On the Road Again - volume 4 - Page 14

Kye Goodwin. I have noted a bit of backtracking and excuses (sorry- explanations)going on with regard to the 1,000 year crater statements. I think they leaped in, possibly basing the initial statement on the fact that dark rays were visible around the crater in HiRise images. Well closer up this is shown to be erosion of directional ejecta deposition that could have taken a long long time to erode. The fact that ejecta sits on the large dunes is no indication of a very recent impact. Where do they come up with these things?

I also am not sold on the underlying methodologies used to decide that the ripples last mobilised aroung 100,000 ka. A touch of Ptolemaic reasoning in that model.

serpens, re your 257, I hadn't seen your post before I posted my 259 so we are thinking independently along similar lines. Erosion seems inexplicably fast if this is a very recent crater.

Thanks for your comment regarding my 256 about the downward trending berry stems. I've been wondering if the erosive process creating the stems might somehow involve air movement up the faces of the block. I don't think that saltating sand grains could turn upward in flight on such an air current. Suspended dust, tiny ice crystals or water vapour could follow such a path with the air. I imagine an air movement that is low-speed and occurs daily affecting the distribution of traces of water and dissolution of the rock. Levin has published a very interesting theory in which a thin layer of water-saturated air develops against the surface just after the local sunrise starts to sublimate the nightly frost.

folks>>>

Did we ever discuss the 'time-line' of the blueberries...since it was made until its 'dust' into blueberry erosion as proposed here?

yt
dx

sol 2143 ( Feb 3, 2010 ) L0 5x1 pan after 5 meter move towards the NE - away from Concepcion:

Er, what?

Does this move make any sense? Does any of the study of Concepcion so far make any sense?

Re eroded blocks:
Differential erosion rates caused by volatiles (ie water-ice) packed among the sandy layers could skew the apparent time-line. In this scenario, the newly exposed volatiles would quickly melt/sublimate, enhancing the appearance of long-term erosion. Possible, but not likely?

Serpens, "timelines" are geomorphological thingie. It means "we really dunno, let's assign an order-of-magnitude value" to it and mumble knowingly. It mean, anywhere from 100 years to 1000 (or maybe 10,000) years. It's geo-horsepucky if you make a definite statement on it.

During the 30 year sor so we've been on this photographic survey of Mars, we've discovered over 100 new craters with the MOC/MRO Context cameras. I've not done/read the stats on this, but the recurrence interval for craters of this size can likely be measured in decades, if not years.

Weathering and erosion of the Burns Fm is rapid. The rock is soft and is eroded and transported quickly, probably within decades. On non-meridiani rocks (like the standard basalts) the weathering rate could go up 2-3 orders of magnitude, as could the ages of the craters, based on ejecta appearance.

I think that the wind erosion and transportation rates at this site are generally underestimated. Look at the degradation of the Rover tracks as we've backtracked around Endurance and Victoria. Look at how quickly the disturbed sand at Purgatory was blown by the wind.

--Bill

> That's on the order of ONE CENTIMETER in 1000 YEARS?

Why is there the assumption that the erosion has taken place only since the impact? Perhaps rocks that were eroded over eons were buried and then exposed by the impact. Or maybe the erosion took place underground before the crater was created.

Concepcion does seem to be different from all the other craters we have visited in one respect: There are far more small pieces of breccia visible than at any other crater. I'm inclined to accept that this is the freshest crater that Oppy has visited but l'm not very accepting of the proposed absolute age of just 1000 years. It sure would be nice to know for sure the age of anything in Oppy's world. Then maybe we would have someplace to start.

Barsoomer, re your 267, Yes, we would have to do some sort of statistics on the whole pile of breccia before pronouncing on the extent of erosion because some of the material would have been on the surface before the impact. I think it is a reasonable assumption that the differently eroding layers started out flush after the impact but it is far from certain. If this is an example of an impact into material that was already eroded breccia then we're hooped, but I judge this possibility unlikely. If the layers eroded underground that would be chemical erosion for sure and an important discovery, but we don't have much evidence to go on for that one. The combination of deeply indented layering and multiple long berry stems on multiple blocks makes the case for post-impact erosion quite strong.

Bill Harris, re your 266, I think that one resolution of the paradox of the rapid degradation of Rover tracks in the same environment as ancient inactive ripples is that dust moves all the time and produces small incremental changes, while sand-sized and larger particles are moved very rarely or not at all under present climate conditions. Rover tracks are easily camouflaged by dust deposition but where the rover wheels have pushed up ridges of coarser particles there may be evidence of this for a long long time.

I agree that there is a dating enigma to be resolved somehow.

Kye, Bill

Lots of interesting observations and insights have come up in this discussion. Indeed, I think it is arguably one of the most important discussions held on this forum re. really understanding meridiani.

