The proposition that Mars was once Earth-like in climate is no longer a proposition. The possibility that Mars might not have been Earth-like is no longer under consideration. Warm-wet Mars has become a belief.

Indeed, we understand a fair amount about the current surface conditions on Mars. Most of the debate here has been centered on which geological processes were active on Mars when these sediments were deposited in Meridiani Planum. The rocks are thought to be of Noachian age, dating back to the time of heavy asteroidal bombardment prior to about 3.5 billion years ago. Unfortunately, we have very few examples of rock preserved on earth from that early time period to use to develop models for the kinds of conditions that exist in the early stages of rocky planet evolution.

Mars seems to have preserved a much better geological record of that early period of development, and hence, the evidence we observe there is very intriguing, and also quite debatable. That's why I prefer to not see the discussion artificially limited.

I entirely agree with you Kye. However, from what we have seen so far and from what we have learned about Earth's past, the notion of a once wet and warm Mars is a possibilty. On the other hand we must also prepare ourselves for the truth. Even if it is against our 'beliefs'.

Don Burt--

I know Im not supposed to mention this debate ever again (courtesy of the Admin), but it occured to me that the Athena model for Meridiani can still account for the features of the blue berries; the crystallization going on during the formation of the bed rocks could have regulated the growth of the blue berries to produce such regular spherules.

And how does the Impact surge hypothesis account for the occurences of 'vugs'?

You mean like the belief in surficial berries? Goodness no. There is a huge difference between belief systems and the outcomes of scientific research and analysis. The impact surge argument has dragged on without the protagonist addressing key questions such as how the Meridiani layers can overlay the craters which are supposed to be their source and the other problems with the theory that are set out in the Grotzinger paper that you you posted. Doesn't it seem strange that we can accept and Earth that oscillated between 'Iceball' conditions and the environment that could lay down the vast coal beds that we are currently exploiting, but the concept that Mars also experienced a huge climatic swing is shouldered off as a belief system.

The statement from HDP Burt that 'in this type of detective work, an open mind is a prerequisite; groupthink, unwarranted assumptions, and preconceived notions are the enemy.' is absolutely and fundamentaly correct. But perhaps a little navel gazing on the assumprtions and preconceived notions associated with a Mars that has had no inflence other than impact is in order.

Watch it guys - this thread is getting a bit personal, and is certainly going back over the old ground that we've closed up elsewhere. The use of absolutes ( it can't be this, it must be this, it's never been this, it's always been this etc etc ) is just plain ignorant. We are basically going back over the same ground, two camps that don't see eye to eye. Don't make me close this thread as well because it's crashed into an infinite loop.

If you really really want to carry on in that way, do it elsewhere, or via email.

Doug

What are the odds of the victoria impactor or fragments of it being at the surface? Apologies if this has been discussed previously. Do we have any clues as to what kind of rock it was?

Victoria shows all the earmarks of having been a primary impact crater -- created by an impact by a meteor, not by ejecta thrown out by another crater somewhere. As such, the impactor was almost definitely entirely vaporized upon impact.

The complete lack of impactor fragments at Barringer Crater proved rather conclusively that impacts of that size and energy always vaporize their impactors, leaving no rock left to study.

-the other Doug

Aussie, re your 505, I am just expressing my dismay that the rover team seem to have reduced their considerations of Meridiani to a single hypothesis that requires Earth-like conditions. This might not turn out to be realistic. There is a much simpler explanation on the table.

In fairness, I have oversimplified. Some rover scientists, Yen in particular, have explained some of the evidence of aqueous alteration as the result of weathering processes that could take place under current conditions.

I avoided commenting once it appeared I had again come up against something resembling blind faith, but will state, in strong support of Doug E, that these matters all were covered in our original peer-reviewed 2005 Nature paper, and multiple times in the ensuing long discussion thread. Nevertheless, I'd be happy to go over them as a response to a private message, if you send me one.

BTW, just because something possibly could have happened, doesn't mean that it did. In science, as in any other detective work, you commonly have to evaluate competing possibilities. (Popular example: just because you lack an alibi for the time of the killing doesn't necessarily mean you're the killer.) This evaluation is not easy or trivial. It requires broad experience and a certain amount of intuition and luck. Aside: Who me? Reads detective stories?

