Mars -- atmospheric pressure

[gunsandrockets]

I know that atmospheric pressure on the surface of Mars ranges from 1 milibar to 12 milibars because of ground elevation and seasonal changes. And that Martian air pressure at 400,000 feet above ground level is similar to the Earth at the same altitude.<br /><br />So how does the pressure vary by altitude on Mars? On one hand Mars gravity is lower, but on the other hand carbondioxide is heavier than nitrogen. So I know it's a little complicated.

 

[mithridates]

I don't know the exact ratio to altitude and pressure but here's the Wikipedia article on the lowest part of the planet, which has a much higher presssure than the rest:<br /><br />http://en.wikipedia.org/wiki/Hellas_Basin <br /><br />Here's the relevant part:<br /><br />The altitude difference between the rim and the bottom is 9 km (5.6 Miles). The depth of the crater (4 km (2.4 Miles) below the topographic datum, or "sea level" of Mars) explains the atmospheric pressure at the bottom: 840 Pa (8.4 mbar) (.25 InHG). This is 38% higher than the pressure at the topographical datum (610 Pa, or 6.1 mbar or .18 InHG). The pressure is high enough that water is speculated to be present in its liquid phase at temperatures slightly above 0 °C (32 F). <div class="Discussion_UserSignature"> <p>----- </p><p>http://mithridates.blogspot.com</p> </div>

 

[JonClarke]

This calculator is supposed to allow you to calculate atmospheric pressure at different altitudes on different planets.<br /><br />The zero datum on Mars is the 6 millbars, the pressure for the triple point of water. All altitudes below datum therefore can support liquid water, provided it's warm enough. All areas coloured green or blue on this map are below datum. How long the liquid water actually hangs round in these areas will depend on humidity as well as temperature (the boiling point is very low at these pressures).<br /><br />Jon<br /><br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[gunsandrockets]

"This calculator is supposed to allow you to calculate atmospheric pressure at different altitudes on different planets."<br /><br />Just what I was looking for, thanx! <br />

 

[gunsandrockets]

Hellas is a fascinating area. The pressure figure you referenced for Hellas is, I believe, just an average. The pressure is even higher during the southern warm season, because so much of the southern polar cap evaporates that the atmospheric pressure on Mars increases by a third!