On the Road Again - volume 8 - Page 18

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Author Message
Kye Goodwin


Posts: 1166

Reply: 341



PostPosted: June 3, 2011 12:23 AM 

Barsoomer, re your 339, We might expect ripple movement to "just roll over the berries and cover them with sand", but other outcomes are possible in theory. On Earth granules roll over the surface of sand pushed along by a combination of direct wind and smaller saltating particles. I think that the mainstream visualizes something similar happening with the spherules at very long intervals of time, and possibly under higher atmospheric pressure.

I'm with you though in scepticism. How can wind have managed to create such a strange distribution of loose spherules, present almost everywhere that there is soil, but never betraying a deposit deeper than a monolayer?

Barsoomer


Posts: 344

Reply: 342



PostPosted: June 3, 2011 1:34 AM 

It has also been said that the ripples have become inactive due to being "armored" by a layer of berries, and indeed I think we have seen berries on the ripples.

So how did the berries rise against gravity to get onto the ripples? I guess the mainstream method that Kye mentions is possible, but I still find it difficult to understand how the weak Martian atmosphere could move the fairly substantial berries uphill.

Kye Goodwin


Posts: 1166

Reply: 343



PostPosted: June 3, 2011 1:39 AM 

OK, so maybe Gumdrop could be mostly in soil, not rock, now that I've found a context image:

Gumdrop could be excavated into the edge of a larger crater full of soil. The two smaller craters in this image can't be just in soil though:

The second crater back, upper right, overlaps the ejecta on the rim of the large crater in the background, as Hirise confirms, but the small crater has still managed to become quite smooth inside. I guess that the smaller smoother crater must be younger than the big one with all the bright rock showing?

Kye Goodwin


Posts: 1166

Reply: 344



PostPosted: June 3, 2011 1:45 PM 

Ben, re your 338 and my 337, Yes, erosion rates might be highly variable, but 10 cm in the LAST quarter million years would be a horrendously fast rate compared, I think, to what the mainstream is imagining. For example, here is that Arvidson quote again from a recent Planetary Society update:

"That drive put Opportunity in the middle of an intriguing, "inverted relief" terrain area. "It's an area about 60 meters (196.85 feet) wide that features fractured bedrock with material deposited by wind," Arvidson described. "It [appears] that a little bit of water coming through the fractures cemented the materials and then wind erosion took away the softer bedrock, leaving the fracture standing as high areas, so it's kind of inverted relief," he explained."

It turned out that the inverted relief amounted to something like 10 cm between the polygon edges and interiors, and I think that because the water activity has been visualized as happening early in Mars history that implies a very low rate of erosion of the plains surface. It could be that erosion has just begun here, in the last blink of an eye compared with Mars total history, after nothing happened for billions of years, but I think that relies on too much coincidence.

I think that the ripples may move gradually in some areas, but in others they may just form and erode. The SW-NE oriented ripples have a fondness for developing on pre-existing high points in the terrain, so the biggger N-S ripples might do the same.

Barsoomer


Posts: 344

Reply: 345



PostPosted: June 3, 2011 4:11 PM 

I think I have an answer to what puzzled me about the berries and the ripples. The sand may be packed more tightly, and thus more densely, than the spherules. So if the ground is shaken, the berries would tend to rise relative to the sand in the ripples. Nearby impacts might produce enough shaking, over long periods of times.

[link]

"Pebbles embedded in sand rise toward the surface during ground shaking as a result of convective motions in the sediment."

Rising berries would also tend to produce a monolayer at the surface.

John


Posts: xxx

Reply: 346



PostPosted: June 3, 2011 4:21 PM 

Yo....Fred re. post 332, do you need me to send you a couple rolls of Charmin so you can wipe yourself off? You are just plain rude.

Fred


Posts: 73

Reply: 347



PostPosted: June 3, 2011 9:03 PM 


Well howdy John, been a while since we have heard from you. Glad you are still kicking.
I don’t know about rude? I think it was a priceless question posed to those who don’t “know’

A “rock guy” enigma if you will. Good to hear from you old timer.

LWS


Posts: 3062

Reply: 348



PostPosted: June 3, 2011 9:39 PM 

testing

Kye Goodwin


Posts: 1166

Reply: 349



PostPosted: June 4, 2011 12:18 AM 

Ben, re your 340, Are the ripples covered with spherules or do the ripples move over the spherules? We haven't been calling the ripple armour spherules, so I made a major mistake in my 341 saying that there are spherules almost everywhere that there is soil. In a lot of places the ripple armour includes a lot of spherical particles but they are usually smaller than what we've been calling spherules, around 1mm in diameter, and there are usually other not-so-spherical particles as well. At Purgatory Dune the ripple armour is more than a monolayer thick and to me a lot of the particles look lentil-shaped:

I think that where there are ripples and spherules, the spherules occur in the inter-ripples as you suggest, but I have hunted in vain for evidence of a big plains ripple apparently burying cobbles or spherules along an advancing edge.

