Mars has been the main attention of astronomers in the hope of finding extraterrestrial life. Several of its properties has led astronomers to such assumptions.     The Martian year is similar to the seasons on earth. In each of the hemispheres a polar cap exists in the fall and winter and diminishes in the spring and summer. Dark regions in the spring have been interpreted as signs of vegetation.
 
 

   Mars is believed to be made of rocky materials similar to the ones on earth.         The atmosphere is thin, only a hundredth as dense as the earth’s atmosphere. Its surface is nearly free of clouds and the features of the Martian surface are therefore not obscured by them. Mars stands midway between the moon and the earth. The surface of Mars is better preserved than the surface of the Earth but less preserved than that of the moon.
 
 

               Mars also stands midway between the moon and the earth in size and mass. It’s mass is about 10 times the mass of the moon and one-tenth the mass of the earth. Mars is about twice the diameter of the moon, and one-half the diameter of the earth.

           Volcanism most likely began around the same time on the earth and Mars. The size of Mars has affected its volcanic activity. Since it is intermediate in size between the earth and the moon it has retained its radioactivity heat longer than the moon, but not longer than the earth, which is still active today. If a planet is small, the heat produced in its interior has to travel only a short distance to reach the surface. This heat escapes quickly and volcanism ends at a young stage in the planets life. If a planet is large, the heat in its interior has a much greater distance to travel. It travels through a thicker layer of rock which acts as an insulating cover for the heat. This heat causes the temperature in the interior to remain at a high level for a long time.

If volcanoes did continue on Mars for over a billion years, its surface would have been covered with water, and a substantial atmosphere would also have existed on Mars. These two factors could’ve been the basis for the evolution of life. In 1976, the Viking spacecraft confirmed the past existence of volcanoes on Mars.

         Mars Global Surveyor is orbiting Mars and sending back reams of info. to Earth; evidence of a once existing ocean on the Northern plains. These are somewhat similar to strandlines visible on earth.
 
 

1960: Nasa Mariner flybys imaged lifeless moonlike surface.

1971: Nasa placed Mariner 9 into orbit around Mars when it was experiencing a giant dust storm.

1972: The storm ended, the dust cleared and Mariner 9 began its complete study of Mars.

1990’s: Martian meteorites, the Mars Pathfinders mission and its famed rover, and Mars Global Surveyor began to refine our search for water.