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Re: My bet on what this is likely to be:
Posted by Robert (64.79.10.252) on 8/6/2001 8:11:57 PM
In Reply to: My bet on what this is likely to be: posted by ebnelson on 8/6/2001 5:46:24 PM

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.
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....

--Robert
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The link Robert gives for the abstract is:

http://www.marscentral.com/science/mps2000/MPS2000_4095_Annual_CO2_Slab-Ice_Jets.pdf

I think this is the full report given at the conference. It looks like it's incomplete because some references are missing.

In any case the authors propose the spiders are due to CO2 gas sublimating in channelized flow. Note if this is an accurate representation of their origin then this could support Nick Hoffmans's contention that the channels seen in general on Mars could have been carved by CO2 gas.
A key complaint against Hoffman's argument was the dendritic patterns seen in some channels. However, such dendritic patterns are seen in the spiders as well. To apply the explanation to the channels seen even in equatorial regions, you would have to suppose they were covered at some point by ice.
The dendritic patterns can be seen on Greg Orme's page of the spiders:

http://www.martianspiders.com/

However, the very fact that such dendritic patterns are seen should suggest they are indeed formed by flowing water. Current opinion largely points to the idea that the south polar cap consists largely of water with a CO2 covering. In some locations the water may be in liquid form because of the overpressure of the CO2 ice.
One notes the spiders in some case are on raised pedestals. One is reminded of pingo-like structures seen in arctic regions. I seem to recall seeing in such structures streams cut into the top of the structures. Then the processes which force water up to the top of these pedestals may also be operating on Mars to form the spiders seen.

Bob Clark