Victoria Annulus, Discusions about Victoria's Apron Options

[dvandorn]

I've gone over all of the recent MIs and I can't find anything I'd call a tektite. If someone would post a picture identifying one of the suspected critters, I'd appreciate it.

I don't know if I'd call them tektites, exactly, but I think the larger rounded bodies in these soils, which tend to have randrop or conical shapes, might well be droplets of impact melt. That would make them similar to tektites in origin and general configuration. But tektites are often formed in the initial blast, from materials near the surface, and are blown a considerable distance away from the impact site. These droplets, if they're impact melt, came from less than 200 meters away. So they were formed later in the impact process (and hence probably contain materials from deeper within the excavation), and were ejected far less energetically than the more far-flung ejecta.

-the other Doug

[CosmicRocker]

Doug: I don't have a problem with the term tektite. I've always assumed that any impact melt droplet that solidified into a glassy sphere or aerodynamically altered shape was essentially a tektite. I see a lot of spheres and a fair number of multiple sphere agglomerations, but I don't see anything that looks glassy, nor anything that looks aerodynamic. I can discount the importance of the things being glassy by assuming they have had time to devitrify or be recrystalized by some later alteration process, but I really don't see anything that can't be more simply explained by assuming that these spheres are simply the same concretions we have been seeing since day 1.

I think I have seen a very few that could be roughly described as conical, but those looked more like multiply-connected berries that were broken or eroded, or berries that were broken from eroded stalks of the evaporite cemented sandstone, like those we saw at Fram. I'd love to see something new, like evidence of an impact melt, but I am not convinced, yet.

[CosmicRocker]

"Tektites" or "impact lapilli" are the best name I can come up with. Unlike earthly tekties they are neither appear glassy nor aerodynamic (for the most part) and unlike earthly lapilli they are't volcanic. They are the basaltic basal unit melted by the impact, assuming a near-spherical shape in the thin atmosphere and falling onto the ejecta blanket. I think the observation of the larger-sized spherules in this locale is important. Look at the L257's taken at this stop, the larger spherules tend to have a color similar to the basaltic cobbles, while the smaller spherules have a slightly different color. I see we have new Pancams of this crater and the distinctive light-toned rocks, so perhaps this will not be a drive-by sighting. Although we'd like to get to the photo-ops at Victoria, we need to do some science at this stop. Understanding erosional-depositional processes on Mars is the key to understanding the geomorph.

I agree with the idea that the holes in the berries are related to the stalks we've seen. And I wonder if some of the berries are not hollow or have a "softer" internal composition (related to Aldebaran's "planar inclusions"). I'm thinking that we see more broken berries here because of the impact. When the evaporite was catastrophically fractured and pulverized by the impact some of the berries were broken along the fracture lines, whereas with slower weathering processes the evaporite matrix breaks around the berries.

By way of earthly analogy, take a look at the attached...

--Bill

I've looked at the L257s, but I really wish someone would post an image with an arrow or two. Damn, I see you have pre-emptivley eliminated two of the previous arguments made in my reply to Doug. Ok. I don't like using terms like "impact lapilli," since it seems to remove the historical connection between lapilli and volcanic processes. Also, these spherules have always appeared to have essentially no internal structure, as opposed to lapilli, which often display concentric rings of ash agglomeration internally.

Correct me if I am wrong, but the last thing we heard from SS regarding the cobbles was this August 2005 quote: "Oh, yeah, and the cobble we looked at with Opportunity isn't a meteorite, it's a martian rock... and one that's very different from anything we've ever seen before. Busy times... "

I've been wondering about the "basal basaltic unit" too. In this part of Meridiani we are supposed to be sitting on top of several hundred meters of "light colored sediment." Victoria surely didn't excavate basalt, unless there is a surprise inside, or unless the impactor was a secondary of external origin.

[Bill Harris]

OK, then explain what we're seeing on the ejecta blanket. There have been several substantial or suble differences in the surface compared to the Meridiani plains. Your shot.

The "dark basaltic basal unit" is the holy grail tying the "oh yeah" cobbles to anything. It may not exist, but OTOH, since we have seen only a few meters of several hundred meters of "light colored sediment", we can't say that it doesn't. Your shot at the explanation...

--Bill

[Gray]

I think Bill might be on the right track. Look again at Nirgal's colorized image of the pebbles:

http://mitglied.lycos.de/user73289/misc/op...24pan_col_d.jpg

Many of the larger grains have a shape that looks like a Hershey's kiss. Some have suggested that they might be ventifacts. But it would take winds blowing equally from every direction to sculpt a grain that way. Unlikely IMO. Bill's suggestion that they may be formed by a melt/impact process makes more sense to me at this point.

One of the grains at the lower left-hand edge of Nirgal's image provides some tantalizing evidence for this idea. The grain is cut by the edge of the image, but you can see that there is a smaller grain (blueberry) contained it a larger grain. It looks as if part of the larger grain has wrapped around the smaller grain.

I'm envisioning a process like this: the meteor strikes the surface of Mars and in the process melts many of the silicate minerals in the crust (it could be a lower basalt or the basalt sands). Molten blobs fly through the air assuming a streamlined, rain-drop shape. The strike the surface while still partly molten. This flattens the bottom but they still retain a streamlined shape in the upper part.
If the grains fell, while partly molten on a surface which was already littered with the smaller blueberries. (A process Bill has already proposed). The under side of the "Hershey's kiss" grain would have the smaller blueberry imbedded in it. That partial view of a grain with the embedded blueberry might be evidence for this.

