the composition of the impact target makes a big difference in how much of the target is vaporized, how much melts, etc. If, for example, the target were mostly jarosite, or there was a thick layer of fairly pure jarosite, it would go from vaporization to pulverization with little melting in between. Some rock types simply don't melt in their primary form -- they pulverize into dust instead. And volatiles content affects the amount of mass vaporized, as well...

However, I rather doubt there was so much jarosite in Victoria's target as to inhibit widespread melting. My understanding is that the jarosite we've found is mostly in the blueberries, and the blueberries do not represent a large percentage of the evaporite down in this terrain. Though, if the blueberries resisted melting and were pulverized into sand and dust instead, that could explain the dark, smooth sandsheet remnants of the annulus.

-the other Doug


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Bill Harris
post Aug 16 2006, 06:14 PM
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Oppy is currently in the transition zone between the ripples and the apron and has done some IDD work: a series of MI and an MB on the ripple face that she turned on and backed up to on Sol 909.

Visible are the subrounded-to-subangular fine gravel-sized particles, plus angular fragments that look vesicular plus well-rounded granules, some of which might be hematite concretions. And, I may be jumping the gun on this, I think I see discrete sand-sized particles (and not silty clumps). We're statring to see changes in the ripple material.

MI Image

--Bill


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djellison
post Aug 16 2006, 07:50 PM
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Wow - nice MI sequence.....trying to merge with Pancam now smile.gif

(nope - can't match with PC - it's all too samey)
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RNeuhaus
post Aug 16 2006, 08:06 PM
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QUOTE (djellison @ Aug 16 2006, 02:50 PM) *
Wow - nice MI sequence.....trying to merge with Pancam now smile.gif

(nope - can't match with PC - it's all too samey)

Almost full of spherules on the Annulus? They are back again as full since Eagle Crater.

Rodolfo
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