The image below is a mosaic of Mariner 9 frames, taken during the spacecraft's first orbit of Mars, showing the south polar cap dimly through the great dust storm. The polar caps displayed seasonal variations, and study revealed clear signs of radical long-term climate changes.
After a few weeks, the dust settled and the first of over 7,000 pictures began to be transmitted back to Earth. Previously unknown Martian features were revealed, including evidence that large amounts of water once flowed across the surface, etching river valleys and flood plains.
The image below is Valles Marineris, the great canyon of Mars. This canyon is over 3,000 miles long and 5 miles deep.
