

Essay by terri1975smithUniversity, Bachelor's February 2003

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The atmosphere above the surface of Mars is about 100 times less dense than the atmosphere of Earth. The Martian atmosphere is dense enough to support a weather system that includes clouds and winds. According to experts, Mars' roller coaster-like weather is more chaotic and unpredictable than scientists first thought. At times, the sky can appear pink and cloudless, filled with windblown dust raised from the rusty Martian surface. Tremendous dust storms sometimes rage over the entire planet. Most of the dust storms occur during the perihelion - when Mars is closest to the sun. In addition, the dust storms continue to dominate the atmosphere and climate during the aphelion - when Mars is furthest from the sun. Perihelion and aphelion occur every Mars year, which equals two Earth years. (Mars Atmosphere, 2002)

Mars is much colder than Earth. The average temperature on Mars is about -80 ÃÂ°F (-60 ÃÂ°C).Temperatures

at the Martian surface vary from as low as about -195 ÃÂ°F (-125 ÃÂ°C) near the poles during the winter to as much as 70 ÃÂ°F (20 ÃÂ°C) at midday near the equator. (Mars Science, 2000)

These shifts in climate are caused by three factors: Mars' thin atmosphere, its elliptical orbit around the sun, and strong climatic interactions between dust and water ice clouds in the atmosphere. Mars' atmosphere is so thin that it weighs less than 1 percent of Earth's atmosphere. Because Mars' atmosphere is so paper-thin and there are no oceans to store up heat from the sun, the planet's temperatures respond more quickly and intensely to surface changes and atmospheric heating by the sun. There are also much larger annual changes in sunlight falling on Mars than on Earth, because Mars' distance from the sun varies by 20 percent in its orbit around the sun every...