The Viking probes of the mid-1970's deployed the landers that became pioneering explorers and returned the first images of the surface of the Red Planet. Mars, while appearing nicely terrestrial (like Earth), has conditions far different than those on our world.
What we found was a cold, barren, rocky, desert planet. When our two worlds formed several billion years ago, they may have shared similar conditions. Mars, at one time, had a vast quantity of water, a thicker atmosphere, and a warmer climate than it does now. Surface temperatures on Mars resemble Earth's more than any other planet. Equatorial temperatures can get all the way up to 77 degrees F, but only around noon on the warmest day of the Martian summer. At night, temperatures drop to well below freezing.
Martian air--comprised mostly of carbon dioxide, much like that of Venus--leaves much to be desired. As if the carbon dioxide didn't make breathing hard enough, the air is thinner than the air found at an altitude of 19 times higher than Denver, Colorado.
Photo. These island-shaped terrain features demonstrate evidence of flowing water. Courtesy of NASA, JPL.
Vikings 1 and 2 noticed signs that indicated liquid water may have once existed on Mars. Now, almost all of the water lies frozen beneath the surface. Pictures show giant flood channels, dry river beds, and flood plains on the surface. Could these be indications that water once flowed on the Martian surface? Is it possible that life once existed there? Or does it still exist? We hope to find answers to these questions with future missions to Mars--notably human expeditions--and with the study of Martian rocks that have found their way to Earth.
Photos. A Viking orbiter image showing a network of tributary channels. Courtesy of NASA, JPL.
Mission to Mars. An educational site created for the ThinkQuest contest.