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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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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Nov 15 2007, 07:12 PM
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Founder Group: Chairman Posts: 14434 Joined: 8-February 04 Member No.: 1 |
And of course, the fact that water can exist, at some times, in some places - doesn't mean it does. It is a transient thing and would boil away quite easily - thus it would have to be replenished in some way.
Doug |
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Nov 16 2007, 01:47 AM
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#3
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Member Group: Members Posts: 613 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
And of course, the fact that water can exist, at some times, in some places - doesn't mean it does. It is a transient thing and would boil away quite easily - thus it would have to be replenished in some way. Good thread. I remember I got asked about this one by NPR when the Mars Gullies story first came out. 'Isnt Mars too cold for liquid water?' Well, yes, I answered, and Earth is too cold for liquid rock - doesnt mean it never happens..... Another data point - when I was at the Mars wind tunnel at NASA Ames doing wave generation experiments, I noticed they have a big jar of water in the chamber just inside the window to the control room (wind tunnel is open circuit - inside a large room that gets pumped down). As the pressure drops, the water starts to bump and boil, but then stops, while still liquid. (i.e. it boils until the evaporative cooling brings the temperature well below that at which the saturation vapor pressure equals ambient). We had a big tray of water on which we were hoping to generate waves - we could see on the video link that it bumped once or twice, I guess with bubbles of dissolved air coming out. Then we turned the airflow on in the hope of making waves at 10mbar or so, and saw the water glaze over - the enhancement in evaporative cooling by the airflow was enough to freeze it. Pure water has 6mb vapor pressure at 0 C (and 20mb at 20C - I remember it as 20:20) When I lived in Arizona, this issue of the metastability of water on Earth's surface was rather evident - spill water in the kitchen, no problem, it'll dry up by itself in 3 minutes. At the DPS conference in Monterey (2003?) I raised the question in connection with Titan (known to have 50% or so relative humidity, so where are the oceans?) - I pointed out that Earth is 60% covered in water, and yet we can hang out laundry to dry. Clearly this wouldnt work unless the relative humidity were much lower than 100% (because of circulation to higher altitudes, which dries the air..) Anyway, it remains a subtle issue. I'd urge people read Mike Hecht's work on the topic (he has a rather fresh perspective). And I think Titan (where ethane takes the role of salt, in lowering the saturation vapor pressure of the volatile component in a solution) will be very instructive in comparisons with Mars. So - Doug's words 'transient' and 'replenished' are key - if the system is out of equilibrium, then lots of things are possible. And I guess I am learning over the years that disequlibrium isnt that hard to generate... |
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Nov 16 2007, 01:03 PM
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#4
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
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