-- HDP Don

I've avoided commenting too, but here I think you're being too pessimistic. I (and I'm sure others here) have absorbed your message and have it in the back of our minds when new scenes and new findings appear. Just because Doug doesn't want it endlessly recycled (at his expense) doesn't mean that your ideas have been banned. In fact he's done you a favour by hosting so much discussion. Just for the record - I didn't vote.

In my original post #457 which mentioned varves, the point that I perhaps should have emphasized is that to me the regularity of the layering would seem to be associated with an annual process -- which I suppose is not ruled out by the Grotzinger et al. scenario . . . just for the record.

Thanks, ngunn. I wasn't referring to this group, but only to very few individuals, and I did not specify which side of the ping-pong table they were standing on. I much appreciate being able to find a forum of bright, outspoken, critical, well-informed, and above all enthusiastic individuals here. All scientists should dare to try it. However, as the detective, lawyer, or judge might say, "just stick to the facts, please." That is, please document any assertions, because I simply don't find what sound like general statements of belief (whether they're intended as such or not) useful for doing science. It would be the same if I were a juror in a legal case.

-- HDP Don

AFAIK, it's not included in it either (someone correct me if I'm wrong). Regular layering is quite common in many types of sediments, whereas varves seem to be a rather special case. They only form in lakes that freeze over for half of the year, and thaw for the other half, and no lake beds have yet been identified at Meridiani. That's not to say that Mars, with its extreme seasons, doesn't or didn't have something analogous. If so, such a feature hasn't been recognized yet, and does not appear to be required by any surficial observations to date. (My guess would be that any old varved lake beds, say deep in Gusev Crater, are buried under younger debris.)

-- HDP Don

I've seen significant speculation that Mars has tilted on its axis pretty severely over its history, meaning that some portions of the planet that are currently equatorial may once have been located at a pole.

Has a polar deposition origin ever been suggested for the planar layering at Meridiani?

-the other Doug

If I remember well, the initial theories about Meridiani (before MER got there) was that melted water from ice seeped underground and was boiled by underground heat. The result is haematite deposits.

From the looks of things the possibility of polar deposition origin has not been considered.

Other Doug - That sounds like a really good, original suggestion. If the ice gradually sublimed, without melting, annual dust layering could be preserved even as ice evaporated and the section got thinner. A way to test this hypothesis would be to look for similar layered deposits in the vicinity of the present-day poles. A fly in the ointment might be if the dust were remobilized (picked up by the wind, especially katabatic winds of colder air flowing radially away the poles) after its ice cement had sublimed away. Hygroscopic (moisture-attracting) salts in the dust might impede this by making the dust somewhat sticky. Low angle cross-bedding might be produced if the if the year-to-year wind erosion were somewhat uneven (so that summer erosion locally cut across winter additions). For application to Meridiani, how would you produce the blueberries though?

-- HDP Don

...or the festoons?

Shaka, Regarding festoons, Please see Page 1, figure 1:

http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1757.pdf

Dr. Burt, I have been thinking about Meridiani in light of the impact theory for more than three years but have had little chance to discuss the scene with others considering a similar model. One intriguing phenomenon that I have puzzled over, is the large number of so called "ghost" craters like Vostok, Erebus and Terra Nova. Many more very shallow craters are visible nearby in MOC images. Here is a quote from: The Relative Ages of Geomorphic Features Visited By The Opportunity Rover; Parker, Grotzinger and Athena Team:

"Terra Nova and Erebus likely formed "near" the end of deposition of the outcrop material. These craters clearly predate the surface exposures of the outcrop, because the fine laminations are present all the way up to and within the rims of both craters. Erebus crater is only 5 meters deep, and effectively rimless, and Terra Nova doesn't exhibit any obvious depression at all. Outcrop can be seen within both craters from orbit and on the ground, so the two craters must have either been nearly completely filled in by outcrop deposition, or their primary topography has been destroyed by eolian erosion or both."

http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2312.pdf

I know that this may not be the friendliest forum for informally kicking around ideas, but I was hoping that you might have some conjectures you would be willing to share about the possible history of the ghost craters in an impact sedimentation model. What is Erebus Crater anyway? I suspect that the original crater has been not just filled but also shallowly buried by surge, and that the escarpment and half-pipe at Payson lie entirely above the original crater.

Definitely not festoons. The "T's" are not there. Sorry.

Despite a famous sedimentologist claiming, after seeing the photos, that they had to be water laid (rain water eroding the top of the surge deposit)?

