Dark ground images.
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by
battwatch
What is everyones opinion of this image type?
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Kitharode
moderator
In my opinion it's no good asking Kitharode. He's hopeless at these types of backgrounds. Only my opinion of course. 😉
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wassock
moderator
I think it is a late season image the bright bits in the spiders (channels/veins) being the tail end of the melting ice
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jshoe
in response to battwatch's comment.
In my opinion this looks like a great example of the sun's effects on ice deposition and it's illumination afterwards, and, ultimately, in channel development. Channels running from 7:00 to 1:00 are strongly lit by sun from lower right, probably leading to the exchange of extra amounts of CO2 ice, which, in turn, is illuminated more in our viewing direction and looks even brighter than normal. Over the aeons, both effects led to stronger gas flows in the 7:00 to 1:00 channels (compared to those running other directions) which helped create super-highways both wider and straighter than those running perpendicularly. You're looking at those highways and seeing extra white stuff lining the walls. Or, consider this, maybe we just can't see the other channels as well because they are tighter and more convoluted. Do I recall correctly that the "yardangs" which are popular for explaining some of the long straight background textures, often run from the lower left to upper right in the images we receive? If so, this might help explain their formation.
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wassock
moderator
Now we're. Cooking. Not seen that idea before and you have it right regarding the position of the sun. The yardangs are thought to be wind erosion features.
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Kitharode
moderator
in response to jshoe's comment.
Hi jshoe. Good to see you here. I like your description of the image and it certainly makes sense to me. We know from the general discussions that sunlight is a major player in what goes on in these parts, so I think you're pretty much on the money with your description of what's going on in the image.
However, I'm not too sure about the processes being ultimately responsible, over aeons, for channel formation. We haven't nailed down a growth rate for the spider channels yet, but we know from Anya (scientist) that the growth rate is very small. If memory serves, we should think in terms of 'a few mm per martian year at most'. (I'll try and find more on this).
When dealing with astronomical timescales, my feelings are that changes in the axial tilt of Mars (~10-60 deg over 140,000 yrs) and its precession cycle of ~171,000 yrs will alter the balance of power between solar radiation and other channel-forming processes. Currently the south pole of Mars faces the Sun at perihelion (closest to Sun) but in about 85,000 yrs it will face away from the Sun at perihelion. Obviously, before that, neither pole will face the Sun at perihelion. Also obviously, an axial tilt of 60 deg rather than the 25(ish) of today will also cause significant change.
Having said that, I might well be wrong - It wouldn't be the first time. * 😃 *
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JellyMonster
Don't know if this helps. Image has been spun 180 plus a few brightness/contrast/colour/unsharp mask edits.
![Image] (https://dl.dropbox.com/s/5nyk8go9n45c5az/R-51434810ea305267e900c804.jpg).
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