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

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.

Analyst

Indeed -there is intended investigation of the things around Beagle before heading off again - RN - you've jumped the fun in a serious way

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

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 ?

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?

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 Especially now, we could construct only a very crude model of the interior of the crater.

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

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

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?

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

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

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

Wow - nice MI sequence.....trying to merge with Pancam now

(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

I suppose MMB can help. If not, pointing data on the data tracking web.

I don't believe any placement info for the MI is involved in the PCDB

Doug

very nice MI stitch, Doug !

couldn't resist doing a quick colorization of this one:

I would be really interested in seeing the mini-TES runs as we have approached the annulus and as we embark onto it. If the annulus is primarily hematitic, we ought to be able to determine that fairly easily with the mini-TES.

What will be very interesting is if the annulus does *not* appear very hematitic to the mini-TES...

-the other Doug

Here is the current PanCam view of the sand at our feet/wheels, I'm thinking Sol 914 or so. There is an interesting change in the surface texture-- I can still make out the rounded granules but I'm seeing either angular fragments or flat areas with angular borders between between the granules.

Fooey. Nothing _on_ the ejecta apron, yet, this is from Sol 912 and is an L257 of the ripple trough we were at a couple of Sols ago...

--Bill

4 frames of sol 910 MI pan near Mossbauer press colorized:

Whew, who said flat as a pancake! Here is an L7 Pancam from today showing aeolian and (possibly) anatolian features. I _think_ I have the location spotted on the MOC image, let me post this and go offline to check.

--Bill

That's several sols old....

Sol 912 - 10:38am

Doug

That's "Espanola" (East Hillock) in the forground, and ol' "Jesse Chisholm" in the background, on Sol 912, I believe. A 'Kodak' moment.

Well, duh. You're correct; I was thinking that these "new images" were further along than they were.

Anticipation, I guess.

--Bill

When I saw that sol 912 L7 during my morning MMB update, I nearly jumped out of my seat. I had been waiting for a nice view of the step up to the edge of the apron, and was wondering why we hadn't yet seen a more impressive view of it. At least, that is what I interpret Espanola, and I suppose Jesse Chisolm to be now. Stratigraphically, it looks just like the Halfpipe formation, complete with the overlying layered ripples. The 3D view of it is impressive. As we drove further onto the apron I was seeing all of the dark pebbles between the sparse ripples and wondered why. I was expecting the apron to be totally different. I'll take my geologizing over to the halfpipe topic now.

A quick stitch:

In the lastest Navcam pans, we can see a light-toned area extending to the SE in the direction of Victoria's rim, and this area corresponds to the light-toned area between the windgaps in the crater rim visible on the MOC Route Map image. Close in, we can see that this light-toned material seems to be associated with the transverse ripples caused by the SE wind and we can assume that this light-toned material is likely eroded evaporite material from the rim of Victoria. I'd guess that the prominent dark streaks we see on the ejecta blanket are simply the absense of the light-toned dust. We'll see a a couple of Sols.

jvandriel's Sol 916 Navcam Pan

--Bill

Just been looking at the tracking site for tosol (919) and I see we have this:



Looks like we're going to put a trench in the annulus over the weekend.

Does anyone know if Oppy has done any (intentional ) trenching since the the steering motor failure? I can't remember any. I would imagine that that would affect they way trenching is done compared to what we saw back in the early days.

Should be an interesting weekend.

James

> Does anyone know if Oppy has done any (intentional ) trenching since the the steering motor failure?

I was ready to say "Yes!", but then I saw the "intentional".

It gets more interesting on the ejecta apron. Looking at Phil Stooke's polar of mhoward's Sol 917 pan we can see a network of polyagonal traces on the surface. These traces are a darker and possibly coarser material evidently outlining paving stones of evaporite. The shape is reminescent of the jumbled and eroded blocks we saw around Endurance crater; they seem too irregular and too large to be the typical "mudcracks" we see on the evaporite surface. And the outlining traces seem to have a light-toned core. Hopefully we'll get a series Pancam closeups of these features and this won't be a drive-by sighting.

So it might be that the lighter tone of this location is not totally due to the windblown evaporite dust as I noted a couple of posts up. Based on what we see here, the sandy ejecta soil is quite thin at this spot, so there may be more to the story.