Edgett (2005, Mars Journal) concluded, on the basis of orbital images, that cratering coincided with sedimentation at Meridiani. Most people assume that old ghost craters, wherever seen, are buried, whether by younger lava, sediments, or various types of impact deposits. This conclusion would be unaffected by whether or not sedimentation were caused by the cratering process itself. Some Mars craters appear heavily eroded, but these are generally the oldest ones, not relatively young ones towards the top of the stratigraphic section. So burial seems somewhat more likely, despite the friability (lack of inherent strength) of the Meridiani target. That is, a crater formed at that time should have been buried before it had too much chance to erode (although it could have rapidly gotten larger and shallower from wall collapse).

What make surge potentially interesting is that volcanic surge deposits, and by analogy impact surge deposits, can sometimes be deposited with original dip (true bed inclination, different from dune cross-bedding) owing to particle stickiness (that is, you might see their bedding drape over an old crater, rather than simply fill it, or go around it). Such original dip appears evident in the surge deposits at Home Plate, for example, whatever their origin. Of course, water or wind deposited sediments might appear to drape over an old crater owing to later compaction and dewatering, and ice sublimation could cause a similar effect. So something that appeared to be original dip might be deceptive. You'd have to look for a single thin rock layer that had never had other sediments deposited on top of it and that ran down one side of a crater and up the other side (probably with considerable thickening and dropout of coarse material in the bottom) and then continued to overide the blocky ejecta. This might only be visible for the youngest deposits. And I'm not talking about a passively settled dust layer here - you'd probably want to examine the rock up close to verify abundant low angle cross bedding in sand rather than simple layers of dust. Are you paying attention, HiRise fans?

Water generally doesn't flow uphill. Wind can, but it generally drops most of its sand at the bottom of the hill (unless it is a very dilute dust storm, in which case it drops very little of anything anywhere on the hill). So surge might be distinctive. Just a thought.

-- HDP Don

tap tap tap

Hello....is this thing on?

http://www.unmannedspaceflight.com/index.p...st&p=107948

And in the beginning God created the Heavens, and the Earth, and all manner of creatures therein. And this entire evolution took just 6 days and takes up 2 pages of the King James 1 version of the bible. Seemingly the remaining 1,732 pages are devoted to discussions of impact surge.

Don Burt – your dialogue on the interpretation of field evidence is very appropriate for these discussions, and your post a week or so ago on festoon geometry (on a closed subject matter) was especially right on, every geologist should take a course on how not to be fooled by apparent folds or flexure when viewed in the field. HP is a good example as you point out, the dip we see may be real or apparent. Water GENERALLY doesn’t flow up hill – is that one of those new rules of Mars?

http://en.wikipedia.org/wiki/Internet_troll :

Long-time readers would both recognize the poster's name and know that the topic had been done to death already, but new subscribers to the group would not realise, and would thus respond.

http://en.wikipedia.org/wiki/Thread_hijacking :

Thread hijacking in internet forum communication is the act of steering a discussion off-topic by discussing a subject entirely unrelated to the subject at hand.
While this can be an intentional act of trolling, it is often accidental - caused by participants in the discussion responding to a throwaway remark.

Nuff said.

Hey, I didn't bring up or even use the f-word the last time, but I did notice the smirk emoticon that followed its use, and so didn't take offense.

Regarding water flowing uphill (throwaway remark), try using a forceful garden hose on a child's slide - you can do it (although I have to admit I haven't seen any garden hoses lying around in the MER photos). A forceful outflow channel flood might do it too - I wouldn't want to be standing on top of a hill in the center of the channel, or looking down from the outside of a bend, at flood time, given the low gravity. A hot spring or geyser does it also. Finally, an upside-down siphon analog (underground artesian system) should be able to do it. People have seriously proposed various kinds of uphill water flow to explain Meridiani, not to mention the silica-rich rocks near Home Plate, so please don't mock the concept.

Also regarding water flow, I'm off to babble about brooks, or possibly about small downhill flows of frost-leached eutectic brine in gullies on modern Mars, in Houston next week. I'll be sure and report back if anyone talks about uphill flow.

-- HDP Don

Clouds drifting by on sols 1413 and 1429. I've used each series to construct a flatfield mask by averaging the frames and then I divided each frame by the mask. So the result is really too flat - where there are no clouds the sky appears uniformly grey, and any true sky brightness gradients are removed. But the clouds are very visible.

