A question here, behaviour of water on Mars |
A question here, behaviour of water on Mars |
May 24 2007, 12:38 AM
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#1
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Junior Member Group: Members Posts: 58 Joined: 17-September 06 Member No.: 1150 |
A question here
There are signs that in the past there was liquid water on Mars. So lets assume thats true. Since the gravity on Mars is much lower than on Earth, so how does water (waves) behave on Mars compared to Earth? Someone did say, that waves would have been much higher but also much slower. Is this true? Does anyone have an animation where you can see a waive on Earth in comparsion to a wave on Mars? Thanks |
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May 25 2007, 04:52 PM
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#2
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Dublin Correspondent Group: Admin Posts: 1799 Joined: 28-March 05 From: Celbridge, Ireland Member No.: 220 |
On earth the average atmospheric pressure of ~101kPa is a pretty powerful hydrodynamic pump - it is equivalent to a 10m water column. The martian atmosphere is only 1% of that - even accounting for the lower gravity there the equivalent water column on Mars is only 23cm (at most). Large storm surges like the one you describe require a low pressure zone surrounded by a high pressure zone all over the same body of water. Say we had such an item (e.g. the hypothetical northern Martian ocean) then even an extreme hurricane like storm with a 20% internal pressure drop would only be capable of pushing a surge of a handful of centimeters.
It must be said though that _if_ there was an ocean like that then the atmosphereic pressure would have had to be significantly higher - at these sort of pressures it would just boil away. If that was close to Earth like pressures then the storm surges would be massive - 2-3x what we see on Earth from a similar storm. |
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Nov 15 2007, 06:14 PM
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#3
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Member Group: Members Posts: 401 Joined: 5-January 07 From: Manchester England Member No.: 1563 |
I have a question I've not been able to resolve and here seems the best place to ask it: The atmospheric pressure of mars is around the triple point pressure of water, hence on a day of high atmospheric pressure and a temperature above freezing (or with the right impurities) a puddle of liquid water could remain on the surface as liquid , but with a very reduced boiling point compared to earth? That is what a great many articles I have recently read seem to assert or imply. However a chemist friend of mine has just argued to me that the triple point pressure on the phase diagram is the partial pressure of water vapour, and since on mars a H2O partial pressure above 6.1 millibars is almost impossible to build, liquid water is indeed impossible on mars! He is quite convinced, but I find it difficult to accept that so many journals and articles have been mistaken over such a fundamental fact. In fact I have read papers on experiments showing that brines at least can remain stable and liquid at mars atmospheric pressure
water2.pdf ( 134.75K )
Number of downloads: 1272
, but I am at a loss to explain how this is possible to my friend! EDIT:So you all know I'm not just being lazy, I've googled and wikipediad and gone to the university library, and although I've found both versions I've not found anything that clarifies the difference, or addresses the question directly. -------------------- |
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Nov 15 2007, 11:30 PM
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#4
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Member Group: Members Posts: 384 Joined: 4-January 07 Member No.: 1555 |
I have a question I've not been able to resolve and here seems the best place to ask it: The atmospheric pressure of mars is around the triple point pressure of water, hence on a day of high atmospheric pressure and a temperature above freezing (or with the right impurities) a puddle of liquid water could remain on the surface as liquid , but with a very reduced boiling point compared to earth? That is what a great many articles I have recently read seem to assert or imply. However a chemist friend of mine has just argued to me that the triple point pressure on the phase diagram is the partial pressure of water vapour, and since on mars a H2O partial pressure above 6.1 millibars is almost impossible to build, liquid water is indeed impossible on mars! He is quite convinced, but I find it difficult to accept that so many journals and articles have been mistaken over such a fundamental fact. In fact I have read papers on experiments showing that brines at least can remain stable and liquid at mars atmospheric pressure
water2.pdf ( 134.75K )
Number of downloads: 1272 , but I am at a loss to explain how this is possible to my friend! EDIT:So you all know I'm not just being lazy, I've googled and wikipediad and gone to the university library, and although I've found both versions I've not found anything that clarifies the difference, or addresses the question directly. Marsbug - An excellent (and not uncommon) question. The phase diagram for water, with its triple point at 6.1 millibars of pressure, is for the one component system H2O. For that simple system, liquid water is transiently possible at pressures higher than this, initially for a ridiculously small range of temperatures of only a few degrees C, with an increasing range possible at higher pressures, up to the entire 100 degree range between freezing and boiling possible at terrestrial atmospheric pressure. At low martian pressures, this means that at lower elevations you could melt ice to liquid, heat it a degree or two, and it would begin to boil. That is, liquid water might be stable at low elevations, but not very. Consider an atmosphere with constituents other than steam, however, and the picture gets more complex. The atmosphere on Mars is mainly dry CO2. Unless it is actively snowing, or condensing frost, the humidity of this atmosphere is less than 100%, so liquid water (or even ice) will be metastable (transient), like it is in Phoenix, Arizona in June. That is, it won't boil, but it will tend to evaporate (for liquid) or sublimate/melt (for ice). This isn't to say people in Phoenix can't maintain swimming pools (or cold drinks by the poolside) in June, but they have to keep replacing the evaporative losses (or ice in the drinks). At the extremely cold temperatures of Mars, metastable ice can persist for rather a long time, and liquid water, if it were not actively boiling, might also. But your chemist friend is correct, liquid water would not be stable, just metastable. Next consider the effect of dissolving salts, especially chloride salts, in liquid water. At any pressure, this simultaneously lowers the freezing point ("freezing point depression" familiar to those who salt down their icy sidewalks in winter) and raises the boiling point (one reason why most cooking recipes call for adding salt to the water BEFORE boiling). To thermodynamicists, dissolved salts do this by greatly lowering the activity of H2O in the liquid. Some salt mixtures, particularly those rich in calcium chloride, can lower freezing temperatures to more than 50 degrees C, to temperatures commonly found on Mars. Under these conditions, liquid brine would be stable, or at the very least could persist for extremely long times, despite low humidity (concentrated brines are hygroscopic, meaning they can actually suck moisture out of air). Paul Knauth and I wrote a couple of papers on this topic in 2002 and 2003, in which we suggested that the "young gullies" on Mars could have been carved by such multicomponent chloride brines (so-called eutectic brines), which normally would be expected beneath permafrost or ice layers. I just submitted an impact-related update to this idea to the Mars gullies workshop upcoming in Houston on Feb 4-5. To your friend the chemist, everything is either stable or unstable. Geologists consider that most of the world we observe is actually metastable (like diamond jewelry is, if you understand the phase diagram for carbon, or read old Superman comic books). And I fear that, despite my best intentions, I've been as clear as mud. Edit: minor change to text as per following post by Gsnorgathon about too salty food. -- HDP Don |
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Nov 16 2007, 12:41 AM
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#5
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Member Group: Members Posts: 259 Joined: 23-January 05 From: Seattle, WA Member No.: 156 |
Not to rain (metastably or otherwise) on anyone's parade (least of all dburt's after such a wonderfully detailed post), but I strongly suspect that most recipes call for salt to be added before boiling so that whatever's being boiled will absorb the salt, and thus enhance its flavor.
I'd guess that an amount of salt sufficient to raise the boiling point would be a tad much for most people's taste. |
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