On the Road Again - volume 8 - Page 17

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MPJ


Posts: 250

Reply: 321



PostPosted: May 31, 2011 1:33 PM 

Very nice MI pan of Valdivia in re319 Horton, maybe too much interesting details for a rather stupid robotic explorer Very Happy

hortonheardawho


Posts: 3465

Reply: 322



PostPosted: May 31, 2011 4:14 PM 

sol 2595 ( May 13, 2011 ) right half of saturated false color panorama of crater "Skylab":

The left half still not yet complete.

sol 2612 ( May 30, 2011 ) Port Otway trench:

and "Gumdrop" crater:

Today's plan: more APXS integration.

LWS


Posts: 3062

Reply: 323



PostPosted: May 31, 2011 9:29 PM 

Hi Hort;

Beautiful example of fluid liquid dust carving streams at Port Otway trench.

Winston

Kye Goodwin


Posts: 1166

Reply: 324



PostPosted: May 31, 2011 10:28 PM 

Thanks Horton for your 322, Your panorama of Skylab Crater is a great place to notice the quirky orientation of crested sand-tails, which are very numerous here and generally rare "behind" the many standing rocks of Meridiani. The general rule I've come up with, which I first noticed at Fram Crater, is that tails against rocks in a crater point away from the crater. Outside craters the rule does not apply, so the rule might be more like: tails in craters form uphill from rocks. Overwhelmingly crested sand-tails form in the near vicinity of craters, old and young, large and small, but not all craters, and not out on the plains even where standing rocks are numerous.

Anyway it is easy to see numerous tails in Horton's full resolution panorama of Skylab some that point to the left on the left wall of the crater and some that point to the right on right wall of the crater. That should be enough to make a person think twice about what these are.

Barsoomer


Posts: 344

Reply: 325



PostPosted: May 31, 2011 10:36 PM 

In the Port Otway trench, the sharp boundary between trench and berries is very striking. Almost like a waterline.

Barsoomer


Posts: 344

Reply: 326



PostPosted: June 1, 2011 11:04 AM 

Bottom, center right: indentations that look like tiny ripples.

Ben


Posts: 5

Reply: 327



PostPosted: June 1, 2011 1:27 PM 

One thing about this forum is that WE all quickly examine Hort's excellent images searching for something that supports our own agenda. Smile

What can I find that would indicate air-fall deposition . Razz

hortonheardawho


Posts: 3465

Reply: 328



PostPosted: June 1, 2011 2:03 PM 

sol 2561 ( Apr 8, 2011 ) drive animation:

I think this is the longest drive sequence yet done by Oppy. Some interesting trench crossing.

Speaking of driving, today sol 2614 is a drive day.

And here is an interesting sol 2584 ( May 2, 2011 ) 360 degree panorama near the Mercury program craters.

Lots and lots of craters of different types.

You can follow the rover tracks back to Santa Maria crater on the horizon.

Ben


Posts: 5

Reply: 329



PostPosted: June 1, 2011 4:11 PM 

Lots of bifurcating fractures (joints) ahead, even one that crosses a small crater to the SE.
Makes one wonder if we are approaching a lower part of the section that is exposing an older joint system.
The presence of these in the subsurface behind us might explain the void space where we saw dust collapsed into cracks

hortonheardawho


Posts: 3465

Reply: 330



PostPosted: June 2, 2011 8:35 AM 

sol 2614 ( Jun 2, 2011 ) L0 2x1 in next drive direction:

Ah. The 20 meter crater that Oppy is now near is not "Young Blocky" - but the 20 meter crater about 200 meters east is.

The drive index changed from BA00 to BAQI for a guestimated drive of 138 meters.

Barsoomer


Posts: 344

Reply: 331



PostPosted: June 2, 2011 10:57 AM 

Question: When the ripples move, do the berries get carried along with them, or do the berries stay behind?

Fred


Posts: 73

Reply: 332



PostPosted: June 2, 2011 12:30 PM 

Barsoomer wrote:

Question: When the ripples move, do the berries get carried along with them, or do the berries stay behind?

Priceless!!

Concerning the white fibrous material: The last I saw it was in the crater not on the edge so no correlation.

