My take on the L456 set:
Click to view attachment

and even better... almost looks like a calibrated image Ugordan, what is it you do?

First I try to get the filter combination to look like what I *think* the calibrated representation would look like, which for the L456 set looks more like a dark brownish-red color for the dust and soil. Then I run that through some code that linearly interpolates between the 3 wavelengths and uses the CIE XYZ formula to generate sRGB outputs. This converts the scene to the familiar rusty orange color for dust and soil - here's a comparison on an early mission sundial snapshot. Final step is then conversion to default sRGB colorspace for web output.

The simple linear interpolation is less sophisticated than a polynomial fit if you have more than 3 filters, but I found it perfectly adequate if the starting filter set is already pretty close to "red", "green" and "blue" colors as is the case with L456. It does a lousy job with L257 stuff on the other hand because the surface spectra is not that flat.

Lots of outstanding images of a remarkable feature! Given how it's standing up, wonder if Oppy could break off a piece by driving over it, to get a fresh surface?

John

The 'true colour' thing is really difficult. For a start everyone's looking at different monitors which represent the colours differently. Just walk past a television shop to verify this. Of course that goes also for the persons creating the images. But there is another factor that I think is even more significant, and that is the adjustment the human eye makes to the ambient colour scheme. This acts to compensate for an overall colour bias in a scene, moderating the perceived colours.

Gordan already knows how much I respect his judgment in these matters so I hope he won't mind me saying that actually I find Stu's colours (as viewed on my monitor) more 'believable' in this case.

I look at these images on an ~sRGB monitor and one that displays ~aRGB and still Gordan's colors (and overall contrast, etc...) look more like the ones on the Pancam site..

I like it! In the past I've advocated deliberately using the wheels to knock things over and look underneath but I never got a seconder for the proposal. Let's see what happens this time.

Yeah. The images on the pancam site don't look 'right ' to me either. I think that's because when I view them I'm not surrounded by 4 pi steradians of Martian landscape. Rather I'm surrounded by a room full of Earthly ambient light. To someone with eyes adjusted to this the Martian scene may indeed look strongly orange-brown. But if you actually went to Mars your eyes would compensate and the perceived colours would shift towards the neutral. I think that's what Stu is trying to represent. (If not no doubt he will correct me.)

somehow (based on some readings; the reproduction of colour by Hunt), I was thinking the colors look oversaturated in photographs just because of the fact photographs are confined to 'a box' surrounded by other light, contrast, etc.. but that in reality, the scene, if observed in real time 'in situ', is just as vivid, only it doesn't strike as being so vivid because it's 'all around you' and adaptation to pure white has alot to do with it. I hope Gordan or others could help me out/correct me on this if I'm wrong.

I don't want to derail this thread any more by getting into another discussion on color which won't really change anyone's mind so this will be my last comment. I never claimed that particular image is really "true" color. The way Pancam DN encoding works, how the raw stretch is applied to both darks and brights in each image, the huge amount of dust on the lens, often significantly varying surface lighting conditions and lacking any stable color reference point in the frame, it's really impossible to claim any accuracy using the raw images. I'm not terribly satisfied with how that image turned out, actually.

Nigel has a point about adaptation to the general hue of the scene, but that doesn't mean color variation is lost to the eye as well. If anything, it should be more noticeable once the overall hue "bias" is removed. Yet I often see images posted where people focus on the overall hue and in the process accidentally destroy color variation in the scene, making the product almost look like colorized monochrome.

Were I boots-on-the-ground there, the second thing I'd do is kick it or thwack it with a hammer. Scuffing the soil with one's boot-toe is a time-honored tradition.

--Bill

That stereography was very informative. With the 3D we can clearly see that the lineations that are apparent crossing the top surface of the Homestake are actually "planar" surfaces extending down into Homestake on an angle. I'm not sure what to make of these surfaces. I suppose they could be faces of individual crystals comprising the "vein," or perhaps compositional banding.

Indeed. And these are not even particularly good quality images. The exposure-- or histogram stretching routine-- is set for an average value of the dark-toned background and almost pushes the light-toned vein material almost through the ceiling. They will no doubt tweak the exposure a bit, and the range quirk will be resolved when the images reach the PDS. All we see now are hints of the full texture.

