The surface of Mars, seen from Viking 1, 1976.
© National Aeronautics & Space Administration / Science & Society
In 1975, NASA sent two spacecraft, named Viking, to Mars. After a journey of 10 months, the spacecraft orbited the planet, taking pictures from which landing sites were selected. On 20th July, 1976, Viking 1's lander touched down on the Martian surface, followed on 3rd September by Viking 2. The landers photographed their surroundings, analysed the soil, and made meteorological observations, while the orbiters photographed the entire planet's surface and measured atmospheric water vapour. The primary aim of the mision was to search for any evidence of life on Mars, past or present. None was found, but analysis of the Martian landscape did suggest that water may have been present in considerable quantities in the past.