"Graham Parkinson" skrev i en meddelelse news:aK_Xb.524264$X%5.482557@pd7tw2no...
I don't think that a similar process occur naturally on Earth. If it should be shaped by rolling on the surface, it would have to be quite light and could also be expected to form their own windblown deposits - tumbling and abration of rocks in the sea-surf tend to make oval and flat rocks. But I do believe that artificial processes like burning wet cement and fertilizer in rotary-ovens tend to make somewhat rounded aggregates. The distribution of the spheres does not seem to me to follow some basic erosional rule (if looked upon as having an average density): to compose a welldefined lag-sediment (* see below), but seems almost randomly sprayed out - but I could be fooled by low-density spheres following wind-dynamic like smaller grains. I believe that some sediments may have two or more grainsize populations ... the second fitting the interstices of the first, but that does not seem obvious to apply on current observations. A 'random' distribution may conform well to an 'ordinary' event like a spray from an impact.
There is a lot of critical comments to add to this, but I'll stick to one: recementation needs replenishment of water.
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(*) The Spirit site achually shows a fair lag-sediment of tightly packed round 'pebbles' with finer sediment in the interstices. If this can be considered an eqvilibrium in current erosional environment, other observations may not yet have reached such 'maturity'
Thank you -- I have it here and will read through it. I guessed you might have been talking about clasts in breccia -- which are rather different in formation, crystallization, etc., than what we appear to be seeing in the "blueberries" at Meridiani. But yes, I am very much looking forward to reading this and I'll make some comments later today. Again, thanks for the link!
Agreed, since so much more information is brought out in the color composites, even if false color, or maybe especially if false color. That montage is made I believe by just a straight composite of the raw images (L2, L5, L7), which means it will greatly overemphasize the blues, but I would pay for that over the red monotone "true color" versions that don't show these intriguing variations.
In the pancam paper available online
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's a chart on page 93 showing the expected exposure time vs. filter used. For the filters used above, the predicted exposure times are L2 (infrared) 0.4 second, L5 (green) 2 seconds and L7 (blue) 10 seconds. So that gives an idea of how much green and blue are overemphasized just by glomming them together.
I think they are using something called Maestro, which is available for download at
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They use that for analysis anyway. However, they only release a limited dataset of images for use with that program.
Well, the guy who did the image above has been working overtime on some great shots, including some great anaglyphs.
Outcrop B&W stitch:
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color stitch:
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movie of Spirit driving:
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of Spirit "track rocks":
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closeup of above:
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sol 39 B&W pan:
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anaglyph of above:
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sol 27 color pan:
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of above:
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Only random ones. Good point about the purple being interesting. Offhand, it looks like the purple is always associated with clearly layered portions of the outcrop, as in this closeup:
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However, the purple is relatively rare. Here's an idea: the direct sunlight is bluish as opposed to the scattered light which is red. The outcrop is reddish. Maybe there are crystalline grains in the outcrop layers that catch the sunlight at certain angles and reflect blue light towards the camera, producing purple (blue+red). Looking at the sun angle in that photo, it seems consistent.
Another interesting "anomaly" is the big chunk of blue stuff that looks like it might be made of the spherule stuff:
Indirectly. According to "Mars" in the chapter on "Aeolian Processes, Sediments and Features," section "Particles and their entrainment by the wind":
"Particles moved by the wind on Mars range fro less that a micron, for suspended dust, to perhaps as large as a centimeter in diameter. The principal mode of transport and size ranges are shown in Fig. 3
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On Mars the particle size most easily moved is 100 microns in diameter, or fine sand. This material is set into saltation in trajectories averaging about 1 m long and 10 to 20 cm high (White 1979). Saltating sand grains may strike larger grains (< 1 cm) and push the along the surface in creep."
Interestingly, on the other end of the scale extremely small particles are also difficult for the wind to lift. Quote:
"Pollack... estimated that the size of the dust in the atmosphere is on the order of 1 micron. This particle size is extremely difficult to set into motion by wind shear alone (Fig. 2)
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but on Earth, is commonly set into motion by saltating sand."
Note that in Fig 2. above the axis labeled U is the laminar velocity right at the surface which is much lower than the free stream velocity above.
Quoting again:
"The laminar sublayer is estimated to be < 9 mm on Mars for very smooth, homogeneous surfaces composed entirely of fine grains (White 1981). Thus, very fine particles, such as dust, would be completely immersed in the laminar sublayer and would be extremely difficult to entrain by the wind unless disturbed, as by saltation impact of larger, more easily moved grains."