Today's (Sol-2766) AM images show that the three fragments in the upper side of the vein have a crystalline texture:

http://qt.exploratorium.edu/mars/opportuni...27P2905M2M1.JPG

http://qt.exploratorium.edu/mars/opportuni...27P2905M2M1.JPG

There are 15 MIs of 3 "poses" on tap for transmission today, so we can look forward...

--Bill

Doesn't a vein like that require some long-ago sedimentation process involving liquids?

Precisely, Dr. Watson.

Not sedimentation-- that implies transport and deposition of particles (like sand or silt) by a fluid (like water) in a stream. What we have here is the deposition (crystallization out of a saturated solution) of minerals from a fluid (like water) in a fracture. Called a fracture fill in general terms and is a hydrothermal (and specifically cold-water hydrothermal) process. I'm picking nits, to be sure, but to a geeeologist these are specific and different terms, and we're talking about geology here.

You've heard me babble and talk-in-tongues about this before. This is a major find. By determining the specific types of minerals present here, we can intuit the exact environmental conditions present at the time of their creation.

This is like that erratic we found a couple of years ago, Marquette, that turned out to be a piece of gabbro (peridotite) ejecta that appeared to may have undergone serpentization (a hydrothermal process, alteration, weathering). Sorry, there are a few things in the universe that will make a geologist go bonkers, and this be one of them...


--Bill

And, just stating the obvious, the fact that Homestake sticks up tells us two things:

1) It is more resistant to erosion than the host rock
2) An unknown, but possibly substantial thickness of host rock and vein has been removed by erosion

Googling for images of "resistant vein outcrop" reveals some similar features on earth. If you don't include the word "outcrop" you'll see veins of a different kind.

And on the terminology theme, rather than "sedimentation" it might be more accurate to say the vein mineral(s) precipitated from a hydrothermal fluid.

Bill beat me to it, but I just wanted to add a couple of minor points. Veins are very often created by the precipitation of minerals from liquid solutions, but liquids are not always required. They can be formed by deposition from a vapor as well, so it might be more accurate to say fluid rather than liquid. Furthermore, deposition or precipitation need not necessarily be involved, as a fluid moving through a fracture in rocks can also replace existing mineral in the wall rocks with new minerals.

edit: I just remembered yet another process. Veins can also be formed by the direct injection of magmatic material into country rock.

And here is an image of the rock Yates on Sol-2765. Yates is in the Meridiani-Endeavour onlap zone adjacent to Homestake and hopefully will be one of the areas of study during the winter stopover.

--Bill

Another messed about with portrait of Homestake...

Click to view attachment

Since we have a full set of right filter images of Homestake from sol 2765, I thought I would make a false color, infrared ratio, hematite signature image (hematite should appear as yellow). It doesn't tell us what Homestake's mineralogy is, but it does tell us that the vein is not composed of hematite.
Click to view attachment
It is also interesting to note that there are several spherical pebbles in the left center portion of the image that have the yellow hematite signature, as we had previously seen.

My big fear (apprehension, really) is that the vein will turn out to be calcite. That would truly send our house of cards crashing down! Almost as bad would be quartz, which "shouldn't be" in a Mafic regime like this. It'll be significant, whatever it is.

--Bill

Calcite has a Mohs hardness of 3. Wouldn't that be to soft for this environment?
The way the vein sticks up from the parent rock, it appears harder then that.

Quartz is what it looked like at first glance to me but as Bill said it shouldn't be in a mafic setting i think granitic settings are where it usually lives but granite is rare on Mars so yes it would very interesting if that is what it is. (Quartz needs lots of reworking of rocks I think)
Roy

With the calcite it's not a question of physical hardness, it's that under acid (non-neutral) conditions calcium and bicarbonate won't make the carbonate. However, other carbonates are more possible-- the series of magnesium-iron carbonates (magnesite->siderite) are common around mafic rocks, so the basic recipe is there. No matter what, the composition of that vein will answer a lot of questions (or pose more questions leading to other answers).

Gads, this is like the "who shot JR" conumdrum-- it could go in a half-dozen directions. Matt, talk to your Suits and see if you can toss us a few crumbs as the APXS and MB progress...

--Bill

I'm a little late with this so I decided to kill the solar flare off the IDD as my only contribution...
I used all filters (L2-3-4-5-6-7) and rebuilt the IDD from non flare images with a little C program...
enjoy!
Click to view attachment

This is a geological epiphany.

