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Spring at Cape York, Sol 2947 (after Greeley Haven) - sol 3040
stewjack
post Jun 21 2012, 09:46 PM
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QUOTE (fredk @ Jun 21 2012, 03:38 PM) *
That looks about right.

Thanks fredk. My track record of matching low-relief terrains is very poor. However, that match looked to-good-to-be-true.

Jack
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Tesheiner
post Jun 22 2012, 06:53 AM
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Here's the navcam mosaic.

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Stu
post Jun 22 2012, 12:25 PM
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Shattered/cracked rocks at Oppy's 'feet'...

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algorimancer
post Jun 22 2012, 01:11 PM
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QUOTE (Tesheiner @ Jun 22 2012, 12:53 AM) *
...mosaic.

Now that the "Wedge" (aka several other names) is clearly within reach, I find myself wondering: how would we distinguish between a small fluvial gully (unlikely) and a fracture-based gully (likely), much less a fluvial feature which happened to flow through an existing fracture? The obvious distinguishing characteristics of a fluvial feature on at this scale, the flow-shaped sand and silt on the floor, would have long ago been wind-eroded and partially buried by dust and dunes over time, and water-smoothing of rocks in unlikely if water flowed only briefly. It seems to me that the null hypothesis would be to assume it is fracture-based, and the only way to rule it out would be if a cross-section of the floor sediment happened to be exposed, perhaps by a small crater or intersecting fracture, and clearly fluvial-derived layering were visible. At this point, Occam's Razor has me firmly convinced that it's a fracture feature, but it would be interesting to learn otherwise.
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john_s
post Jun 22 2012, 02:16 PM
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i wouldn't be surprised if the "wedge" turns out not to be a gully or depression at all...

John
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marsophile
post Jun 22 2012, 03:03 PM
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If there is a continuation of a shallow depression up into the hills (possible in the HIRISE image), that might be a piece of evidence suggesting a filled-in gully.
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Phil Stooke
post Jun 22 2012, 05:22 PM
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I think that, to be realistic about geomorphological processes in an area like this, with plenty of evidence of erosion since Noachian times (see Golombek's recent paper on crater ages in Meridiani, saying basically all Hesperian craters are completely eroded away, Erebus etc. are Noachian), a Noachian gully on this scale would not have survived. Filling it with debris and exhuming it recently is too ad hoc. A fracture induced by the impact forming the crater Antares just to the north, or a gouge created by its ejecta, is much more likely.

Phil



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CosmicRocker
post Jun 23 2012, 06:07 AM
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It seems likely to me that this notch is a relatively recent feature created by aeolian erosion along a zone of weakness such as a fracture. By recent, I mean tens of thousands of years to perhaps a few million years old at the most. I hope we'll get a close enough look at it to see if fracturing is involved.

At the very northern tip of Cape York is an almost insignificant geomorphic feature that I have been calling the mini-Notch. It looks like a minor, wind-eroded gully that is oriented in roughly the same NE/SW direction as the main notch or wedge. This suggests the possibility of an underlying structural "grain" that could be controlling the orientation of zones or planes of weakness in the bedrock. We already know that the rock is fractured because the calcite veins appear to be fracture fillings. However, I haven't noticed many of the calcite veins oriented in the same direction as the notch.

We seem to be heading in the general direction of this mini-notch. It's only about 120 feet to the ENE, so perhaps Oppy will slow down for a few pics if she passes by. wink.gif
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fredk
post Jun 23 2012, 02:55 PM
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I've been eyeing that mininotch too, Rocker...

Great news in the latest update:
QUOTE
The rover continues to benefit from solar array dust cleaning events, which have greatly increased the daily energy production. As of Sol 2989 (June 20, 2012), solar array energy production was 526 watt-hours with a lower atmospheric opacity (Tau) of 0.229 and an improved solar array dust factor of 0.684.
That's just what we need for: wheel.gif wheel.gif wheel.gif smile.gif
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ngunn
post Jun 23 2012, 03:55 PM
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There seems to be an inner and an outer bench at this part of Cape York. I'd expect them to continue northward to look at the edge of the outer one before heading SE towards both notches.
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Stu
post Jun 23 2012, 09:14 PM
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Couple of MI frames came back... tried my best to make something out of them...

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Guest_Sunspot_*
post Jun 24 2012, 12:09 PM
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QUOTE (john_s @ Jun 22 2012, 03:16 PM) *
i wouldn't be surprised if the "wedge" turns out not to be a gully or depression at all...

John


I don't think it is either.

If you look at the "bath tub ring" around Cape York, from HiRISE you get the impression that there is a small vertical "step" like feature surrounding the Cape, but images from Opportunity show no such thing. I think the Gully is probably just a"slice" out of the white outcrop with no vertical relief at all. probably unsure.gif
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Stu
post Jun 24 2012, 12:36 PM
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Well that peed on our chips, didn't it?


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fredk
post Jun 24 2012, 02:46 PM
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Don't give up hope yet, Stu! I think there is some relief. Remember when we first made landfall on CY almost a year ago, there was a bit of a step up - check out the vertical stretch in this post.

We had a good look at Whim Creek (the wedge/notch) on 2917. The sun was low in the west and it really looks to me like the far side of Whim Creek is sloped towards the west since it's very bright (arrowed feature):
Attached Image

So I'm betting for some relief, but nothing too dramatic - this is Meridiani, after all!
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CosmicRocker
post Jun 25 2012, 04:36 AM
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There is undoubtedly some relief at the notch, but I would have to agree that there is less relief than we were expecting when Cape York was first announced as Opportunity's next goal after Victoria.

Of course, none of us were surprised by Cape York's lack of relief, either. wink.gif


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