"If R > 70, the surface roughness (pebbles, rocks, etc.) become larger than the thickness of the laminar sublayer, the laminar sublayer ceases to exist and the surface is said to be aerodynamically rough."
"Figure 2 shows the threshold friction velocity required to move different size particles with a density of 2.73 g/cm; curves are shown for a range of atmospheric surface pressure and temperatures appropriate to Mars. The increase in friction velocity to entrain particles smaller than about 100 microns is due to aerodynamic effects (e.g., immersion in the laminar sublayer) and interparticle forces. Interparticle forces ay be due to moisture, electrostatic forces and other forces of cohesion..."
"However, once threshold is attained, very low winds can keep dust aloft. Because threshold scales inversely with atmospheric density, the winds required to mobilize dust on Mars are exceedingly high; for example, winds required to move 10-micron grains exceed the speed of sound."
The sand grains which can be seen in the outcrop MI photos in nooks and crannies of the outcrop look to be about the 100 micron optimum size (3 pixels at MI resolution).
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The dust on the surface would be the fine-grained material thus eroded?
Since rough pebbly surfaces tend to inhibit wind transport of particles, could the spherules be protecting their position on top of the soil? Also, some of the microscopic imager photos might show that the surface grains are attracted strongly to each other.
I saw that specimen. If these are the "true" colors, the first thing that really strikes me is that the blue color is highly reminiscent of the mineral azurite. Just a thought.
I'm not any sort of geologist, but I've been vastly enjoying the ongoing discussion on the possible origin of the "blueberries". I don't have all the vocabulary, but the judicious use of a geological dictionary helps me over the rought patches.
It would be interesting to see a bit of the larger context..
Could the circular "berry bowl" simply be an airbag bounce mark?
It takes a little doing due to the difference in perspective but I did identify this region on the panorama. The area behind the rocks (top) is the side of a "dune" for lack of a better word (the loose material at the crater edge). It doesn't look like the lander bounced/rolled that far in that direction.
I can also add that this area is in the original hematite map. The resolution is low, but it is possible to discern that there is no difference in hematite content between the dark spherule regions and that where the lighter shperules are found. In fact, it also appears that, looking at places where there are high concentrations of spherules, that they really aren't the source of hematite after all. Perhaps the hematite is in the sand grains, maybe those blowing in from beyond the crater.
I hate to say it. That is what I've been thinking all along. One of the high resolution images of the spherules contained on spherule that has been battered. On the right edge of that spherule I noticed a small crystal. It was very small, but was obviously not the shape of hematite. Honestly,. it looked more like a silicate than anything else, as it looked tetragonal or orthrombic, not trigonal, as would be the case if it was hematite. Having said that, the resolution wasn't high enough to get a good enough look at it to make any real determination as to what the crystal form actually is. I have a copy of this image, if you are interested. Unfortunately I am not able to access my FTP site at the moment. If you want, I could e-mail it to you.
If the hematite is in the sand grains, what it confining it to Meridiani Planum, an area several hundred miles in extent and reportedly a very ancient surface (> 1 billion years)?
If it comes from the bedrock there, it is naturally confined to that area.
So should we be discussing the sandblasting effect on rounding pebble sized bits of rock broken out of it's original matrix by thermal expansion and contractions? Is there just not enough wind pressure to move marble sized bits of rock around enough to make them spherical?
Graham
I imagine that if the spherules (spheres) protected their position they would become perched on sand grains and then fall off of the sand pillars.
Maybe so, through aforesaid saltation/creep effect.
The idea would be that the spherical pebbles prevent erosion to some extent in the first place by stagnating the air close to the ground, and that such sand that is blown around might collide with them & cause them dogies to creep slowly across the plain?
Rover wake-up theme o' the day:
Keep movin', movin', movin', Though they're disapprovin', Keep them spherules movin', Rawhide. Don't try to understand 'em, Just RAT 'em, 'scope and brand 'em. Soon we'll be livin' high and wide. My heart's calculatin', Gray hematite will be waitin', Be waitin' at the end of my ride. Head 'em out, ride 'em in, Ride 'em in, let 'em out, Cut 'em out, ride 'em in, Rawhide! Keep rollin', rollin', rollin', Though the dunes are swollen, Keep them spherules rollin', Rawhide. Through sand and wind and weather, Hell bent for leather, Wishin' MGS was by my side. All the things I'm missin', Direct from Earth transmissions, Are waiting at the end of my ride.
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