Phil's Sol 917 Polar

--Bill

The surface is so "ironed". Very plane and smooth to ride a surf. The surface has very fine grain covered by small spherules.

Enclosed pictures of Sol 918.

http://marsrovers.jpl.nasa.gov/gallery/all...5JP1785R0M1.JPG

I think that picture is pointing to South azimuth.

http://marsrovers.jpl.nasa.gov/gallery/all...JP1785R0M1.HTML

It is evident the surface has the erosion caused by the aeolian force.

Probably of North azimuth view.

Rodolfo

Here is an L257 Pancam of the spot that Oppy trenched on Sol 918 We don't have a color Pancam of the tranch yet, but I've included an L0 Navcam of the trench. The granules look like Blueberries and the sand is well-compacted/indurated or is a very thin layer. Nothing out of the ordinary jumps out at me, but maybe we'll get some MIs of the soil here.

--Bill

This kind of surface is very easy to drive as off-road. Is indurated and compact as Bill has said. It seems like that the surface has undergone a process of some kind of cementation caused by some kind of chemical reaction.

Do you have any idea about why the surface has got indurated?

Rodolfo

I'm thinking that one sub-cycle of the Martian hydrologic cycle involves frost formation at night and when the frost is heated in the early morning it already in contact with a sulfate salt and briefly makes a saturated "brine" with a low freezing point which soaks the underlying sand and dust. The water quickly evaporates and the dissolved salts cement the sand. The quantity of water is very very small, but this can happen millions of times, daily, over thousands of years and build up to appreciable thickness. We've seen the duricrust almost universally on Mars.

There may be more to it, but this is the quick explanation of what appears to be happening.

--Bill

Bill,

I may have said this before either here or on another forum, but the Martian regolith contains a high proportion of salts such as magnesium and calcium sulfates and chlorides. These are either anhydrous or monohydrates, such as Kieserite, MgSO4.H2O. My understanding is that the hydration state can change depending on the temperature, and it's a very complex multiphase system. I don't think it can get to the saturated brine stage, simply because there is too much 'dessicant'. I think of Mars in terms of a planet sized vacuum desicator. I've worked with vacuum dessicators in a lab environment, and strange effects can result from phase changes, without involving any free water being produced. These include the production of filament-like crystals among other things. The constant diurnal and season variation over a long timescale can produce such duricrust either without any free water, or at the very least, extremely thin films several molecules thick, due to non equilibrium effects.

Well, all I can add to this discussion is that I was hoping we would not yet again see the apparently ubiquitous white stuff. I am not certain that we will really understand it until we dig enough to find and inspect its lower contact. I was hoping for a fresh and deeper roadcut, but apparently this material is quite compacted, and it is difficult to dig through. I discovered a wheel scuff done just prior to the arrival at Beagle. I forgot the sol, but it was only that, a scuff. It found the white stuff just below the surface. Some kind of dessicating salt model might work, but deeper observations are needed.

This is a fascinating planet. Just when you think you have a working model...Wham!

Aldebaran, your analysis is correct, I was having trouble expressing that. I believe that the interaction between water and salts is involved but there is not enough water involved to make liquid anything. I live in the humid southeast USA and many of my views are shaped by living in a dripping atmosphere. In my office I have a piece of pyritic sandstone where the pyrite is reacting with water (etc) to make iron sulfate salts (et al), which in turn pull enough water from the air to sustain the pyrite+water+air=nasty stuff reaction.

But this is the eastiest explanation of the duricrust.

Tom, I don't think we'll ever NOT see white stuff on Mars and even without seeing the chemistry of it I'd suspect that it is a sulfate salt. Sulfides weather to sulfates and unless you have a lot of water to carry it away the salt tends to accumulate. We've see the light-toned material in the looser drifts every time we've cut a trench to purgatory...

Looking at the recent Navcam images I notice that the wheel tracks are light-toned and I suspect that the sand is very thin at this location and we are seeing a reaction zone at the sand-evaporite contact. We need a RAT hole in the wheel scuff.

Again, speculation on my part based on a lot of visual cues/clues and minimal data. Still, the truth will prove to be stranger than reality here on Mars...