Barsoomer, re your 342 and 345, You "find it difficult to understand how the weak Martian atmosphere could move the fairly substantial berries uphill." I sure share your difficulty with this. Experiments and numerical simulations usually predict no mobilization of Mars particles larger than dust, but it sometimes seems to me that Mars science has never seriously considered this possibility (probability really). No winds near fast enough to make sand saltate have ever been observed, but everyone seems to believe that they occur, or that the atmosphere is cyclically thicker, or something. There are "ripples" and doctrine requires hopping or creeping particles to explain them. I think the big armoured ripples will turn out to be something else altogether - more like an undulating desert pavement with differing amounts of dust being slowly incorporated into the sub-armour soil.

Regarding your process of shaking to bring berries to the surface. I think that a number of processes could possibly create a layer of spherules on the surface of soil from an initial mixture: shaking, heating and cooling, wind deflation and lag formation, but that's not really what I need to explain. What about all the situations where there is hardly any soil?:

OK, there are a few bare patches in that image, but they're small compared with the area covered in berries. What process delivered just about the right number of spherules to cover the rim of Endurance in a thin layer? Imagining that there was once deeper soil here and it has blown away doesn't help to explain the overall match.

hortonheardawho


Posts: 3465

Reply: 350



PostPosted: June 4, 2011 8:59 AM 

sol 2616 ( Jun 4, 2011 ) guestimated position:

A record backwards drive?

Ben


Posts: 5

Reply: 351



PostPosted: June 4, 2011 4:53 PM 

Kye; NO, the ripples are not covered with spherules.
I believe the armour consists of a usual thin crust composed of lithic fragments that are larger than the grains in the ripples.
These grains may have been elevated to the surface (as Serpens points out) by thermal effects.
The spherules appear to be concentrated in the flat inter-ripple areas and may not extend beneath the ripples.
You and I believe the ripples are over small ridges which would have tended to concentrate the spherules in the intervening,lower flat areas.

The currently stable ripples have not been inactive for too long as pre-ripple erosion has removed enough rock to release the exposed ,loose spherules.

My problem is that I can't explain the linear ridges beneath the ripples. (wave erosion)?

Serpens


Posts: xxx

Reply: 352



PostPosted: June 4, 2011 9:39 PM 

Ben and Kye Goodwin. Could be a minor perspective problem here. While the navcam makes the ripples look substantial they are in fact tiny as this hazcam from sol 2602 shows. There is no indication here, or in any other part of this epic journey that the ripples are associated with underlying features.

Barsoomer


Posts: 344

Reply: 353



PostPosted: June 4, 2011 10:09 PM 

Ben: NO, the ripples are not covered with spherules.

That seems to be inconsistent with claims made in this paper:

[link]

"Evidence for mechanical and chemical alteration of iron-nickel meteorites on Mars: Process insights for Meridiani Planum"

by Ashley, Golombek, Christensen, Squyres, McCoy, Schroder, Fleischer, Johnson, Herkenhoff, and Parker.

That paper says the following: "The presence of hematite blueberries within hollows on each of the three meteorites confirms that ripples have migrated over the meteorites in the past. The height of their location marks the maximum height of the ripples."

That seems to indicate a clear belief on the part of the MER science team that berries can be elevated and transported by the ripples.

Ben


Posts: 5

Reply: 354



PostPosted: June 4, 2011 11:58 PM 

Serpens; I am not referring to the very low ripples you show, but rather the larger ones shown in past images.
I may be totally wrong (and often am since I propose a lot of ideas) but I don't recall seeing a complete section of a large ripple where one could see what is beneath it near the middle of one.

Barsoomer; I dispute the authors point based on the following.
1. The current position of the meteorites is obviously not where they landed.
2. The most reasonable explanation is that they were once buried by impact into berry laden rock and have been exhumed by subsequent erosion.
3. During the process of exhumation, berries eroded out of the enclosing rock,were captured in the hollows.
4. The ripple are not the source of the berries and if the ripples ever migrated over the meteorites there would be some sand remaining in the leeward side.

Barsoomer


Posts: 344

Reply: 355



PostPosted: June 5, 2011 12:43 AM 

Ben, according to the paper, there is indeed sand in the hollows right beside the blueberries. There is no mention of any sulfate residue as one might expect if sulfate rock erosion was the source of the berries.

The authors of the paper apparently do not think the meteorites were buried and later exhumed. As far as I can tell, they seem to think the rocks landed on the surface, and stayed on the surface except when they were covered by migrating ripples. They also seem to think the erosion that created the hollows occurred due to weathering at the surface.

Perhaps you or Serpens might read the full paper and tell me if I am misinterpreting it.

