On the Road Again - volume 3 - Page 7

sol 2051 L7R12 detail of another half meter block:

with links to my "best guess" of the map location.

The crater on the horizon is about 500 meters distant.

I used the angle between the crater and the block plus the pancam triangulation distance to locate the block's approximate location and then selected the brightest, smallest area of pixels ( assuming the block is very bright ) to fix the block position on the map.

Sorry for the delay.

Serpens said in reply 76:
I think I will stick with schreibersite and an acidic water table. I don't follow the humidity comment unless this was a few billion years in the past.

Humidity reaches 100 % every night on Mars. The thermal bottom is reached by water saturation point or it would get even colder. The ground acts as a condensation point and forms frost. When, probably every night.

How much frost is around when the warm sun rises is unknown but we know it is there. Being that the meteorite rest on the ground it is close to the moisture and micro-climate that forms however fleeting.
Billions of years ago? Not a chance brother. Do not quit your day job.

Fred

sol 2051 ( Oct 31, 2009 ) R12 4x1 in next drive direction:

Today ( sol 2054 ) is a driving day. There should have a better view of the 1/2 meter block in reply 121.

And here is the sol 2047 R0 7x1 view of the "fresh" crater "Trinidad".

Eight L257R2 images were taken of Trinidad. Hopefully "someday" they will be downlinked, as there seems to be some interesting rocks scattered about.

Based on wind erosion of some of the ejecta and the craters influence on adjacent ripples, I would say that it is not too recent and most likely during the ripple formation process.

Here's a new paper about the cobbles:

http://meetingorganizer.copernicus.org/EPSC2009/EPSC2009-512.pdf

It answers a question that I have had for a long time: Aside from the meteorite group what sort of material are MOST of the cobbles? These authors find a composition for the most numerous Arkansas group of cobbles that is intermediate between the bright sulphate-rich bedrock and a basaltic component. They propose that the brecciated textures imaged with the MI suggest impact mixing of the bright outcrop rock with fused basaltic soil or other basaltic inputs.

Another category includes a growing number of stony-iron meteorite candidates.

If a few separate cobbles were studied from one of these big "piles" of cobbles, and the sample included just one - or more than one of the types of cobbles, that might tell something about how the cobble material has been transported.

sol 2047 L0R0 detail of Trinidad ejecta on the dune ripples:

Always best to look at this stuff in 3D.

I think the bright, flat rocks on the surface of the ripples are bright, flat ejecta thrown on the dune - not eroded in place.

My guess is still that Trinidad crater was created after the dunes.

Am I to understand that they are implying that the cobbles are highly transformed erosional remnants, from both basaltic Martian secondary impact ejecta material hurled from very great distances, as well as various impactor material altered and reacted with the evaporite stuff?

Hortonheardawho.

I think you are right - for what little my endorsement is worth. But given the weathering of the ejecta this means that the dunes are very very old.

sol 2054 ( Nov 3, 2009 )R12 4x1 pan in next drive direction after 73 meter backwards drive south:

With links to the map location and 3D of the block now 85 meters distant.

If you look at the detail 3D of the block I think you can see a smaller block to the left that is most likely a meteorite.

Today is a driving day ( sol 2055 ) and we will get our first close views of Marquette Island - the block in reply 121.

While you wait, you may enjoy this sol 2043 ( Oct 23, 2009 ) L257 3x1 false color panorama of the cobble field:

with a link to a 3D close view of the cobbles after the rover drove over them.

Thomas Lee Elifritz, re your reply 127, which may be a response to my reply 125, that paper as I understand it is suggesting that the material in one of the most common types of cobble (the "Arkansas" group) has been mixed and fused together by a large impact explosion. Both of the components appear to be Mars material not primary impactor material. I don't think that the authors attempt to explain exactly how the cobble material came to be where we see it, except that it might have been "moved laterally" by impact, not necessarily the same impact that created it. To me the small local impacts seem an unlikely origin for the cobble material because they would not create enough heat and pressure to fuse new rock. A problem for any theory about transport of the cobble material is to explain how these cobble mounds have been created from stuff that has been moved a great distance. As I see it, either the mound material has traveled as a single large piece and then disintegrated into fragments in the mound locations, or the individual cobbles have been moved by a process that concentrated them together in the mounds.