The crater dating enigma; I suspect that the dating of 1000 years old is way off. Why? Because there are several observations, most at Purgatory and a few near Victoria crater, and even in the Heat Shield "crater" that suggest that erosion or soil filling can take place very rapidly.

Here are just a few of my images from purgatory (sol 495 or thereabouts) or the Heat shield (around sol 300) that suggest this;

-To be continued-

Winston

Those are the images I was thinking about.

In the big jigsaw puzzle of Meridiani we're finding several key pieces that we can start moving others around.

--Bill

sol 2145 ( Feb 4, 2010 ) saturated color of target "Loboc River":

with several links, including super 3D views of the blocks.

Ah. The move yesterday was to line up for approaching these very interesting blocks on the rim of Concepcion. The move scheduled for later today shoud bring these blocks into the working volume of the IDD.

I had forgotten that the limited mobility of the arm now means that Oppy has to compensate by moving the entire vehicle before IDD studies.

And Oppy is making cautious moves here-- remember, even though the ripples "look undisturbed", they are covered with fresh, disturbed material, so we're not sure what the surface/traction will be like. And we are moving cross-ripple, which is risky in it's own right.

I'm seeing some deep blue chips on the surface-- possible impactor fragments?

--Bill

sol 2144 180 pan looking south towards Concepcion and 180 pan looking north away from the crater, with 3d pairs.

The most interesting feature of the north panorama are the "scour marks" in the dunes - caused by debris blasted away from the crater?

This is another indication of the very young age of Concepcion.

In your north-looking Navcam Pan, notice the new longitudinal dunes (ie, running perpendicular to the ripples) resulting from the additional sand created by the weathering of the impact ejecta.

Many tasty targets in the Loboc area.

--Bill

Image of those tasty treats at the Lompoc site. Oh my, where to start...

Bill, your "longitudinal dunes" of reply 274 are my "scour marks" of reply 273.

I call them "scour marks" because the crests of the dunes are broken by the scour marks and the sides are scraped mostly on the side facing the crater.

In several places I beieve I can see the small rocks that caused the scour marks.

Horton, Bill Harris, the"longitudinal dunes" or "scour marks" I take to be the familiar "cross ripples" oriented NE to SW. These are believed by the mainstream of Mars science to be transverse ripples that have formed in a more recent prevailing wind regime than that which created the larger N S trending ripples.

This discussion has made me think of another mystery: The near ejecta field of Beagle Crater has NE trending cross-ripples that are far larger than average compared with the others we have seen at Meridiani:

I wonder why they are better developed at Beagle than at other places Oppy has visited? Smaller cross-ripples are ubiquitous all along the traverse. I'm puzzled about why, with all the area available for cross-ripples to form big ones are so rare. Maybe the presence of bigger N S ripples prevents big cross-ripples from forming by capturing most of the available particles in their crests. The "ends" of the big ripples, where they taper down to nothing, are routinely bent around into a NE trend suggesting that the later wind regime is still adding material to the big ripples, but without reorienting them fundamentally. Still there are plenty of places with no big older ripples to interfere. Why haven't larger cross-ripples formed in more of the area not covered by big N S ripples?

The big cross-ripples at Beagle, seen above, seem to be built on a base of rocks or have formed between rocks. I don't think that they have ever moved. They have grown and likely changed shape but they do not move downwind. Whatever these are I think that the deposition that creates them is preferentially added to the higher areas of the landscape. If they are newer than the big ripples and have formed in the present climate are they fundamentally different than the big ripples or just younger?

Hort said:

"I call them "scour marks" because the crests of the dunes are broken by the scour marks and the sides are scraped mostly on the side facing the crater."

Those technically aren't scour marks. Scour marks are seabed/lake features caused by dragging ice or erosional features caused by moving water on a streambed. It's be a stretch to apply them to aeolian features. I do see some "deflation pits" caued by debris disrupting the b'berry armor on the dunes; the look like muted craters. The transverse dunes, caused by additional sand an fine material on the surface are perpendicular to the regional ripples and trend E-W-ish.

The linked polar projection of a Sol-2138 Navcam pan shows these features well.

http://www.unmannedspaceflight.com/index.php?act=attach&type=post&id=20532

--Bill

Bill Harris. The availability of powdered debris from the impact and subsequent erosion of the ejecta would provide sufficient dust raw material for the unconsolidated transverse dunes. But while formed later than the armoured dunes these also seem frozen.

I'm not sure that the transverse dunes are frozen. I think that the aeolian processes here are more dynamic than some give them credit for. To be sure, on Mars weathering erosion and transportation happens at a much slower rate than on Earth because of temperature, water and energy considerations, but certainly more rapidly than millenium timescales.

Juicy Pancams, with $%#@*! transmission dropouts. Sigh.

But, many Navcams. Look at how friable (frangible?) the weatherinf rock fragments are, and (hopefully) how the IDD is poised to do the handlens and streakplate routine.

--Bill