# Martian atmosphere

Martian atmosphere
Surface pressure 7-13 mb
Carbon dioxide 95.3%
Nitrogen 2.7%
Argon 1.6%
Oxygen 0.13%
Carbon monoxide 0.07%
Water vapor 0.03%
Nitric oxide 0.01%
Neon 2.5 ppm
Krypton 300 ppb
Xenon 80 ppb
Ozone 30 ppb
Methane 10.5 ppb

The Martian atmosphere does not include any gases that are not also present in Earth's atmosphere, although the proportions are different.

The most noticable difference, apart from the low atmospheric pressure, is that over 95% of the Martian atmosphere is carbon dioxide, compared to 365 ppm on Earth. It is cold enough during the Martian winter that the carbon dioxide freezes out of the atmosphere to form polar ice caps.

## Structure

Mars upper atmosphere has been probed by the use of accelerometers on the Viking landers and other space probes, yielding profiles of its density. Using theoretical models of its temperature, the pressures in the upper atmosphere can also be estimated using the formula:

$\rho = {P \over W R T}$

where:
$\rho$ is the air density
P is the ambient air pressure
W is the mean molecular weight of the martian atmosphere
T is the ambient temperature
R is the universal gas constant (8.314 J/K-mol)

From the data obtained by the Viking landers, the following profiles can be derived:

 Viking 1 Viking II h (km) P (mb) T (oC) P (mb) T (oC) 120.0 0.00000414 -136.85 0.00000199 -157.15 108.0 0.00001840 -126.75 0.00001300 -152.05 96.0 0.00008020 -127.25 0.00006600 -122.95 84.0 0.0003870 -128.95 0.0002880 -131.75 72.0 0.002050 -134.05 0.001680 -142.25 60.0 0.009110 -127.65 0.008540 -135.85 48.0 0.04450 -124.55 0.03920 -102.45 36.0 0.1980 -107.05 0.1580 -108.75 28.0 0.4830 -89.35 0.4040 -99.95 4.5 5.160 -51.05* 5.222 -51.95 4.0 5.390 -50.53 5.483 -51.55 3.5 5.635 -48.45 5.747 -51.05 3.0 5.885 -46.65 6.015 -50.55 2.5 6.150 -44.85 6.282 -50.05 2.0 6.427 -43.05 6.564 -49.55 1.5 6.707 -41.35 6.853 -49.15 1.0 6.994 -39.45* 7.160 -48.55* 0.5 7.301 -37.65* 7.480 -48.05* 0.0 7.620 -35.85* 7.820 -47.55*

The existence of this and other data has allowed the production of a standard atmosphere model for Mars, which is useful in planning landings on that planet.