Mars is actually wetter than Antarctica is at some times.

[exoscientist]

You frequently hear said Mars is much drier than any place on Earth as an indication of the difficulty of having liquid water on Mars, as in this news release:<br /><br />Deep down, Mars harbors a lot of ice <br />Frozen water may even be drinkable, scientists say.<br />"Mars is extremely dry, drier than any (place) we have on Earth," said Gerhard Neukum, a German scientist who has analyzed stereo images of the Martian surface recorded by the European Space Agency's Mars Express satellite that began orbiting the fourth planet from the Sun in late 2003."<br />http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2005/12/06/MNG8RG3HH31.DTL&feed=rss.news<br /><br />However, during southern Winter, Antarctica can actually have less atmospheric water vapor than the highest concentrations of water vapor on Mars:<br /><br />South Pole Transmissivity Plots. <br />"Because of its high altitude, low water vapor column, and low temperatures, Antarctica may contain some of the driest and thus best sites for infrared, submillimeter, and millimeter astronomy [Bally, 1989; Harper, 1989; Chamberlin and Bally, 1996]. Potential sites on the Antarctic plateau vary in elevation from nearly 3000~m to over 4000~m. The center of the plateau is in a permanent high-pressure zone where air is descending from high altitudes. Temperatures at the south pole range from 200~K to 260~K [Chamberlin and Bally, 1994]. Measurements of the precipitable water vapor column [e.g., Smythe and Jackson, 1977; Burova et al., 1986] show that the water column can be as low as 50 microns in the austral winter, and is rarely above 1~mm." <br />http://casa.colorado.edu/~bally/AT/cara.html<br /><br />The term "precipitable microns" means the thickness of liquid water you would have if the entire water vapor content in a column were conde <div class="Discussion_UserSignature"> </div>

 

[najab]

So, in other words, the wettest place on Mars is just about as wet as the driest place on Earth....

 

[exoscientist]

I like to say it is wetter.<br /><br /><br /> - Bob <div class="Discussion_UserSignature"> </div>

 

[exoscientist]

An even better image of these dense clouds/fogs is given in this report on Mars Express:<br /><br />Adsorption water driven processes on Mars. <br />D. Möhlmann <br />http://sci.esa.int/science-e/www/object/doc.cfm?fobjectid=36779 [pdf file]<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[exoscientist]

You can't take off your helmet safely at 30,000 ft on Earth either, the height airliners fly at. But that doesn't mean liquid water can't exist there. It can. - Bob <div class="Discussion_UserSignature"> </div>

 

[exoscientist]

The point is at 30,000 ft. the pressure is very low and temperature is very low. As is well known from cases where airliners have lost cabin pressure at those altitudes, death for humans can result in seconds.<br /> However, bacterial life does survive there and liquid water does exist there.<br /> The conditions on the surface of Mars are comparable to the conditions at such high altitudes on Earth where actively metabolizing life and liquid water are known to exist.<br /><br /><br /> - Bob <div class="Discussion_UserSignature"> </div>

 

[silylene old]

Well Mt. Everest is actually 29,035 feet high, so this 30,000 foot height not being on the surface of the earth argument is not really that absurd of an argument, given rounding errors. So let's consider it further.....<br /><br />The atmospheric pressure on Mt. Everest is about 285 torr in July, and 255 torr in May (when it is usually climbed). The PO2 (partial pressure of O2) at this pressure is usually considered to be the threshold of survival for a well-adapted healthy male. http://jap.physiology.org/cgi/content/full/86/3/1062 The pressure in mid-winter drops another 10 torr, and at this lower pressure, the peak cannot be reached without oxygen tanks. In fact, the peak experiences rather wide and fast variations in pressure as low-pressure fronts pass, and these pressure changes can be fatal without supplemental O2. Wise climbers actually use forecasts to intentionally pick days of high atmospheric pressure to make the final unassissted peak ascent.<br /><br />A height of 9144 m (30,000 ft) would give an atmospheric pressure of 242.5 torr (according to the well established equation: pressure = exp (6.63268 - 0.1112 h - 0.00149 h^2), h = height in km), So 30,000 feet would be just below the accepted threshold of survivability pressure. I really doubt at 30,0000 death would <font color="yellow">"occur within seconds"</font>for a well-adapted healthy male. It would probably take hours, with a long unconscious period.<br /><br />Interestingly, if it rained on Mt Everest, raindrops would not splash. There was an interesting paper on this subject earlier this year in <i>Nature</i>, IIRC. Below a certain threshold atmospheric pressure (about 500 torr), a falling drop of water colliding with a planar surface will not generate smaller rebounding microdroplets. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[exoscientist]

I was using "30,000 ft." as the approximate altitude airliners fly at. It might actually be the range of 30,000 to 40,000 feet. From reports I've read, after loss of cabin pressure, unconsciousness results in seconds and death soon after, perhaps actually minutes.<br /><br /><br /> - Bob <div class="Discussion_UserSignature"> </div>

 

[silylene old]

Well, I posted data for 30,000 feet! <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>