re: Some 40th LPSC Phoenix abstracts.
Perchlorate salts in the soil doesn't mean that briny liquids are forming. There's a lot of perchlorate, and the air is thin. The soil might be full of 'damp' perchlorate that never gets past the point of becoming brine. Since all the elements are there for perchlorate brines I'm sure it's happened once or twice in the history of these Martian plains, but the right set of circumstances for the salts to absorb enough water vapor to become brine might come together only rarely.