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 °F (-60 °C).Temperatures at the Martian surface vary from as low as about -195 °F (-125 °C) near the poles during the winter to as much as 70 °F (20 °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 two years. (Mars Science, 2000)
Mars has many of the kinds of surface features that are common on Earth. These include plains, canyons, and volcanoes. Overall, craters occur throughout the surface of Mars, while they are rare on Earth. In addition, fine-grained reddish dust covers almost all the Martian surface.
Many regions of Mars consist of flat, low-lying plains. Most of these areas are in the northern hemisphere. They may be so smooth because they were built up from deposits of sediment. There is evidence that water once flowed across the Martian surface. The water would have tended to collect in the lowest spots on the planet and thus would have deposited sediments there.
Near the equator of Mars, there are is a string of canyons known as Valles Marineris. Scientists believe that they were formed by the crust of the surface being stretched and ultimately split. Volcanoes appear throughout the planet. Many of these volcanoes resemble volcanoes that are in Hawaii. Their slopes rise gradually and they are referred to as shield volcanoes. They were formed from eruptions of lavas that can flow for long distances before solidifying. (The Surface of Mars, 2002)
Martian craters are similar to craters on Earth’s moon. The craters have deep, bowl-shaped floors and raised rims. Some large craters have central peaks that form when the crater floor rebounds upward after an impact. Much of the surface of the southern hemisphere is extremely old, and it contains many craters. Other parts of the surface, especially in the northern hemisphere, are younger and thus have fewer craters. (Mars, 2002)
The Surface of Mars. (2002). Canyons and plains. [Online]. Available: http://www.nasm.si.edu/ceps/etp/mars/surface.html
Mars Atmosphere. (2002). [Online]. Available: http://chapters.marssociety.org/polska/mars_atmosphere.html