Looks like your hypothesis Dr. Hoffman, is still a hypothesis. The issue of water and life on Mars may be soon resolved in January of 2004 when the Beagle 2 lander and the twin NASA MER Rovers do their work. Get that publicity while you can! Still though, though I think you are wrong in your assessment about liquid CO2 carving out the channels of Mars and causing the gully phenomenon, since the Mars Odyssey gamma spectrometer favors massive amounts of water (H2O ice is still water) the possibility of Martian life has to be considered. Yet, you have come up with an interesting hypothesis that may lend itself to studying other celestial objects such as Kuiper belt objects where the temperature is not above the triple point of water - like Mars can be for extened periods in the equatorial and other regions during the summer season.

Also, how does this recent story about Mars Odyssey fit in with your hypothesis about liquid CO2 flows on Mars?

http://planetary.org/html/news/articlearchive/headlines/2002/wet_mars.html

The research conducted by Krasnapolsky et al is interesting too:

http://www.gsfc.nasa.gov/topstory/20011129marswet.html

MARS WAS ONCE ALL WET

Although covered by frozen deserts today, Mars could have been born with more water in proportion to its mass than the Earth, according to new observations from NASA's Far Ultraviolet Spectroscopic Explorer (FUSE) spacecraft.

The new research is the first detection of molecular hydrogen (H2) in the upper atmosphere of Mars. Molecular hydrogen, which consists of two hydrogen atoms, can be formed from the breakup of water, which is comprised of two hydrogen atoms bound to an oxygen atom (H2O).

With the result, Dr. Vladimir Krasnopolsky of the Catholic University of America, Washington, D.C., and Dr. Paul Feldman of the Johns Hopkins University, Baltimore, MD, were able to derive the quantity of Martian water lost to space and estimate the amount of water Mars had shortly after its formation.

"Our result is an important clue to reconstruct the history of Martian water, because with it and other results, we can estimate the volume of primordial Martian oceans," said Krasnopolsky, who is lead author of a paper on the research to be published in the journal Science November 30. "We calculate that if the initial quantity of water on Mars could have been evenly distributed across the planet somehow, it would have been equivalent to a global Martian ocean at least three-quarters of a mile (1.25 kilometers) deep. This is 1.3 times more water per mass than the Earth." An ancient ocean could have covered most of the northern hemisphere of Mars, which is a vast basin according to a topographic survey by NASA's Mars Global Surveyor (MGS) spacecraft.

Scientists Discover 'Recent' Deluge on Mars

http://www.planetary.org/html/news/articlearchive/headlines/2002/MarsFloods-2-27-02.htm