Ben


Posts: 5

Reply: 333



PostPosted: June 2, 2011 1:16 PM 

I am puzzled by Gumdrop crater and don't want to be redundant but where is the ejecta?
The sand around the rim doesn't appear to be thick enough to cover it . As Hort says a lot of splainin needed. Confused

hortonheardawho


Posts: 3465

Reply: 334



PostPosted: June 2, 2011 2:00 PM 

Ben, I have always suspected that the "dune craters" ( like Gumdrop ) are sand sinkholes caused by sand draining into subsurface cavities - perhaps caused by sublimated blocks of ice?

mann


Posts: 161

Reply: 335



PostPosted: June 2, 2011 2:51 PM 

I am thinking along the same lines as Horton, except that some of these craters look more like "kettle holes".

Kye Goodwin


Posts: 1166

Reply: 336



PostPosted: June 2, 2011 4:53 PM 

Ben, re your 333, I'm encouraged by your puzzlement over Gumdrop Crater, which I share, and I have no answers to alleviate it. We have no idea how erosion works on Mars, so we really don't know what older craters should look like, or even which are the older ones among the Mercury Program craters, if they're not all the same age. If sand and granules move in the wind I'd expect all the smaller craters to be full of sand and granules on top of a lining of breccia which should have originally covered the floor and walls. Instead, much of the breccia seems to have eroded away FROM THE CRATER INTERIORS FIRST leaving lots of bedrock showing as at Endurance, Beagle, Victoria and Santa Maria while there is still ejecta on the rims. My guess is that some of the craters are sites of accelerated chemical erosion, and sand and granules do not move in the wind.

Horton, re your 334, Thanks for the binocular pair of images of Gumdrop Crater (reply 322), but the 3D information it provides sure makes it look like Gumdrop isn't a "dune crater", but instead must extend well down into the bright rock.

Barsoomer, re your 331, No one knows how the ripples move, or even IF they move, really. Lately we have seen a lot of evidence that many of these ripples east of Santa Maria are situated on top of ridges in the bright rock. Maybe these ripples don't move at all, or maybe they move so slowly or infrequently that the bright rock can erode significantly in the inter-ripples while they are exposed. It is part of the mainstream view that the rock erodes faster than the ripples and that the north-south ripples last were active between 100,000 and 300,00 years ago:

http://www.lpi.usra.edu/meetings/lpsc2010/pdf/2373.pdf

Trouble is, if we assume that say 10 cm of bright rock has eroded in the inter-ripples in a quarter million years, to create the ridges we see, then we get a surprisingly fast rate of erosion, amounting to 100's of meters over a billion years.

Kye Goodwin


Posts: 1166

Reply: 337



PostPosted: June 2, 2011 6:28 PM 

It now occurs to me, after my 336, Horton, that there is a sense in which Gumdrop could be called a "dune crater". It is striking how well the surfaces of Gumdrop are integrated into the ripples that surround it. Gumdrop may be "overprinted" on the ripples, but it seems that there has been enough time pass for it to "go native", becoming much like the now tidy surroundings that it must have thoroughly messed up in the impact. The bright rim crests are now much like the bright ripple crests. The surfaces of ripples and crater are both smooth and apparently surfaced with similar particles. I think I see some indication of breccia and a raised rim, but it is low and mostly covered with soil, soil that has been smoothed and "armoured" with granules and pebbles in the same way as the ripple surfaces.

Gumdrop is so circular that it must postdate the last "episode" of ripple movement, and yet during that time it has been beautifully integrated into the scene, apparently by processes that do not move the ripples but rapidly erode the bright rock. Hmmm?

Ben


Posts: 5

Reply: 338



PostPosted: June 2, 2011 6:46 PM 

Kye; I don't think we can assume anything is constant (like erosion)and suspect there were long periods one practically nothing happened.

I think what Hort was attempting to say is that the bedrock surface collapsed into the sink hole as well as later sand percolation.

Barsoomer


Posts: 344

Reply: 339



PostPosted: June 2, 2011 7:56 PM 

The paper about the Meridiani meteorites said that berries were delivered onto one of the meteorites (I think block island) by movement of the ripples.

I'm wondering how the ripples would get under the berries in the first place. Why wouldn't ripple movement just roll over the berries and cover them with sand?

Ben


Posts: 5

Reply: 340



PostPosted: June 2, 2011 11:13 PM 

Barsoomer; My perception of the berry-ripple relationship is that the berries represent a lag feature that moves very little and the ripples migrate over them as you point out.

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