QUOTE (Drkskywxlt @ Apr 22 2011, 09:53 AM)
Perhaps...does the salt in the water also allow it to stay liquid at low pressures as it lowers the freezing point? For pure water that's certainly true.
I think adding salts decreases the vapor pressure of pure water, which increases its boiling temperature. The water boils when its vapor pressure exceeds atmospheric pressure. So, briny liquids should also be more stable at higher elevations on Mars than pure water, all else being equal. Still, I’d expect the stability field of the same liquid to be wider at lower elevations, making its presence more likely in the low elevation north than the south. Aslo the presence of abundant water ice is better documented for the north polar region.
As an additional note, the authors’ Fig. 2 is from images taken in the southern spring (Ls 210°–220°) when the seasonal CO2 cap is rapidly sublimating. I think CO2 can interfere with the spectral signature of water. (It’s interesting that CO2 ice is not included in their Fig. 1 for comparison.)
All in all, based on this layman’s opinion, McEwen is right to be skeptical.