--Bill

I was wondering about that. Are we perhaps looking at sulfates at the tail end of this Viking 1 trench? (Or is it, in the words of Roger Daltry, "Just another trick of the light?")

(source: http://photojournal.jpl.nasa.gov/jpeg/PIA00389.jpg)

I think the main reason the surface here is firm and easy to drive on is that the soft, layered ripple material is substantially absent. The underlying material is a good surface to drive on, and I am guessing it is pretty much the same material Opportunity drove on earlier in the trek, before the ripples came to dominate.

After looking back at many of the scuffs and trenches Opportunity has made along the way, I am nearly convinced that this white stuff is possibly best explained by some kind of a salt concentration mechanism, as it appears to be a horizon that cross cuts soil stratigraphy but is not continuous. The thing I am finding most interesting lately, is how looking back at old images leads me to new thoughts. It is very different from chasing the latest images for new thoughts. A lot of information has been collected that I had previously glossed over. There is still a lot of low-hanging fruit.

This is indeed the beauty of having a continuous organized record of mission imagery: if we see something that is significant, we can look back through the earlier images. For example, the surface here is similar to the material around Endurance but not identical. And why does the rippled (or drifting?) material behave differently?

We sometimes complain about not having access to the "chemistry" data, but that is the "meat" to many a paper and thesis so we'll have to be content with the pictorial side of the dataset.

--Bill

The first MI images of the ejecta apron beyond the rippled transistion zone are coming down to the Exploratorium. One of the early images is amazing-- there is clearly a bimodal distribution of the granule sizes; this speaks volumes about their origin.

More later...

--Bill

Bill, one never knows where to post. Re the MI image you have referenced, I would be very interested to know your thoughts on my latest posts in the "Victoria here we come . . ." thread . . .

Actually, Bill, I'd argue for at least a trimodal distribution. Don't forget the fines.

Were they deposited after the coarser grains; or do they represent incomplete winnowing of sediments that were deposited all at the same time?

Well, maybe, technically, but let's look at the granules and not the sands and the fines. So there.

The fines may turn out to be another issue.

Look at the trend to the larger granules to be pyramidal and not spherical or randomly sub-spherical. My initial thoughts are that these may be ventifacts since they seem to have a similar orientation. I'm thinking that the larger granules are "impact lapilli" or tektites, the basalt basal unit that has been melted, ejected and has formed droplets in free-fall. The smaller granules are hematite concretions, the standby Blueberries. The overlying evaporite unit was pulverized by the impact, thrown out as the ejecta apron where it weathered and eroded quickly, leaving the Blueberries behind. Methinks we'll find a lot of fragmented and residual evaporite under the desert pavement here.

My initial theory, but let's see what the Scratchplate shows. And we should be getting more MIs of the wheel trench this evening.

--Bill

I agree with your prediction that the evaporite is probably not far below the surface here. But I'm not sure I agree that the "blueberies" would be durable enough to withstand the impact. We've seen examples of fractured 'blueberries" in other areas. An impact might pulverize them along with the evaporite. Could it be that the blueberries are a pre-impact lag deposit that survived the blast? If that's the case; and if the larger granules are tektites, we might expect to see a blueberry or two embedded in the underside of the larger granules. (If we could turn them over).

--lee

The larger granules which you suggest are tektites reminded me of taconite pellets, the rounded nodules of milled iron ore that are processed for shipping. I'm not suggesting a similar process for their origin - just an interesting coincidence of form.

Here is a panorama of the latest MI in false colors showing the bi-modally distributed pebble field:

Awesome! Normally, I don't care for colorizations, but one can actually believe the real thing would look like that.
Really great work, Nirgal!

Nice colorization! the image speaks more if it has color!

The picture image has called me more curiosity to see all of them. The stone which I suspected most is the ones biggest and with angular edges. However at the top, middle and right of the biggest stone looks like that it has "fossil" marks. Among the spherules, there is five broken spherules (below and left (2) and right (3) from biggest stone). Interesting!

Rodolfo

I find it interesting that so many of them seem to have a little point in the center, and generally facing up.

What else caught my eye: One with a hole in it?