Some interesting stuff about liquid water stability on Mars. Derek Sears reported on a simulator that they have to study evaporation rates under Mars surface conditions. Water (at 0 C, buffered by an underlying ice reservoir) is evaporated under either still or windy conditions. Evaporation rate is ~ 1mm/hr for still conditions and 2-3 for ventilated.

The most significant part was that a film of ice formed within a bout 5 mins and after that, sublimation occurred from the top of the ice which gradually froze down into the liquid.

So you can transiently have liquid water on Mars, if you put it there, but it doesn’t last long in small quantities.

(Note that this doesn’t yet address issues of whether morning frosts can melt before they sublime – that’s for the next round of experiments)