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This drawing shows that Mars has an atmosphere very different from the atmosphere on Earth.
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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 axis (25 degrees) are similar to those on Earth (24 hours and 23.5 degrees), the orbit of the planet about the Sun affects 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 small 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 surface of the planet. With so little water, clouds are rarely seen in the Martian sky. The possible role in the 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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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF