Atmosphere of Mars

Not such a bad place to visit, and you couldn't live there.
Mars has a thin atmosphere:

Here is a comparison of the atmospheric composition of Earth and Venus and Mars. I list the number of molecules per m2 of surface area of the planet in each planet's atmosphere relative to the total number of molecules per m2 in Earth's atmosphere.

          Earth       Venus        Mars
N2        0.79         2         3 x 10-4
O2        0.20       < 0.001     10-7
Ar        0.01         0.005     2 x 10-4
CO2       0.0003      64         0.009
H2O     ~ 0.02       ~ 0.01      ~10-6

Total     1.00        90         0.01

H2O      3 km        0.5 mm        small
+ vapor

(A technical note: This is based on a pressure ratio of 0.0056/1,
a surface gravity ratio of 0.38/1.0, and a mass per molecule
ratio of 1.5/1.0 for Mars/Earth.)
Note that Mars has more carbon dioxide in its atmosphere than does Earth, but Mars has a lot less of everything else.

In cold weather, find H2O frost on the surface.

There is CO2 ice in polar caps. Most of it evaporates in summer.

Water ice in the polar caps. Maybe some under the surface. But how much?

How about liquid water?

Really, it can't exist?

Where did the atmosphere go?

ASTR 121 Home
Davison E. Soper, Institute of Theoretical Science, University of Oregon, Eugene OR 97403 USA