Posted to sci.astro:

From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Re: Mars temperatures - they're doing it again!
Newsgroups: sci.astro, alt.sci.planetary, alt.astronomy, sci.geo.geology, sci.astro.amateur
Date: 2002-03-27 21:18:18 PST

The article "Contamination of Mars", by Carl Sagan, Elliott C. Levinthal, Joshua Lederberg, Science, 15 March 1968, vol. 159, no. 3820, p. 1191-1196,
is available online:

http://www.profiles.nlm.nih.gov/BB/A/B/J/H/_/bbabjh.pdf

On pages 11-13 according to the PDF numbering, they argue that pools of liquid water might be exposed during the hottest part of the day and frozen over as temperatures fall, and also thin liquid water films might form from melting frost on the surface of sufficient duration to
be biologically useful for microbes on Mars.

Bob Clark

rgregoryclark@yahoo.com (Robert Clark) wrote in message news:<832ea96d.0203231435.7b7e5618@posting.google.com>...
> "Mike Dworetsky" <mike@platinum198.u-net.com> wrote in message news:<at3n8.241$7L2.443417@newsr2.u-net.net>...
> > ...
> > I thought it was not just the temperature, but the very low atmospheric
> > pressure, that means that liquid water can't exist on Mars. If it gets too
> > hot on the surface for ice to stay frozen, it just evaporates. In which
> > case, the remark above is still true at the S. Pole, but it would never be
> > liquid.
> >
> > You might get liquid during some big melting event, but that water would
> > very quickly evaporate or freeze.
> >
> > I could be wrong, so if anyone knows for sure, let us all know!
> >
>
> The idea that liquid water would immediately evaporate on Mars
> was based on theoretical calculations. Pressures in the northern
> hemisphere at least are routinely above the 6.1 mbar triple point
> for water. This is also the case at some low elevation sites in the
> southern hemisphere such as Argyre basin, Hellas basin, and
> Valles Marineris. Then liquid water could possibly be stable at
> these locations as long as the temperature did not rise too far for
> the low pressures on Mars.
>
> Here's NASA scientist Chris Mckay on the issue:
>
> Can Liquid Water Exist on Present-day Mars?
> "At the surface the frost may melt to form a very short-lived layer
> of liquid," says McKay. "The experiments show that this is the
> case." But, he cautions, "how long it persists is not yet accurately
> determined.
> "There have been several attempts to look at the problem of frost
> evaporation and melting on Mars theoretically," says McKay. But
> Levin's analysis, he says, is "badly flawed. The way to address
> this question," he says, "is with experiment."
> http://nai.arc.nasa.gov/index.cfm?page=liquid_water
>
> Carl Sagan has performed such experiments:
>
> "Experiments under Martian pressures and temperature cycling,
> and with a variety of wind velocities, performed in the laboratory
> of one of us (C.S.), tend to support the conclusion that thin layers
> of liquid water are generally formed each morning at tropical
> latitudes on Mars when diffusion is limited. A variety of
> experiments (23) indicates that many terrestrial microorgansms
> can grow, even if liquid water is available for only 15 minutes
> each day, in otherwise subzero conditions; or in soil
> microenviroments where liquid water is available as a
> consequence of freeze-thaw cycling."
> "Contamination of Mars"
> Carl Sagan, Elliott C. Levinthal, Joshua Lederberg
> Science, 15 March 1968, vol. 159, no. 3820, p. 1191-1196
>
> Berkeley scientist Lawrence Kuznetz also has performed
> experiments showing thin liquid films could be stable under
> Martian conditions:
>
> APPROACHES TO RESOLVING THE
> QUESTION OF LIFE ON MARS
> http://www.biospherics.com/mars/2000SPIEFinal.html
>
> As described on this page this experiment is one that could be
> repeated in any university physics lab. And Kuznetz has
> performed the experiment with Berkeley students:
>
> Life on Red Planet May Exist
> Students suggest `films' of liquid water present on Mars
> http://www.dailycal.org/article.asp?id=2466&ref=news
>
> There was also an experiment showing that flows of liquid water could
> occur under current Martian conditions, which suggests the
> Malin/Edgett gullies might be forming currently:
>
> Martian Outflow Channel Formation by Water Erosion Under
> Nonequilibrium Conditions
> Abstracts of the Lunar and Planetary Science Conference, volume 20,
> page 666, (1989)
> http://adsabs.harvard.edu/cgi-bin/bib_query1989LPI....20..666M [full
> text]
>
> Note also that given the daytime temperatures indicated by TES and
> THEMIS you might expect above freezing temperatures to diffuse down
> through the Martian soil at least a few centimeters. Then you might
> have liquid water of centimeter or larger thickness protected by the
> Martian soil from the thin atmosphere and cold nighttime temperatures.
>
> A report in the Proceedings of the NAS also gave regions on Mars
> where liquid water might be stable at least for short times during the
> day:
>
> Use of spacecraft data to derive regions on Mars where liquid
> water would be stable
> Proc. Natl. Acad. Sci. USA, Vol. 98, Issue 5, 2132-2137, February
> 27, 2001
> http://www.pnas.org/cgi/content/full/98/5/2132
>
>
> Bob Clark