- gray

[dvandorn]

I think Bill might be on the right track. Look again at Nirgal's colorized image of the pebbles:

http://mitglied.lycos.de/user73289/misc/op...24pan_col_d.jpg

Yep. Please note that in the attached image, there are really four different size populations in the objects we see.

The finest particles are dust-sized, and are consistent with windblown dust particles or the aeolian erosional remnants of local larger bodies which have been worn down by local winds. These particles form the primary portion of the soil matrix at this site, and they resemble (a lot) the fine dust portion of the soil that we've been seeing all along.

The next largest size of body resemble, in size and general shape, the blueberries we've seen ever since Eagle. They seem to be more broken up -- some appear to have started out spherical but have been partially or completely shattered. But these look like the blueberries we've been seeing.

The next largest size of body we see are what Bill is calling tektitic. Most of them seem to have a conical shape, and while the linked image doesn't show this well, many of them have a small depression, pit or hole at the apex of the cone. One would be tempted to say, with a quick glance at the image, "Oh, yeah, those are blueberries." But if you compare their size (larger than the blueberries we've seen before) and their presence in the same soil with smaller bodies that far more closely resemble the blueberries we've seen before, you can see that these are different types of bodies. The conical (or teardrop) shapes seem unlikely to be ventifacts because of the very small size of the bodies and because they appear to have been evenly shaped into regular cones all along their circumference.

There is one larger sized body type in this image, as well -- a more rough-edged pebbly kind of stone that someone remarked (sorry, I don't remember who originally noted this) looks rather like chert or flint. These have multiple fracture planes that form their surfaces, and are significantly larger than either the blueberries or the tektitic droplets.

These four different types of bodies seem to be fairly well mixed in the soil here. But they are definitely all different in appearance, and I would imagine they are all different morphologically.

I'm about 80% convinced that the conical or teardrop shaped objects are some form of impact melt. I don't necessarily have an explanation for why they don't look glassy. I suspect it's a matter of either their initial composition or, more specifically, the volatiles content of the original melt that is responsible for this appearance.

-the other Doug

[CosmicRocker]

Thanks Gray and dvandorn for the image and the descriptions. I'm sorry it took me so long to catch on. At least now I know what you guys are talking about. When I first saw those MI's I thought it was curious that so many of the spherules seemed to have a dimple on the very top. It seemed odd to me that all of those spherules would be oriented in the same direction, but they do appear to have the approximate shape of a "Hershey's chocolate kiss" candy. That was a good analogy to use to describe the appearance for me.

After I understood that, I couldn't help but wonder why we didn't see at least a few of these things tipped over to better reveal that shape. I went back to the original MIs and noticed that several of them captured overlapping areas, thus providing some pretty nice stereoscopic image pairs of at least some of them. I made an anaglyph of the best pair I found, put it next to a similar MI anaglyph NASA/JPL created of some berries at Eagle crater for comparison. I know some of you prefer the side-by-side stereopairs, so I will try to post them as well, or in a following message if they both cannot fit below the forum limit. I think the second is a parallel image pair, so you may need to reverse them if you prefer to view them in crosseyed mode. I am using the excellent program StereoPhotoMaker that was recommended by another member here, and I think I haven't yet learned to force it to make a crossseyed pair.

I think these things we are seeing here appear pretty spherical in 3D, and quite similar to those we saw in Eagle crater. I'd like to hear what other people think, to make sure I am not deceiving myself.

[Bill Harris]

That is what is puzzling about the larger "Hershey's Kiss" spherules. They seem to be oriented in mostly the same direction (point up) and from the very subtle shadows I have the impression they are faceted (ie, quasi-pyramidal more than conical). Therefore, I was initially thinking wind-created venifacts formed in-place instead of tectite-oid features falling and orienting by chance.

I dunno, let me look closer at the "faceted" issue. And after all, we are looking at a sample of a few spherules out of millions. And I'd like to get MB reading to see which spherules are basaltic and which are hematitic.

Any ideas about the rocks exposed in Emma Dean? I keep hoping for a closer look...

--Bill

[Floyd]

If the "Hershey's Kiss" spherules are all pointing up, wouldn't that imply that the soil has never been mixed? Their shape is not so Hershey's Kiss like that they would sort to sit on their bottoms?

[RobertEB]

If the "Hershey's Kiss" spherules are all pointing up, wouldn't that imply that the soil has never been mixed? Their shape is not so Hershey's Kiss like that they would sort to sit on their bottoms?

Perhaps they are blueberries that have been sitting on the surface so long, wind has eroded their ‘tops’ into that shape.

[Indian3000]

CAHVOR color projection L257

R = 80% L2 + 20% L7
G = 100% L5
B = 80% L7

[Indian3000]

R = 100% L2
G = 100% L5
B = 100% L7

[Ant103]

Wow! Delicious colors on the first pic Indian3000, I love it.

[Ant103]

I made a crossed-eyes (or parallel what is the difference between this two?) animation from Sol 917 navcan pictures.

Attached thumbnail(s)

 

[Gray]

Cosmic


Good job on the anaglyphs of the pebbles. You're right, they do look more spherical thanI had originally thought. Now I'm scratching my head again. I still think the "impact tektite" explanation might work, but it's very conjectural.


Indian - good looking colors!