Kye Goodwin


Posts: 1166

Reply: 356



PostPosted: June 5, 2011 12:49 AM 

Serpens, re your 352, I'm not sure what significance you intend for that hazcam image, or why the size of the ripples matters to this question. The smaller plains cross-ripples are associated with higher underlying features all along the traverse and I'm pretty sure I could make that case to everyone's satisfaction, if you want me to. Here is one example that I've already posted to this thread:

Note how the ripples in the image above follow the subtle higher ridges in the reticulated terrain that Oppy just crossed. (They are longer where the underlying ridges run closer to NE-SW.) I could post many diverse examples of this, but I think that you were referring more to the North-South ripples. I first noticed somewhere between Erebus and Victoria that there are many examples of the bright bedrock surface rising where it disappears under the big ripples and no examples of the opposite case. Here are a few recent images that seem to show this kind of thing:

Ben has noticed this too. I think that there may well be something to this, especially considering the clear tendency of the cross-ripples to form on higher ground. Proving the relationship would involve great software that could extract real shapes from the images and a huge amount of hard labor, because a very large sample would be needed. At least I'm going to start collecting all the suggestive examples that I come across.

Barsoomer, re your 353, and Ben re your 351, I think the answer depends on what we call a spherule. In most places the surfaces of the big ripples show a lot of small spheres that could be the same phenomenon as the larger spherules. I think that these ones in a pit on Shelter Island are almost small enough to be typical ripple armour:

Barsoomer


Posts: 344

Reply: 357



PostPosted: June 5, 2011 1:06 AM 

Another excerpt:

"The dichotomy in Block Island's surface roughness suggests the possibility of prolonged partial burial at some point during the postfall history of the rock (i.e. the smoother portion appears to have been exposed to more erosion). More recent burial and exposure is evident by the presence of blueberries in the hollows to only ~14 cm above the ground surface (but no higher) at Block Island. This observation suggests that at some time one or more ripples migrated over the meteorite up to this height and left the blueberries behind. The fact that blueberries are not found higher than this elevation provides the maximum crest height for the ripples at the time of migration."

The authors seem to have good reason to conclude that migrating ripples were the source of the berries.

Barsoomer


Posts: 344

Reply: 358



PostPosted: June 5, 2011 1:35 AM 

The authors also seem to think the ripples may sometimes harbor ice within them:

"The meteorite is subsequently exposed to water to produce an oxidized coating.... We offer subsurface ice interaction (possibly during ripple migration) as a plausible cause for the production of this dark coating as a weathering product.... The process may be enhanced during periods of high obliquity when water ice may also be stable at the surface."

Serpens


Posts: xxx

Reply: 359



PostPosted: June 5, 2011 3:40 AM 

Barsoomer. Below is the poster session presentation of the paper abstract you link as well as a second poster session contribution on the same subject.
http://www.lpi.usra.edu/meetings/lpsc2010/pdf/1791.pdf
http://www.lpi.usra.edu/meetings/lpsc2010/pdf/2208.pdf
They refer to granular berries and those seen in block island cavities were very small albeit a touch larger than the ripple armouring fragments and grains. Block Island has been subject to acidic groundwater with the implication that it was buried (not exactly unexpected when a meteorite hits) and has since been excavated. Impacting when Mars had a much denser atmosphere Block Island would have impacted at terminal velocity (whatever it was in that environment) and was not a hypervelocity event. It should not have buried all that far. So the bottom half of Block Island could have been beneath ground level when the lag was forming and the conclusion in the poster sessions are due to ripple encroachment seems a bit off the cuff. I would give that conclusion the same level of confidence as their dating the last dune movement by crater count. Pretty much a SWAG (Scientific Wild Assed guess)..
The image below shows the ripples next to Block Island. Berries and heavy grains are in the inter-dune flats, not on the ripples. As Ben says there do not seem to be any big juicy berries on rippes.

Kye Goodwin. I have stared at your images trying to see what you and Ben allude to, but apart from a few isolated instances of protuberances on bedrock at ripple positions (no different to similar protuberances in ripple free areas) I honestly cannot see any indication that ripples are associated with underlying bedrock ridges.

hortonheardawho


Posts: 3465

Reply: 360



PostPosted: June 5, 2011 8:32 AM 

sol 2616 ( Jun 4, 2011 ) L0 3x1 pan in next drive direction:

with a link to a revised guestimated map position.

The guestimated sol 2616 drive distance is now 160 meters.

The revised guestimate is based on pancam and navcam parallax measurements.

The rim of "Young Blocky" crater is now about 45 ( +/- 1 ) meters away.

The plan for sol 2618 ( so far ) does not yet include a drive and the complete pancam panorama next drive drection has not been down-linked , so I'm guessing the move to Young Blocky crater will not happen until late Monday night.

I don't see anything "interesting" on the rim of "Young Blocky" in the single pancam view available so far - so i'm gonna' guess a few quick snaps of the crater and it's back on the bus. Next stop: Endeavour crater!

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