Mariner 9 was the first spacecraft to orbit another planet, photographing Mars for nearly a year beginning in late 1971. When the craft arrived at the Red Planet, huge dust storms totally obscured the surface. But eventually the dust cleared, and Mariner 9 transmitted 7,329 images, covering more than 80 percent of Mars' surface.

One striking view was a mountain of unimaginable proportions.

"We saw for the first time that huge volcano that we now call Olympus Mons." Van der Woude said. "Nothing like that has been seen before or since in the solar system."

Olympus Mons soars 15 miles (24 km) above the surface, dwarfing the largest terrestrial volcano, Mauna Loa, which is just 6 miles (9 km) high, including the portion of the volcano that extends underwater to the sea floor.