This drawing represents several features of the atmosphere on Mars including: dust storms, an atmospheric pressure much lower than found on Earth, and a composition primarily of carbon dioxide.
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Lower Atmosphere

The atmosphere of Mars is much thinner than that of Earth, with a surface pressure averaging 1/100th that at the surface of the Earth. Surface temperatures range from -113oC at the winter pole to 0oC on the dayside during summer.

Although the length of the Martian day (24 hours and 37 minutes) and the tilt of its rotational axis (25 degrees) are similar to the values for these parameters on Earth (24 hours and 23.5 degrees), the eccentric orbit of the planet about the Sun impacts the lengths of the seasons the most. The atmosphere is composed mainly of carbon dioxide (95.3%), nitrogen (2.7%), and argon (1.6%), with trace amounts of other gases. Oxygen, which is so important to us on earth, makes up only 0.13% of the atmosphere at Mars. There is only one-fourth as much water vapor in the atmosphere.

Although small, this is thought to be enough to allow water ice to be frozen into the near subsurface at mid to high latitudes. With so little water, clouds are rarely seen in the Martian sky. The possible role in the distant past of liquid water in forming the dry river beds which we can see is still unknown, particularly because water ice is not plentiful on the surface of the planet.

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