Experiments under Mars conditions show water could remain liquid down to -20C to -50C in salt solutions:

Water Could Stay Liquid on Mars.
By Bjorn Carey
15 November 2005
"Using a planetary environmental chamber - a tank that mimics the atmosphere, temperature, and pressure of other planets - the team exposed various concentrations of briny water to conditions that match Mars' colder, less pressurized environment. Based on these experiments, salty water, it seems, can exist as liquid on Mars.
"It was thought that any liquid on the surface would evaporate almost immediately,' Julie Chittenden, a graduate student with the Arkansas Center for Space and Planetary Sciences told SPACE.com. 'These brine solutions enable water to stay liquid at colder temperatures. If you expose these brine solutions to cold temperatures, they can exist for a very long period of time.'
"While pure water freezes at zero degrees Celsius, water mixed with sodium chloride and calcium chloride salts - the two salts used in these experiments - remains liquid down to -21 and -50 degrees Celsius respectively."
http://www.space.com/scienceastronom...e_tuesday.html

The Phoenix lander is to land in the Mars north polar region. It might be thought there would be little chance for liquid water here.
But this report shows modeled maximal temperatures on Mars according to latitude:

Title: On the possibility of liquid water on present-day Mars.
Journal: Journal of Geophysical Research, Volume 106, Issue E10, p.
23317-23326 (JGR Homepage)
Publication Date: 10/2001
http://www.agu.org/pubs/crossref/200...JE001360.shtml

It appears in Fig. 4 on page 23,231. The maximal temperature at 70 degrees North latitude is given as 250 K, -23 C.
This is below the freezing point of pure water but the experiments show it is in the range for liquid water brines. This fact is also discussed here:

Making a Splash on Mars.
"On a planet that's colder than Antarctica and where water boils at ten
degrees above freezing, how could liquid water ever exist? Scientists
say a dash of salt might help."
...
"One thing we have to be careful of is our everyday experience that
water always freezes at zero degrees," noted Hoover. "It doesn't.
Water containing dissolved salts freezes at a significantly lower
temperature. Don Juan Pond in Antarctica is a good example. It's a
high salinity pond with liquid water at temperatures as low as -24 °
C."
http://science.msfc.nasa.gov/headlin...st29jun_1m.htm

Some images of Don Juan Pond:

http://www.science.siu.edu/microbiol.../DJP.view.JPeG

http://www.science.siu.edu/microbiol.../M2JC.DJP.JPEG

Some reports argue there is no life in Don Juan Pond but this article discusses life found on its periphery:

An extraterrestrial habitat on Earth: the algal mat of Don Juan
[correction of Jaun] Pond.
Adv. Space Res. 1983; vol. 3, 8:39-42.
http://www.ncbi.nlm.nih.gov/entrez/q..._uids=11542753


Bob Clark

Hell we can tuna in brine! We can start a tuna factory on Mars :-)

Hello all, and happy new year. Nice to join this forum!
My two cents would be that actual pools of brine would be extremely rare, as to remain liquid at martian high latitude temperatures brines would need to be 30%+ salts. That doesnt rule out more modest occurences, such as thin films between grains etc, and it's wise never to say never when dealing with a planetfull of the unknown.

Gosh, I hope it does. Welcome to BAUT, Marsbug.

__________________
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Rovers forever! - ToSeek

In addition, to the citation I gave that gives modeled North polar temperatures, this report gives actual TES measurements during Summer in Fig. 3:

Summer season variability of the north residual cap of Mars as observed by the Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES).
W. Calvin and T. Titus.
Planetary and Space Science
Volume 56, Issue 2, February 2008, Pages 212-22
http://dx.doi.org/10.1016/j.pss.2007.08.005

It shows 255K being reached as far north as 75N latitude, so would get even higher at the approx. 70N latitude of the Phoenix landing site.
The attached image below which is a blow up of Fig.1 from the report:

Factors Influencing the Location of Sustained Cold, Bright Spots in the North Residual Cap of Mars.
J. M. Pocock, W. M. Calvin
Seventh International Conference on Mars (2007), Abstract #3210
http://www.lpi.usra.edu/meetings/7th...7/pdf/3210.pdf

also shows 255K being reached at 75N latitude, so even higher at 70 N latitude.


Bob Clark

http://sitelife.space.com/ver1.0/Con...b443.Large.jpg

It's 20 degrees and 1000mbar in my living room. No brine though.

Point being, just because a set of environmental conditions which would temporarily allow brine to exist, that doesn't mean it will. At the very warmest, you'll never be far from the triple point, ice isn't going to melt in an instant (it takes an ice cube a long time to melt in a 4 deg C refrigerator) and if it's warm enough to melt it'll probably be warm enough to sublimate. It's a very small wedge in the phase diagram for liquids at that temp and pressure regime.

COULD Phoenix see liquids. It's physically possible. Will it? I don't think so. Why would Phoenix find liquid brine, when orbital assets have not? Phoenix will have a few square metres to investigate. HiRISE, CRISM, MOC, HRSC, THEMIS, CTX have covered literally millions of square kilometers with every observation with no obvious liquids visible. Why would Phoenix be any different?

Doug

In that image from the report "Factors Influencing the Location of Sustained Cold, Bright Spots in the North Residual Cap of Mars" I linked, the legend showing the temperature ranges isn't very clear. Heres a larger version.


Bob Clark

Attached Images

TES-ver3.jpg (108.6 KB, 12 views)