Temperature and pressure at Gale, Suitable (for short periods) for liquid water? Options

[Seryddwr]

Just a quick query from someone with no background in science. Obviously, MSL has AFAIK not returned evidence of recent (i.e. years/decades) liquid water in its vicinity; however, I was interested by the following graphs:

08.21.2012: First Pressure Readings on Mars

http://mars.jpl.nasa.gov/msl/multimedia/images/?ImageID=4501

08.21.2012: Taking Mars' Temperature

http://mars.jpl.nasa.gov/msl/multimedia/images/?ImageID=4502

The first indicates that the pressure between 15 Aug and 18 Aug never dropped below c. 690 millibars; the second shows that, for a period of a couple of hours on 16 Aug, the temperature rose above freezing. If water had been present on the surface, then, would it have been liquid during this brief period? The pressure and temperature seemed to satisfy the conditions for liquid water as I understand them (indeed, the pressure seems to be high enough (just) on a 24-hour basis to allow for the presence of liquid water). Thanks in advance for your opinions (corroborative or not!) on this.

[djellison]

It would boil, would it not?

[Eyesonmars]

It would boil, would it not?

As shown in one of my previous post, the surface pressure may be as high as 14mb. At that latitude (40 south) on mars at that season mid day near surface air temperatures are well above freezing. So temperature and pressure are high enough. Rapid evaporative cooling could ice over our glass of ice water in the extreme dryness, even with air temps above freezing. But solar radiation might offset the evaporative cooling. If this happens, our glass of ice water might slowly warm a few degrees before it completely evaporates but because the boiling point might be as high as 10c at 14mb the water would evaporate before it ever warmed to the boiling point.
Like I said, it is a fun little thought experiment. Small changes in parameters drastically change the outcome. For instance, if the glass was sitting on black sand dunes (albedo .05) the infrared warmth ( dune temp could easily be 35-40c) might warm the ice water quickly enough for it to begin boiling before it completely evaporates

[udolein]

For instance, if the glass was sitting on black sand dunes (albedo .05) the infrared warmth ( dune temp could easily be 35-40c) might warm the ice water quickly enough for it to begin boiling before it completely evaporates

The phase transition under the conditions mentioned would happen directly from ice to gas. It evaporates. There would be no boiling at all. At 40c a liquid phase is impossible at 6-10 mbar air pressure.
In my above phase diagram the phase transition would happen from point D to F. No liquid phase at all.

Udo

[Eyesonmars]

The phase transition under the conditions mentioned would happen directly from ice to gas. It evaporates. There would be no boiling at all. At 40c a liquid phase is impossible at 6-10 mbar air pressure.
In my above phase diagram the phase transition would happen from point D to F. No liquid phase at all.

Udo

Note that I am talking about magically placing a glass of ice water ( temp 1c or so) on the surface. Please see earlier post.
As I state, the 40c temp I mentioned is the temp of the sand, not the water. Radiative heating from the surrounding sand would probably be more important than conduction thru the bottom of our glass.

And I'm not clear on why you are referring to the phase diagram of CO2 in some of your post

[Juramike]

Note that I am talking about magically placing a glass of ice water ( temp 1c or so) on the surface.

Or take a glass of ice water and put it in a vacuum chamber and suddenly expose it to vacuum. [Done the equivalent lotsa times in a rotary evaporator].

Doug's right, it would boil. Bubbles of water vapor would form at imperfections in the glass of the surface and it would bloop up out of the glass and go everywhere. A combination of sudden cooling due to more evaporative surface area would make all the flung water droplets quickly turn to ice, which would then sublimate away.

[When this happens in the lab, it is due to the receiver trap bumping, and there is usually a "Dangit!" if any of the water drops land back in the previously dried compound].

(Water-->bloop--->freeze--------------------->sublimate)

The water-bloop-droplet-freeze sequence would happen on the order of a few seconds. If the glass has a rougher surface, it would foam and froth smoothly due to all the nucleation sites. If it was a really smooth surface, it would sit quietly for a second and then just release it in a massive spasm of boiling due to the fewer nucleation sites.