Mars Odyssey was put into orbit around Mars in 2001 to study its geology and environment and to detect the presence of underground water.
Pathfinder
Pathfinder landed on Mars in the summer of 1997. There, it deployed a small all-terrain vehicle named Sojourner to study the composition of the surface.
Mariner
Mariner 10 photographed the surface of the planet Mercury three times in the mid-1970s, revealing a world quite similar to that of our Moon.