Frame interval is about 400 seconds on sol 1413 (so it can be hard to follow the movement) and about 30 seconds on 1429.
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And 1429:
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Anyone else noticed the part of the recent description of the Lyell Panorama, to whit: They are "Cape Verde," about 6 meters (20 feet) tall, on the left, and "Cabo Frio," about 15 meters (50 feet) tall, on the right. This gross difference in height was never apparent to me, though I can't claim to have done any measurements. Is there an error here, or is poor, confused old Shaka just befuddled as always?

http://www1.istockphoto.com/file_thumbview...in_ice_sign.jpg

The two peaks probably are at the same altitude, but the foot of each cliff is not.

Perhaps the easiest way to see this is to look at a contour map, for example one on this page. You can see from the map that Frio sticks much farther in towards the centre of the crater, so the floor below it is much lower than the base of Verde. This hasn't been obvious from the rover imagery because we've always been closer to Verde than Frio.

Actually, from our sol 1155 position (way over on Tierra del Fuego) we were about the same distance from Frio and Verde, and you can see in this navcam shot that Frio is much taller than Verde. I've identified them in this image:
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Wow! That makes it pel..lucid. Thanx, Freddo. Frio is now doubly attractive as a study area, assuming the slope is negotiable.

What is the story on the 'Gilbert layer'?
The MER were supposed to discuss on this.
How come I can't see it? Can anyone help the blind man see more clearly?

Super-flatfielded clouds drifting by on sol 1433:
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Colourised from today's pancams...

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... and another...

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Doc: On sol 1419 Opportunity took a 5x3 color and 3D pancam panorama looking deeper into the crater. Those images were labelled as "pancam_Gilbert_5x3_L257R2." The set of images essentially was pointing at the nearby area of sand and berry covered layers below the Steno-Smith-Lyell layers. If you use MidnightMarsBrowser, that panorama will be easy to identify. It appears to be different from the apparently diagenetic layer above it. It is a very tempting target from my point of view.

I must believe the team would like to study these deeper layers before exiting Victoria. Although the sediment covering these layers would reduce the rover's traction and challenge the RAT, the slopes in this deeper area appear to be a bit less than those already traversed.

Thanks CosmicRocker.... now I can see...

The Gilbert layer seems to be origin point for these 'razor backs'.
And its certainly covered with muck(the thickness of the dirt on the layer is apparent in places where there are cracks).
It is an interesting target like u said.

Also check Tesheiner's excellent labelled closeup routemap to see Gilbert in context.

They've started to update the updates! From this one we have the shocking news that the dust storm has made a surprizing comeback:

I think they meant "hovered between 0.7 and 0.8"!

Also, from this one, a nice description of a sol in the life of Oppy:

It appears that on sol 1438 Opportunity drove a short distance down to the upper part of the Gilbert layer, and positioned the IDD above it.

Thanks for the heads-up, Tom.
I'm updating the map right now.

Given that Stu's recent posts #539 and #540 show the Meridiani layering in exquisite detail, and given that I may perhaps have something new to add to the discussion -- and indeed, if the topic is Meridiani, you really HAVE to talk about layering -- I venture the following: In his 1983 article on "Life" for the 15th Edition of the Encyclopedia Britannica, Carl Sagan writes that

"While large open pools of pure liquid water are not expected on Mars because of the low atmospheric pressures, briny pools in salt deposits are possible, and there is some reason to believe that liquid water may form temporarily each morning on Mars in soil interstices where the vaporization of water is limited by diffusion."

Now I am not citing Sagan here as the all-knowing -- after all, he was writing 25 years ago -- but to the extent that he was reflecting the mainstream of exogeological thinking, which seems to have been somewhat endorsed by recent findings, it IS rather interesting to look at the pictures in Stu's posts. During the summer months there will be more moisture creeping to the surface, thus forming an annualized crust. And the mechanism of the dips and hollows left by shifting sand dunes would seem to me a perfect explanation for the irregularities we find in the layers.

Another move was scheduled for today, sol 1441, so we might have some fresh pictures from a new site in a few hours.

Definitely not an area to fall over in when wearing a spacesuit...

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...what the hell is going on here?! Looks like erosion, of course, but why the blades at the interface???

At the risk of incurring the wrath of my fellow UMSFers, this looks like an artifact of an active process, possibly involving fluids, or at least atmospheric moisture; damn!!!

Big-time shooting from the hip, here; are the blades gypsum? Also have to add that this is by a long shot THE most astonishing image I've seen from the MERs; thank you, Stu!!!

Close-up...

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