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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Oct 1 2012, 09:04 PM
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Newbie Group: Members Posts: 5 Joined: 20-August 12 From: Knoxville, TN Member No.: 6595 |
I searched the web and couldn't find a phase diagram for water that showed the “area of interest” in much more detail than the one that Udo posted up-thread, so I created my own using Excel and the equations found here:
http://www.iapws.org/relguide/MeltSub2011.pdf (Eqns 1 and 6) and here: http://www.iapws.org/relguide/IF97-Rev.pdf (Eqns 29b and 30) I have attached a couple of phase diagrams for water over the different ranges of temperatures and pressures that have been discussed. I used the “max pressures” as estimated by Eyesonmars for Hellas and Gale at summer solstice. As djellison said, we are indeed “dancing around a tiny tiny wedge.” I have also attached the values in tabular format: As Udo noted, if the pressure is below the triple-point of water (6.11657 mBar = 6.11657 hPa = 611.657 Pa), then it doesn't matter the temperature, there can be NO pure liquid water on the surface. Of course, this all is based on pure water. Impurities (e.g., salts) change both the boiling point (usually elevated) and freezing point (usually depressed) at a given pressure. I couldn't find any easily accessible (and understandable to me) information on how the phase diagram changes with molality, particularly at these low pressures. Maybe someone else can find some Mars-specific info. At Earth pressures, very salty water (think Dead Sea) doesn't freeze until -20 C or lower (from the CRC Handbook of Chemistry and Physics for a 4.6 M solution of NaCl). The boiling point is less affected -- it elevates about +2 C for a 4 M solution. So, as others have said, liquid water on Mars today seems POSSIBLE, but probably short-lived, if it exists at all. I’m not going to worry too much more about the fate of glasses of pure water on Mars -- I’m going to put on my brand new, VERY cool, red-cyan clip-on, flip-up glasses and go see if I can talk anyone else in the family into imagining what the waterfalls and rushing waters of Gale Crater could have been like a couple of billion years ago. Mark |
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Oct 2 2012, 07:59 AM
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#3
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Senior Member Group: Members Posts: 1089 Joined: 19-February 05 From: Close to Meudon Observatory in France Member No.: 172 |
I used the “max pressures” as estimated by Eyesonmars for Hellas and Gale at summer solstice. As djellison said, we are indeed “dancing around a tiny tiny wedge.” I have also attached the values in tabular format: GREAT post Mshell ! For your info, the max pressure measured by VL2 for its entire mission was 10.72 mb on Sol 277... => Could you, please, adjust your last (and nice) table ? ==> Besides, what would be the max pressure at Hellas at Winter solstice ? (I guess your 14 mb figure is valid for the lowest part of Hellas at -8530m altitude) Warm welcome and thanks again ! |
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Oct 2 2012, 06:09 PM
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#4
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Junior Member Group: Members Posts: 85 Joined: 5-September 12 Member No.: 6635 |
GREAT post Mshell ! For your info, the max pressure measured by VL2 for its entire mission was 10.72 mb on Sol 277... ==> Besides, what would be the max pressure at Hellas at Winter solstice ? As mshell stated, he took the value of 10.2mb from one my earlier posts. I believe i stated that this is representative of the maximum DAILY MEAN surface pressure at the Viking 2 site As the subsequent discussion has shown there is still some uncertainty in what the EXTREME max pressure might have been. As Vikingmars points out this occurred around LS 280 at the VK2 site. ( I think it was LS and not SOL, as you stated. Correct me if I'm wrong. The max pressure occurred around SOL277 at Vk1 and LS277 at VK2 ) My purpose was to show how difficult it is for liquid H2O to exist ANYWHERE on Mars, let alone at the MSL site. So using the only long term meteorological surface data we have I estimated what the pressures might have been at Gale and Hellas on that day. ( I even rounded off the scale ht to 11km) I know this is getting off topic admins so if you think a new topic is warranted I understand.. But back to the Viking data. It is interesting that the max pressure (and wind speed) at the VK2 site occured as a global dust storm engulfed the lander. While this is very pronounced at the VK2 site it is a hardly noticible at the VK1 site. In addition, the diurnal temperature fluctuations drop to almost nothing by Martian standards ( 10-15c). Given that the surface can disappear as seen from orbit during a major storm I will go out on a limb and predict that Curiosity will no longer be able to see Mt. Sharp if we have a major/global storm - and for many months afterwords.. If so, our image experts Might have to make due for a while ( not to mention the loss of HiRise imaging ...) |
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