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Water on Mars: Freezing or Boiling?

By brainrain in brainrain's Diary
Wed Mar 07, 2001 at 10:52:32 AM EST
Tags: (all tags)

A lake is placed on the surface of mars; will it freeze or boil? This led to a fun debate between a friend and myself, resulting in a surprising ending and conclusion. I'd like to show you the point of views of both sides, along with some evidence, them you can discuss the article amongst yourselves and see what you can come up with. I'll be very interested in the results.

I immediately took the side of freezing, while my friend took the side of boiling. What follows is a compacted version of the debate that took place. Although it was not a formal debate, it was still great fun. Note: The discussion has been edited for content and length.
I immediately opened with: (My arguments will be in regular font.)
There's water on the poles of Mars, which is a commonly known fact!
My friend stated: (My friends arguments will be in Italic font.)
But water cannot exist under a vacuum, which Mars almost has because of the lack of an atmosphere. I remember back in chemistry, we did an experiment where we stuck water in a vacuum, at room temperature, where it then proceeded to boil.
Look, I even have proof! Look at the NASA web site about water on Mars: http://mars.jpl.nasa.gov/msp98/why.html. (Note: You may want to visit this site in another window, just for reference.) "Although liquid water may still exist deep below the surface of Mars, currently the temperature is too low..."
Yes, but did you read the rest of it? "...And the atmosphere too thin for liquid water to exist at the surface. " Because the atmosphere is too thin an entire body of water (lake) cannot exist on Mars, it will begin to evaporate due to the extremely low atmosphere.
But water does exist on the poles! If we were to dump a lake on the pole, wouldn't it freeze?
The water on the poles of Mars contains so many impurities that of course it wouldn't boil away! However, the water, because it has no severe amounts of impurities, would immediately boil due to the air pressure. Besides, the question was "on Mars" not "on the pole(s) of Mars"
I guess NASA would have to take some water up there on their next mission to see what happens!
*sigh*
To the readers: Please give me your standings/information/point of view. If you would like to start a debate of your own, go ahead! If I'm just being ignorant, then please state so below.

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Poll

A lake is placed on the surface of mars; it will...

Freeze. 100%

Boil. 0%

Votes: 2
Results | Other Polls

Water on Mars: Freezing or Boiling? | 5 comments (5 topical, editorial, 0 hidden)

cute lecture demonstration (none / 0) (#1)
by ana on Wed Mar 07, 2001 at 11:11:10 AM EST

There's a rather impressive lecture demonstration we used to do for intro physics classes studying phase changes. You take a flask of water, stopper it, hook up the tubes coming through the stopper to a vacuum pump. In full view of the class, you turn on the pump. The water begins to boil vigorously, more and more and more violently. And then Boink! it freezes, all at once.

So I suppose that's what'd happen to your lake on Mars. The atmospheric pressure isn't quite zero, and the vapor pressure of ice at low temperatures is quite small, so ice can exist there.

Ana

Years go by; will I still be waiting
for somebody else to understand?
--Tori Amos

If the pressure is low enough by Anonymous 242, 03/07/2001 11:40:51 AM EST (none / 0)

Low pressure boiling? (none / 0) (#3)
by jabber on Wed Mar 07, 2001 at 12:23:11 PM EST

The argument that water would boil away on Mars due to low atmospheric pressure, doesn't hold water - forgive the pun. Consider comets. There is no lower pressure than the vacuum of space, yet comets exist and do so in solid form. Granted, they are not pure water, but still, pressure alone doesn't seem to be the controlling factor, despite what I remember from Chemistry.

I suspect that a Marsian lake would freeze, and then sublimate over time. IANAPlanetologist.

[TINK5C] |"Is K5 my kapusta intellectual teddy bear?"| "Yes"

Excellent thought experiment (none / 0) (#4)
by fsh on Wed Mar 07, 2001 at 12:44:42 PM EST

Or Gedankenexperiment, as Einstein used to call it.... I personally think that both would happen. A large body of water would contain too much energy to just freeze immediately, so I imagine that the lake would start to boil while the edges started to freeze. As the lake lost more and more energy, it would flowly freeze over. BTW, the poles are mostly frozen CO2, with some water mixed in.
-fsh

Ice, comets, and water vapor (none / 0) (#5)
by ana on Wed Mar 07, 2001 at 12:54:49 PM EST

OK, here's how it works. I asked google about "phase diagrams for water", and got this, which will do for demonstration purposes.

Surface conditions on mars are cold and low pressure; I'm guessing, but maybe -100 C and 5 millibars? Depending on the weather, day/night, latitude, etc. So that puts us in the lower left corner of this diagram, near the "solid/vapor" line.

There's an equilibrium between water vapor in the atmosphere and solid water on the surface (we're way too cold and low pressure for liquid water). If we're well to the left of the solid/vapor line, it's nearly all solid; if to the right, vapor.

One can construct the curve in detail from a table of vapor pressure vs. temperature for ice. At very low temperatures (few tens of Kelvins, like happen on comets far from the sun) the vapor pressure of ice is very small, so the ice sublimes into vapor very slowly, and we have comets left over from 5 billion years ago when the solar system formed. When the come close to the sun the temperature goes up and the rate is much larger, so often comets only survive a few passages through the inner solar system (after living billions of years way out yonder).

I hope that clears things up a little.

Ana

Years go by; will I still be waiting
for somebody else to understand?
--Tori Amos

Water on Mars: Freezing or Boiling? | 5 comments (5 topical, 0 editorial, 0 hidden)

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