Below are some miscellaneous followups to some posts in the thread "water flow 68 degrees south on Mars":

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In response to Robert's post at:
http://www.habitablezone.com/space/messages/13121.html

Robert wrote:
"My algorithm works on simple column averages. MSSS has a more advanced destreaking algorithm that's based on the derivative of column-to-column variation--it acts as a high-pass filter. "

Alex writes:
There are many MOC destriping algorithms in use at various sites and by various people. The one MSSS uses for systematic processing simply applies multiplicative coefficients, derived from ground and flight flat fields, to each pixel. It is not, in any meaning of the term, a high-pass filter, since it processes each pixel independently of its neighbors. The processing MSSS applies to the image archive is simply a destripe followed by an auto-ends contrast enhancement (and, if the image is map-projected, an image warp.) While there is some filtering implicit in the pixel interpolation used in the warp (low pass, if anything) MSSS applies no explicit filtration of any kind to the image archive. Obviously, the raw data is raw and has not been processed in any way. For the captioned releases, of course, some manipulations are often done, usually in Photoshop, to enhance the images. If one doubts MSSS'
scientific integrity there, feel free to go back to the raw images.

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In response to Robert's post at:
http://www.habitablezone.com/space/messages/13089.html

Robert wrote:
HH Kiefer at USGS/Flagstaff would probably agree with you. He wrote a paper for Mars Polar Science 2000 titled "Annual Punctuated CO2 Slab-Ice and Jets on Mars". I have a copy of the abstract but I can't find a link to the conference site for the full paper.

Alex writes:
See
Kieffer, H.H., Annual punctuated CO2 slab-ice and jets on Mars, 2nd
International Conference on Mars Polar Science and Exploration,
Reykjavik, Abstract #4095, (2000).
http://www.lpi.usra.edu/meetings/polar2000/pdf/4095.pdf

Robert wrote:
In case you were wondering where Greg got the term "Martian spiders", Kiefer mentions that that's the moniker the MOC team gave these features when they first spotted them. Morphology, not a hint of biology....

Alex writes:
True, though in all honesty many of the features Greg points to bear little or no resemblance to the "spiders" that Kieffer presented at the Reykjavik conference, which I had the good fortune to attend. The "gullies" depicted in MOC NA M09-05128 were obviously formed by a fluid or fluidized debris moving downslope in response to the gravity gradient, which is typified by anastomosis, channel piracy, V-shaped cross sections, etc. In contrast, Kieffer's "spiders" are usually not found on slopes, and are posited to represent subsurface gas channels serving as conduits for CO2 jets, which may be visible through transparent sections of martian ice. Dust entrained in the flow may be deposited (and shaped by aeolian processes) on the surface when the CO2 breaches through. Unclear, though, are the mechanics for this model. At first glance it would appear that if the separate channels were interconnected, a breach would depressurize the entire system. At any rate, for an example of what Keiffer is actually referring to see:

Lovett, R.A., 'Spiders' Channel Mars Polar Ice Cap, Science 289, 1853
(2000).

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In response to Greg's post at:
http://www.habitablezone.com/space/messages/13108.html

Greg wrote:
The links below appear to show that temperatures at 65 degrees latitude hover just above zero for 2 months or more. Add to this that dark soil will get hotter and salts can make water stay liquid down to 50 degrees below zero and the idea of water outflows is perhaps not so far fetched.

Alex writes:
Perhaps, perhaps not. A couple of points should be made. The gullies in M09-05128, like the majority of the Malin and Edgett examples, are on the pole facing slope, which is one of coldest types of surfaces on Mars. This is problematic for the plausibility of liquid water vs. alternative erosive agents (e.g. CO2-lubricated density flows), the MGS TES bolometer readings, notwithstanding. However, obliquity excursions, which expose one pole (and the other) to higher solar insolation, are another matter...

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Alex R. Blackwell
University of Hawaii