You refer to ejecta "hurled" from impacts, implying a ballistic sort of tranport, but large Mars impacts very often transport ejecta by a very different process in which the ejecta fluidizes and surges horizontally across the entire surrounding area, often leaving a thicker blanket of material called a rampart along the outside (distal) edge of the ejecta field. For some reason this common Mars process seldom appears in visualizations of Meridiani's past. Most people still think of Mars impacts as dry blasts that spread breccia in rays as on the Moon, but Mars often does it differently. There is extensive rampart crater literature on-line.

Horton, Serpens, re your 126 and 128, I concur. Even Beagle Crater appears to postdate the big north-south ripples, because they are not present on Beagle's ejecta field but some fairly large diagonally oriented cross-ripples have developed there. Victoria has large north-south ripples on her annulus, so Victoria is older than at least some of the north-south ripples.

sol 2055 ( Nov 4, 2009 ) front hazcam L0R0 after 3 meter move:

with link to right front wheel detail.

UH OH.

Looks like Oppy has ventured into a "fluffy" dust drift area. Notice how red the dune is in this view.

Red dune trough means stop. Blue dune trough means go.

Kye Goodwin. Your comment on fluidized flow (reply 131) piqued my interest. But a bit of reading seems to indicate that, as could be expected, ballistic emplacement as well as fluidised runout takes place. I am sure that there are lots of papers and theories around but Martian runout doesn't seem terribly efficient and it is difficult to see how Meridiani could be attributed to fluidised impact surge. There don't seem to be any candidate craters in the vicinity.

serpens, re your 134, I see 4 obvious craters so far that likely contributed material to Oppy's neighborhood if we take 1 crater diameter as the maximum distance of influence, which is fairly conservative: the Northern Lowlands, the Chryse Basin, Endeavor Crater, and the nameless 140 km crater to the southwest. Oppy is just outside the rim of this last one but the crater is wholly buried on Oppy's side. Of course there could be layers and layers of now obscured craters and ejecta fields.

The problem is to see the order of events and discern what event or events contributed the last layers to the surfaces that Oppy has imaged close-up. Not an easy task. I've been pursuing images of the context of Meridiani at different scales. This big paper(slow download maybe) by Kenneth Edgett has a lot of intermediate scale images that fill in some of the blanks for me:

http://marsjournal.org/contents/2005/0002/files/edgett_mars_2005_0002.pdf

Check out the big buried crater page 53, and a possible buried double ring impact structure proposed by Newsom, page 52.

I'm guessing that the 140 km crater to the south-west and Endeavor Crater have both been partially filled by one of the events (possibly Newsom's)that has contributed bedded rock to the MER traverse, so the ejecta of these two craters is probably not on top of the plains where Oppy is.

There was a paper about ejecta runout efficiency in the last LPSC that concluded liquid water is likely involved in the fluidization. I'll try to find it for another post.

sol 2056 ( Nov 5, 2009 ) L256 2x1 of Marquette Island Block:

About 12.5 meters from the 30 cm block now.

Looks like the "slip parameters" were relaxed a bit and the old gal was on her way...

Bottom one third, a little right of center. Near the odd-looking rock, are those scrape marks in the soil? Or just wind channels?

sol 2056 L256R1 detail of Marquette Island Block:

This does not appear to be a meteorite. Looks like a quick snap of this block field and it's westward HO!

Barsoomer, you might want to look at the 3D of this image.

Thank you very much for the link Kye - a very interesting paper. One aspect of Meridiani that I was not around was the presence of inverted channels which indicate significant water flow in the far past. The ancient playa/shallow lake scenario seems more likely now.

The possible double ring crater underlying Meridiani would have occurred well before the formation of the Planum.

Serpens, I don't know what to think of Newsom's ring structure. Edgett is also skeptical. It would be quite possible for some parts of the surge-plain created by a large impact to be preserved after the crater is covered or eroded into obscurity.

I didn't even mention the complication of possible erosion in the puzzle. Edgett sees many meters of erosion in places, and though I am skeptical that there has been much cut away from Oppy's plains, I couldn't rule out the possibility elsewhere around Meridiani. Victoria's bays make 100's of meters of erosion in some places seem quite plausible to me. Minor differences in this weak soluble bedrock could make orders of magnitude differences to how quickly it erodes. Oppy has just found a place where the resistance is high and fairly uniform.

The channels are old news, similar to ones known from many highland locations. People have been interpreting and reinterpreting them for decades. Some of Mars channels are CERTAINLY catastrophic and the rest are weird and possibly catastrophic, never quite making sense as surface runoff channels from a long period of warm-wet climate. Why don't we see any channels associated with the specific putative water-layed sediments that Oppy has imaged? Edgett puts those channels far from the hematite plains stratigraphically.