Temperature and pressure at Gale, Suitable (for short periods) for liquid water? |
Temperature and pressure at Gale, Suitable (for short periods) for liquid water? |
Sep 30 2012, 03:23 PM
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#1
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Junior Member Group: Members Posts: 62 Joined: 11-July 11 Member No.: 6058 |
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. |
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Sep 30 2012, 09:47 PM
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Founder Group: Chairman Posts: 14434 Joined: 8-February 04 Member No.: 1 |
It would boil, would it not?
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Sep 30 2012, 11:37 PM
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#3
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Junior Member Group: Members Posts: 85 Joined: 5-September 12 Member No.: 6635 |
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 |
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Sep 30 2012, 11:44 PM
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#4
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Junior Member Group: Members Posts: 40 Joined: 29-December 11 Member No.: 6295 |
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 -------------------- But to be a lament on the lips of the loved one is glorious, For the prosaic goes toneless to Orcus below. (Friedrich Schiller: Naenie)
Home of marspages.eu and plutoidenpages.eu |
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Oct 1 2012, 12:33 AM
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#5
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Junior Member Group: Members Posts: 85 Joined: 5-September 12 Member No.: 6635 |
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 |
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Oct 1 2012, 02:01 PM
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#6
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Senior Member Group: Moderator Posts: 2785 Joined: 10-November 06 From: Pasadena, CA Member No.: 1345 |
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. -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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Oct 1 2012, 05:20 PM
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#7
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Junior Member Group: Members Posts: 85 Joined: 5-September 12 Member No.: 6635 |
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 coo anling 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. Juramike, I have followed your posts for years and have learned a great deal from you, especially the thought experiments you pose. In your opinion what would happen to a glass of water with a temperature of 4c put into that chamber at a pressure of say 12mb. ? ignore other variables for the moment |
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Oct 1 2012, 06:53 PM
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Senior Member Group: Moderator Posts: 2785 Joined: 10-November 06 From: Pasadena, CA Member No.: 1345 |
In your opinion what would happen to a glass of water with a temperature of 4c put into that chamber at a pressure of say 12mb. ? ignore other variables for the moment (Assuming bp. of H2O at 12 mb is at 10 C) It would probably behave similar to a low boiling liquid under terrestrial conditions. I'd use diethyl ether as an example (b.p. 35 C). It won't boil at a normal room temperature of 25 C, but it will evaporate very quickly. As it evaporates, it will cool. Water should do the same thing under vacuum, but water's melting point is pretty high, so it will evaporatively cool and then freeze. After it is frozen it will sublimate. Some wierdness might occur if the glass of water is deep enough, the water would freeze on top and maybe you'd get liquid water sealed up in the ice? (Sublimation will also suck heat out of the system, eventually the whole thing should freeze solid then sublimate.) BTW, a very similar phenomenon is predicted for any Titan ponds of pure methane. They would evaporatively cool, freeze (from the bottom up), then the totally frozen methane pond would slowly sublimate. -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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Oct 1 2012, 07:27 PM
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Junior Member Group: Members Posts: 85 Joined: 5-September 12 Member No.: 6635 |
(Assuming bp. of H2O at 12 mb is at 10 C) Water should do the same thing under vacuum, but water's melting point is pretty high, so it will evaporatively cool and then freeze. After it is frozen it will sublimate. Some wierdness might occur if the glass of water is deep enough, the water would freeze on top and maybe you'd get liquid water sealed up in the ice? (Sublimation will also suck heat out of the system, eventually the whole thing should freeze solid then sublimate.) Do you think it is possible that by exposing the glass to simulated Martian sun the evaporative cooling could be offset enough to keep it liquid until it all evaporated ? |
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