THE SURFACE OF MARS

T he atmosphere and surface of Mars is very diverse. Carbon dioxide makes up the majority of the Martian atmosphere at about 95.3%. Other elements that are present are nitrogen at 2.7% and argon at 1.6% The average surface pressure of the atmosphere is less than 1/100th of the average surface pressure of Earth's atmosphere. The Martian atmosphere undergoes dramatic daily and seasonal temperature changes. It averages about 220 K (-64 degrees F) and varies from 145 K (-199 degrees F) during the polar night to 300 K (80 degrees F) at the equator during midday at perihelion.

M ars has great seasonal changes due to its position in orbit, much like that of Earth. A jet stream has also been observed on the surface. During certain seasons dust is blow around and forms awe inspiring storms. One such storm was recorded that completely covered the Martian surface.

T he color of the Martian surface ranges from orange to brownish black. The darker material is weathered basaltic rock and the lighter is iron oxide. The color of the Martian landscape changes seasonally which indicates that the majority of the surface is covered b dust deposits that are easily transported by wind. Photographs of the Martian surface provided by the U.S. Viking landers confirm the presence of windblown deposits across the surface.

T here are three distinct periods in the history of the Martian landscape. The first is the Noachian Period which was a time of heavy bombardment by meteors and comets which formed the lunar like, ancient cratered highlands of Mars. Hellas and Argyre are the largest well-preserved impact basins of the period. Characterized by volcanic activity the next period in the history of the Martian landscape was the Hesperian Period. Constant lava flows carved channels in the planets surface and volcanoes constantly erupted sending debris high into the planets atmosphere. The last period is the Amazonian Period. During this time large shield volcanoes like Tharsis and Elysium. The largest shield on Mars, Olympus Mons, is more than 15,900 m (52,000 ft) high and 600 km (370 miles) across, having roughly the same area as the state of Arizona. These times of great change helped to create the Martian landscape that we see today.