Farewell Beacon..., The next cape beckons... Options

[Phil Stooke]

I looked back, but I don't see that at Bonneville. From orbit, nothing looks like it's blowing out. From the rim, the dark streaks crossing Bonnevile look like dust devil tracks to me. The one area that might be different is an area of dark dunes under the west wall, but other dunes are lighter, suggesting to me another DD track, or possibly a patch of dark sand like Eldorado, which we do see getting trapped in certain topographic situations.

Phil

[MarkL]

Good one Shaka. Much rather be a dirty streaker!

I might go for a clean streak though, if the special mechanism that makes it appear as though dust is coming out of the bays is explained by repeated cleaning events. Well behaved dust devils perhaps? Also, in Meridiani the dust is dark and the outcrops are light, unlike much of the rest of Mars.

Prometheus, that's it!

[dvandorn]

I really have to think Phil is right, that the dark areas have been windswept "clean" of the ubiquitous bright dust. Which means that Oppy ought to be able to get a nice panel-cleaning by placing herself in the path of those winds!

-the other Doug

[CosmicRocker]

... But Tom, those of us in the "Ancient Victoria" school of thought, don't believe that we are seeing, driving over, or ratting Victoria's ejecta. We hold that ejecta is nowhere to be seen. What we are seeing is sandstone that roofed over Victoria back in the Noachian/Hesperian, was subsequently indurated and leached by ground water to produce concretions, and finally eroded and collapsed.

I am frantically awaiting close-up views of the uppermost exposures in the capes to see if they are primarily intact, in situ, more or less horizontal sandstones. The latest pancam of "Hoy" looks remarkably in situ right to the top. If close examination confirms this all around Vikky, then I will hold my hypothesis to be supported. I cannot emphasize too strongly that a hypervelocity impact shatters the target rocks near the crater, transforms some into exotic forms, hurls them high into the air and deposits them around the crater with a more or less random orientation of chunks (OK, clasts) in an impact breccia. We saw some of this around Beagle, though that was such a tiny crater that regular impact models may apply imperfectly.
I have not yet seen anything around Victoria that I would call impact breccia. Close-up views may reveal it, if we ever get any. Hence my disappointment when Beacon was bypassed. ...

But Shaka, I contend that we have seen several cross sections of capes relatively close-up at this point, including CSM. All of them appeared to be mantled by a jumbled layer of blocks in random orientations. That looks like an impact breccia to me. The stable places that have endured long periods of erosion seem to display flat faces eroded by wind, and the less stable areas that have seen mass wasting more recently display the boulders in various stages of erosion. I don't see anything like in-place bedding at the surface on any of the capes, so far.

I know that in the past I had argued that Victoria wasn't all that ancient, but I have since modified my view and have mentioned that. I think it is fairly old, but I am not certain how old. I am still looking for evidence of the hypothesized ancient fill that was eroded, undercut, and which subsequently collapsed. I am not convinced I see it in the close-ups we have so far. If I had to make a guess from our current selection of close-up samples, I'd guess the original crater was smaller than the current hole.

I agree with Phil's points. I think our position represents one pole of a "streak hypothesis", ...
We could call these two schools of thought, the "Clean Streakers" and the "Dirty Streakers"!
I'm sure Ustrax could devise some appropriate mascots.
Who wants to sign up?

I agree with him too, but...Oh, no. Let's not start another polarizing argument with team badges. We won't have the measurements needed to decide until Opportunity gets to a dark streak, and even then we won't have the calibrated spectral information. From my point of view, the simplest explanation is that the well observed and globally distributed light dust has been removed here, as it has on all of the rougher, upper slopes of this crater...

[ustrax]

We could call these two schools of thought, the "Clean Streakers" and the "Dirty Streakers"!
I'm sure Ustrax could devise some appropriate mascots.
Who wants to sign up?

I hope this leaves clear what is my position about this childish creation of teams to discuss such important subjects...

[Marz]

I hope this leaves clear what is my position about this childish creation of teams to discuss such important subjects...

I think I just heard Doug breath a deep sigh of relief!

Phil seemed to sum up what I think the streaks are, so I suppose I'm more of a clean-streaker. That seems alot more comfy than being a fence-sitting streaker...

[MizarKey]

I'm joining the 'clean' streakers. But Oppy should be careful approaching the cleaned area, there may be dust buildup surrounding the cleaned areas.

I wonder if the winds that create the cleaned streaks are seasonal or persistent?

[Jeff7]

El Dorado was a dark spot though, and it was a prime deposition spot.


Either way, I imagine we'll find out soon enough what's going on at those streaks.

[MarkL]

I hope this leaves clear what is my position about this childish creation of teams to discuss such important subjects...

I am so on that bandwagon Ustrax!

[sattrackpro]

I'm joining the 'clean' streakers. But Oppy should be careful approaching the cleaned area, there may be dust buildup surrounding the cleaned areas.

I wonder if the winds that create the cleaned streaks are seasonal or persistent?

As with Spirit's local where winds develop in the summer, I'd expect similar seasonal effects at Victoria too.

Since the wind 'tracks' are relatively short (and wider) by comparison to many seen at craters in Gusev, it appears that the size and strength of the whirlwinds that form in Vicky's bowl are probably shorter-termed, somewhat weaker, and less tightly concentrated than those observed at Gusev.

[fredk]

Not a long drive sol 1012 but enough to give a nice long baseline with the 1009 images in the direction of the Hoy cliff feature. This makes it a lot easier to make out where one cape ends and the next one farther back begins in the images:

I prefer the cross-eyed version:

Some distortion here since movement wasn't perpendicular to the line of sight, and pretty serious lighting differences.

[exoplanet]

I'm beginning to think that Victoria with its "capes and bays" looks more and more like a sinkhole rather than a crater.

See here:

http://ga.water.usgs.gov/edu/earthgwsinkholes.html

The first image at the above link looks nearly identical to the "bays" that we see in Victoria.

[alan]

I'm joining the 'clean' streakers. But Oppy should be careful approaching the cleaned area, there may be dust buildup surrounding the cleaned areas.

I'm not worried about dust build up on Oppy. Compared to Spirit she seems to have better luck finding cleaning events. Compare the sundials of the two rovers.

[ngunn]

I'm beginning to think that Victoria with its "capes and bays" looks more and more like a sinkhole rather than a crater.

I think it's a bit of both: Impact - fluidisation of substratum - undermining and irregular collapse of rim - wasting by sublimation from the fluidised floor material - partial infill and some reshaping of rim by aeolian processes. This is an old idea and we have seen much since it was first aired (2004 if not before), including the paper on the burial and exhumation theory in print, another paper on a possible new easy-melt Martian mineral, HiRise and all the Rover imagery so far. I haven't seen anything yet that makes me want to switch my bet.

[jvandriel]

The panoramic view in the drive direction on Sol 1012.

Taken with the L0 Navcam.

jvandriel

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