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Surface Water Possible Under Mars-Like Conditions
Doug Haxton wrote:
stmx3 wrote in message ... Waitaminute...the pressure of the Martian atmosphere is only about 1% that of Earth's at sea level, right? Wouldn't any surface water just boil away? Doug Not necessarily...especially if the water is cold. At 70 deg F, you can lower pressure slowly down to about 10 Torr before vigorous boiling occurs. If you keep lowering below 4.5 Torr, suddenly you'll get a rapid phase transition to ice because you're at the Triple Point of water. So, if water is colder, you should be able to lower pressure even further before you get boiling. How much is 10 Torr in terms inches of mercury? Doug 1 Torr = 1 mmHg = 1/25.4 inHg. So, 10 Torr ~ 0.4 inHg. |
#13
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Surface Water Possible Under Mars-Like Conditions
In article ,
Gordon D. Pusch wrote: ...I think it would be quite a trick to get measurements of things like this in the time available. Moreover, there is ABSOLUTELY NO REASON to believe reduced gravity should have any effect on the evaporation rate of water, any more than it would affect the boiling point or freezing point of water. It wouldn't affect the fundamental evaporation rate, given the scale at which that operates, but it conceivably might affect convection phenomena, and they determine what relative humidity a given evaporation rate will produce in the near-surface air... which in turn affects the evaporation rate. That is, at the level of the whole system, it might have some effect. But there is a point where you just have to say "that is too much trouble to try to allow for right now"... -- MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer first ground-station pass 1651, all nominal! | |
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Surface Water Possible Under Mars-Like Conditions
Earl Colby Pottinger writes:
(Gordon D. Pusch) : (Henry Spencer) writes: In article , Jens Kieffer-Olsen wrote: I take it that gravity on Mars being a mere 38% of that in the experiment has little bearing on the evaporation rate? Very little. And as a practical matter, it's virtually impossible to reproduce that anyway... Airplanes in free fall are used to produce brief periods of zero gravity, so why not let a slight trust emulate .38G? No need for a slight thrust; emulating lunar or Martian gravity is just a matter of flying a slightly shallower parabola. It's been done occasionally. But the available time at reduced G is too short for some things; I think it would be quite a trick to get measurements of things like this in the time available. Moreover, there is ABSOLUTELY NO REASON to believe reduced gravity should have any effect on the evaporation rate of water, any more than it would affect the boiling point or freezing point of water. Gravity is quite simply UTTERLY IRRELEVANT to any process governed by microscale physics. Gravitation is only important when bodies are large and/or all other accelerations are small --- neither of which are true of individual molecules of water. Sorry, you are wrong. If a large body of water is boiling in a low pressure enviroment the portion of the water that is boiling is the water under less pressure than it's vapor pressure at it's temperture. With a large/deep body of water the gravity in part determines how far down the water is boiling. The less the gravity, the more that boils at a time. Look: We are =NOT= talking about "large bodies of water," we are talking about _EVAPORATION FROM THE SURFACE OF DAMP SOIL_. Such phenomena are VERY clearly controlled by MICROPHYSICS, SURFACE PRPERTIES, and WIND SPEED --- =NONE= of which have any =INTRINSIC= dependence on surface gravity !!! If you use a psychrometer on Mars, gravity is =NOT= one of the things you will need to "correct" for !!! -- Gordon D. Pusch perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;' |
#15
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Surface Water Possible Under Mars-Like Conditions
JRS: In article , seen in
news:sci.space.science, Henry Spencer posted at Sun, 21 Sep 2003 01:28:48 :- In article , Gordon D. Pusch wrote: ...I think it would be quite a trick to get measurements of things like this in the time available. Moreover, there is ABSOLUTELY NO REASON to believe reduced gravity should have any effect on the evaporation rate of water, any more than it would affect the boiling point or freezing point of water. It wouldn't affect the fundamental evaporation rate, given the scale at which that operates, but it conceivably might affect convection phenomena, and they determine what relative humidity a given evaporation rate will produce in the near-surface air... which in turn affects the evaporation rate. Indeed. Wet air is lighter than dry air, so increased gravity will remove it faster. That reduces the date at which water that has just evaporated out will fall back in. Moreover, evaporation cools. Above 4 C, gravity helps evaporation by removing cool water from the top; below 4 C it hinders. -- © John Stockton, Surrey, UK. / © Web URL:http://www.merlyn.demon.co.uk/ - FAQish topics, acronyms, & links. Correct = 4-line sig. separator as above, a line precisely "-- " (SoRFC1036) Do not Mail News to me. Before a reply, quote with "" or " " (SoRFC1036) |
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