Atmosphere of Mars

The atmosphere of Mars is very thin. Its density is about 1.2% of the density of the Earth's atmosphere. The mean atmospheric pressure at zero level is 6 hPa (0.006 bar). This is only 0.6% of the mean atmospheric pressure on Earth, which is 1013 hPa (1.013 bar), and is about the same as the pressure prevailing in the Earth's stratosphere at an altitude of 32 km.

The extremely low atmospheric pressure is close to the triple point of water. This means that liquid water can only exist on the surface of Mars in lowlands (these are mainly the northern hemisphere and Hellas Planitia) and only at high temperatures for a few hours. At the lowest point on the Martian surface in Hellas Planitia, the pressure reaches a maximum of about 12 hPa (0.012 bar). This is well below Armstrong's limit of 63 hPa (0.063 bar), at which water boils at human body temperature, so a human cannot survive on Mars without a pressure suit or pressurized cabin.

In its chemical composition, the Martian atmosphere, like that of Venus, consists mainly of carbon dioxide, along with other gases such as argon, nitrogen and oxygen. In 2003, traces of methane were also detected in the planet's gas envelope. Until now, it has not been possible to clearly explain how this gas entered the atmosphere.

Although the atmosphere of Mars is so thin, the Martian sky is not black. Because of the high amount of dust in the atmosphere, light is strongly scattered. The daytime sky appears bright and stars are not visible. The color of the day sky varies from orange-red to pink and purple to blue near the rising and setting sun.

Structure

The Martian atmosphere is structured as follows:

• Lower atmosphere
• Middle Atmosphere: This stage contains the Martian jet stream.
• Upper atmosphere, also called thermosphere: This is where the highest temperatures in the Martian atmosphere occur, due to solar radiation. Here the gases begin to separate and no longer form the uniform mixture of gases found in the lower atmospheric layers.
• Exosphere: Begins at an altitude of about 200 kilometres above the surface of Mars. This is where the planet's atmosphere merges into space. There is no fixed upper limit of the atmosphere, it merges smoothly into space.

Potential use by humans

The atmosphere could be an important resource for manned Mars missions in the future.

For example, it would be conceivable to develop a device that can split the carbon dioxide in the atmosphere into elementary carbon and oxygen. In this way, the oxygen for the astronauts' breathing air or as a fuel component would not have to be taken from Earth at great expense. A corresponding experiment called MOXIE, which produces carbon monoxide and oxygen from carbon dioxide at high heat, is planned as part of the Mars 2020 rover mission, which landed on Mars in February 2021. The first five grams of oxygen could be produced on 20 April 2021.

The same mission will also use the Martian atmosphere for flight tests. To this end, it brought the 1.8 kg helicopter Ingenuity to the surface of Mars. The helicopter made its first autonomous flight on 19 April 2021 and will take photos of the environment in the future.