Anonymous
Anonymous asked in Science & MathematicsChemistry · 1 month ago

Can large bodies of water  exist on a planet with a 0.05 bar atmosphere?

At that air pressure water boils at 85 degrees. Could large bodies of water say 2 million sq km with a depth of 8,000 feet exist. What if the salt content is 8%?

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  • 1 month ago
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    This is not an issue of boiling point.  The issue is that liquid water has an equilibrium vapor pressure at a given temperature.  If the pressure of the atmosphere is less than the equilibrium vapor pressure, then the water will be driven to vapor in an attempt to make the overlying gas phase come into equilibrium with the water.

    This is where there are problems with your question.  A closed system would see the pressure of the atmosphere rise as water vapor was added.  However, you declare that the atmospheric pressure is fixed.  This means that gas must escape the system, somehow, and thus if water evaporates to try to raise pressure, that water vapor must get lost somehow (otherwise the pressure of the atmosphere would rise).  If water vapor is lost (to space, say), then the liquid will continue to produce more vapor and continue to lose liquid, to vapor, to space, and you won't have any open water bodies.  Eventually, all of the liquid water will be lost to vapor which then escapes the planetary system.

    Given that this is an equilibrium problem, the time frame is somewhat open, so you could have a period where there is still liquid water yet the atmospheric pressure is too low to sustain liquid water.  Time and heat energy are required to see the process to completion, so the situation would be temporary.

    If the planet never had an atmospheric pressure above 0.05 bar, there would never be liquid water on the surface to be exposed to the atmosphere.  It would volatilize relatively instantaneously upon exposure.  There could be ice, however.

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