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.

(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.

Earl Colby Pottinger

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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"...
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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;'

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.

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