QUOTE (djellison @ Mar 2 2008, 10:39 AM)
So 'it looks like' then - and to be fair, that's the conclusion Malin et.al. made from MOC imagery as well. No offense, but results of CFD study of HiRISE generated DEM's holds more water (pun intended) at this stage, imho.
"looks like" is powerful evidence it refers to specific complex landforms. How many dry flows do you know of that produce meandering channels, but and fill structures, terraces, lateral channel migration, distributary channels, etc.?
I have not yet read the paper in geology[/i]. I will get to it today. But as far as I can tell it is about a specific fature, not te ones I have indicated. Given the diversity of features called gullies it is unjustified to extend conclusions from a few examples to all. landscapes don't work like that. On Earth we see glullies formed by wet plastic flow, piping collapse, sapping, runoff snownelt, placial melt, spring discharge, dry flow, high density and flow density fluid flows. Many of these are likely on Mars, some are not.
The problem I have with the water theory is this. Where's it coming from? To be a squiring gun for millions, tens of million, hundreds of millions of years or more - to be doing it for as long as Mars has been as it is today - surely, any such reservoirs would have been exhaust in the significantly geological past. It's a one shot activity. Squirt - boil - evaporate - gone. I don't think we can realistically expect a water cycle to put that volume back into the soil.
Then clearly there has to be some sort of water cycle. At what rates and mechanisms remains to be seen. But we cannot ignore the morphological evidence.
What's going to be most interesting (and I'm surprised we've not seen it yet) is CRISM results of the 'outflow'.
And what will CRISM say? Spectroscoptically a wet flow will look the same as a dry flow once the water as gone. It is a very limited tool for understanding landforms as very few landforms are conclusvely linked to specific mineraology, and almost all landforms can be found in materials of a wide range of composition.