1965 the Mariner deep space probe sent back the first photographs
showing Mars to have a desolate, cratered surface with an atmosphere
far thinner than expected, exerting only 1% that of the Earth's
air pressure at sea level and consisting mostly of carbon dioxide
- a place where liquid water could not exist.
In 1976 Viking
1 landed in Chryse, a rock strewn area of sand-dunes. The Martian
sky was pink, not the familiar blue, due to a fine dust suspended
in the atmosphere.