The more I think about it, the more possible the magnesite->siderite (magnesium->iron carbonate) series seems as the mineral of Homestake. Given that there is a source of magnesium and iron cations as evidenced from kieserite (magnesium sulfate) and hematite (iron oxide) in the area, the ionic ingredients are available. And magnesite is associated with the weathering of mafic (basaltic) rocks and also the alteration of olivine and serpentine (itself a weathering byproduct of basalt) in low temperature hydrothermal processes. This ties it in very neatly with the phyllosilicates on the area.

Here is a "magnesite 101" intro from Wiki:
http://en.wikipedia.org/wiki/Magnesite
and there are beau coup more from a Google.

--Bill



EDIT-- and a couple more tie-ins:

http://en.wikipedia.org/wiki/Siderite
http://en.wikipedia.org/wiki/Dolomitization
http://en.wikipedia.org/wiki/Sabkha

the last one is a real ah-ha.

The Cosmic Log had a nice summary mentioning some of the great work ya'll do:

"Stuart Atkinson, a British educator, author and amateur astronomer who has been working up wonderful imagery from the rover missions for years, produced more than a dozen pictures over the past few days documenting Opportunity's surroundings, and particularly what's happening with Homestake. "

http://cosmiclog.msnbc.msn.com/_news/2011/...rs?preview=true

You seem to have a very nice hypothesis there Bill, I'm now wondering how well that can be tested by the current instrument capabilities.

I recall that the confirmation of carbonates by Spirit @ Commanche Spur required a range of measurements using APXS, MB and the Mini-TES. We have a much clearer target here, with very obvious differentiation in the Pancam imagery, so I don't think the Mini-TES issues are likely to be a problem but will the current limitations with the Mossbauer make it difficult\impossible to be certain what this actually is?

I don't know. The hypothesis is actually no more that a hope and a dream that Oppy will find a particular type of mineral in Hardstake, and that mineral will explain other ideas floating about. Otherwise, this house of cards will come tumbling down (and we'll replace it).

I'm presuming that the APXS and the Mossbauer will be able to identify that carbonate mineral. If not, we'll need to be clever. As we discussed earlier, scuff it with a Rover wheel. A carbonate has a very distinctive and diagnostic crystal cleavage.

After all, I've wandered about for some 40 years IDing minerals with not much more than a handlens, acid bottle and rockhammer...

--Bill

Magnesium carbonate, eh? That's the stuff the building industry should be using instead of Portland cement. (It's carbon-negative.) I can see the headlines now: Cement of the future discovered on Mars!

Aside from the admittedly very exciting discovery of this apparent vein, I don't think that any of our resident geologists have commented on the...uh...tabular nature of the surrounding regolith.

I find this equally startling in many ways. I have seen similar flat pebble overlays on high & dry sections of the Rocky Mountains, as well as in some sections (invariably in elevated locations with respect to the surrounding terrain) of the US Southwest deserts.

I have very, very little geological knowledge, but I have always interpreted such places on Earth as areas of sedimentary rock (though mafic origins are not out of the question, nor is metamorphism). FWIW, I think that interpretation of the surrounding terrain might just shed some light on the origin of this very remarkable vein.

One thing's for sure: We ain't on Meridiani proper anymore. This is a whole new ball game.

Martian Easter egg hunt, anyone?
http://qt.exploratorium.edu/mars/opportuni...2M1.JPG?sol2765

The flat, seemingly interlocking pebbles Nick are likely from a process akin to aeolian "Desert Pavement" here on Earth. (Though there are several other competing theories for the creation of desert pavement beyond the action of wind that wouldn't apply to this spot on Mars today)

"Yates" sol 2765 anaglyph and my3D

New portrait of "Homestake"...

Click to view attachment

...and another vein...

Click to view attachment

Sol 2767 fascinating area who's name we don't know yet because Pancam tracking database updates have decided to take today off, anaglyph and my3D versions:

And in your Comparative Geology FWIW Department, a magnesite vein in Baja California showing the nature of hydrothermal veins:



Caption: Magnesite veins in serpentinized peridotite of the La Costa ophiolite, Sierra de San Andres.


--Bill

Lots of information (I even understood some of it!) on this geology website...

http://www.mindat.org/min-2482.html

... check out the picture gallery. Some of the veins look very familiar...

http://www.mindat.org/photo-362710.html

Just wondering, since Opportunity is quite near to these linear geologic formations, can we say that she has "very close veins?"

