Re: Drilling for water on Mars

On Thu, 18 Jun 2009 04:57:07 +0100, Mike Williams
<nospam@xxxxxxxxxxxxxxxxxx> wrote:

Wasn't it John D. Gwinner who wrote:
The significant factor is that the atmospheric pressure on Mars is
slightly below the minimum pressure at which liquid water can exist.
Water exposed to that pressure has to be ice or vapour.

Right. I've read that Mars is pretty close to the tripple point,
especially in low lying areas (Vallis Marinaris, which is close to
where the story would take place).

So you're in favor of the 'freeze rapidly' idea. So if a "Gusher"
poped out, sounds like you think it could entomb the vehicle in ice,
right?

I wish I could get some actual formulaes showing how fast water would
freeze, given a temperature and pressure. I poked around some but
didn't find much.

I'd expect the situation to look something like what happens when you
have a "gusher" of liquid CO2 at Earth atmospheric pressure.

A CO2 fire extinguisher contains liquid CO2, but when you squirt it the
jet is at a pressure where liquid CO2 can't exist. You don't see liquid
CO2 in the jet, only invisible CO2 gas and white clouds of tiny dry ice
crystals. How long does it take the CO2 to freeze? Effectively no time
at all. As soon as it reaches a pressure below the triple point it
cannot be liquid.

IOW, it's not a question of losing heat: some of the liquid becomes
solid, some becomes gas. The heat to turn some into gas comes from the
bits of liquid that become solid. How much each phase change takes
determines the proportions.

There's a significant difference, however, with water on Mars. Because
the atmosphere is only slightly below the triple point of water, it's
possible for the introduction of large amounts of water vapour to push
the local atmospheric pressure above the triple point temporarily. The
size of that effect varies depending on the exact details of the
situation.

So a small *leak* of water won't change the water all at once - but the
proportion of ice to steam should be about the same. Remembering that
the ice and "steam" are at the same temperature. The "steam" isn't hot.

I'm wondering if both ice and steam end up at the same temperature as
the original liquid water was, or whether the expansion makes a
difference. With the CO2 cylinder, the dry ice formed is colder than the
original liquid in the cylinder - so the CO2 gas should be colder too
(until it mixes with the surrounding air).

So I'm guessing you get a spray of ice and steam both of which are
colder than the original water - and there's less atmosphere around to
warm it up to ambient again.

Jonathan

--
http://chromomancer.livejournal.com
.

Relevant Pages

  • Re: Dense fogs in Valles Marineris Mars.
    ... > appears to be a pool of liquid water showing at the far right of the ... pressure at 10 deg C is 9.209 mmHg. ... Since water can only exist in liquid ... level and its average temperature. ...
    (sci.geo.meteorology)
  • Re: Dense fogs in Valles Marineris Mars.
    ... > appears to be a pool of liquid water showing at the far right of the ... pressure at 10 deg C is 9.209 mmHg. ... Since water can only exist in liquid ... level and its average temperature. ...
    (sci.physics)
  • Re: Dense fogs in Valles Marineris Mars.
    ... > appears to be a pool of liquid water showing at the far right of the ... pressure at 10 deg C is 9.209 mmHg. ... Since water can only exist in liquid ... level and its average temperature. ...
    (sci.astro)
  • Re: Drilling for water on Mars
    ... Water exposed to that pressure has to be ice or vapour. ... I'd expect the situation to look something like what happens when you have a "gusher" of liquid CO2 at Earth atmospheric pressure. ...
    (rec.arts.sf.science)
  • Re: Solution to global warming
    ... Europe why don't the build a pipeline to pump water that's ... generated from the melted ice to the centre of the ice caps ... of frozen water it would take to displace one kilo of liquid water. ...
    (rec.arts.drwho)
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