Once many astronomers thought that the seasonal changes of Mars's su rface seen from earth were due to growing and dying vegetation. The photographs transmitted to the earth by the Mariner and Viking flybys, orbiters, and landers between 1965 and 1976 revealed a waterless, crate red planet that in many ways was similar to but in many other ways was different from both the moon and the earth.
The fine, delicate streaks called "canals" and sketched by observers on early Martian maps are illusory. The Mariner and Viking pictures revealed these canals to be nothing more than dark-floored craters or irregular dark patches aligned by chance and linked unconsciously by early observers into lines that looked like canals.
Viking 1 and 2 were two of the most sophisticated pieces of technical hardware in the space effort. Both arrived in the vicinity of Mars in the summer of 1976 after a 10-month journey. From orbit each detached a lander that sat down on the surface of Mars and began to collect information. Although the two orbiters and one of the landers have ceased to operate, analysis of their data will continue for many years to come. All outlived their expected useful life and have provided us with a wealth of information about the surface terrain, atmosphere, biological activity, and satellites of the red planet Mars.