No, but one could say:

Abstract:
Rocks of the northwestern Sierra de San Andrés of the Vizcaino Peninsula of Baja California Sur, Mexico, form a partial, dismembered ophiolite sequence. Serpentinized harzburgite with minor dunite, orthopyroxenite, and pediform and disseminated chromite comprise the ultramafic section. Ultramafic rocks of cumulate origin are absent. An interior mélange of sheared serpentinite contains exotic blocks of altered serpentinite, metavolcanic, and metasedimentary rocks which range from greenschist to probable high-grade blueschist facies. A disrupted but intercalated section of layered clinopyroxene-plagioclase ± olivine cumulates and olivine melagabbro cumulates overlie the ultramafic rocks along low-angle faults. Orthopyroxene (bronzite) is the major intercumulate phase in the olivine melagabbro. Non-cumulate uralite gabbro is exposed in isolated fault blocks adjacent to the cumulate gabbro. Hornblende-bearing plagiogranite locally intrudes the uralite gabbro, resulting in an intrusive breccia. Plagiogranite with a diabasic texture composes another fault block which may be part of a sheeted dike or sill complex. At least 400 m of microporphyritic plagioclase ± clinopyroxene pillow lava is exposed. In addition, small scattered fault blocks of plagioclase ± clinopyroxene spilite and keratophyre may represent rocks derived from a deeper level in the complex. Pillow lava is conformably overlain by tuffaceous shale, friable Buchia piochi-bearing shale, potassium feldspar-poor volcanic arenite, conglomerate and pebblestone of the Upper Jurassic Eugenia Formation. The Turonian middle member of the Valle Formation overlies the ophiolite along low- to high-angle faults of small displacement. The ophiolite complex is cut by a west-trending shear zone and by northwest-trending faults. The latter are probably related to the Cenozoic right-lateral fault system of the northern Vizcaino Peninsula. Chemical analyses of ten gabbroic and volcanic rocks exhibit low K2O content and AFM trends characteristic of other ophiolites and abyssal tholeiite. This, together with stratigraphic evidence, suggests that the ophiolite is a piece of remnant oceanic crust which formed close to the Late Jurassic continental margin. It is suggested that prior to emplacement, the ophiolite formed the trenchward part of the upper plate of a Jurassic subduction zone. As a result of water derived from dehydration of the down-going oceanic crust, serpentinite diapirs formed in the mantle above the subducted plate and rose upward to a position below the overlying oceanic plate. The emplacement of the diapirs may have produced Cretaceous and Tertiary uplifting of the Vizcaino Peninsula.

http://sdsu-dspace.calstate.edu/handle/10211.10/201

about that photo I posted earlier and supppose that this spot on Mars has every bit as complex a history.

--Bill

I think so, with every Cape there's a Capillary

Found it!
Click to view attachment

Interesting series of 6 frames from the left and right pancams.
Wonder what the science was?

Click to view attachment Click to view attachment

Good job!

I wondered the same thing, since we already have a full pancam series of all of homestake.

The small subframe images were taken interleaved with the larger Pancam set, in the same pointing. But I am clueless as to why.

Hmm. Now that you mention that, I remembered the Galileo SSI team used to do that sometimes. They'd return the whole image heftily compressed but sometimes resent back one small area of interest at much lower compression.

These were actually separate images, for each filter the tiny one taken just after the regular one, IIRC. But yeah, compression is the only thing that springs to mind? Or maybe some really obscure detail to do with the brightness of the subsection. Or something we haven't thought of.

Has it been determined that Homestake has been tipped by some process or (combination of processes) such that they are now standing like an underground stone fence?

Edit: voting for Northeast-facing winter parking spot, thinking of the winds flowing inside the big crater.

Ahh, well that's a big clue then. There were no pancams or navcams taken of homestake after the 2763 move until the full-view pancams and interleaved tiny subframes on 2765. Therefore they had no way of knowing where to crop the full frame images to get the tiny subframes perfectly centred on the vein of homestake!

So that suggests to me that this was a test of some method of figuring out how to crop on a target when "blind". One idea is that they built a model of the surface in front of them based on the images from the previous location or based on the front hazcam from after the 2763 drive, and used that to guess where to crop. Another idea is that they used some code to "find" a part of homestake to crop out, kind of like how they crop on the Sun. My guess is the latter.