Pathfinder landed on Mars' surface carrying the six-wheeled Sojourner rover, a mobile robot. Rover and lander took over 17,000 pictures, analyzed rocks and soil, and sent back 8.5 million measurements of the red planet's atmospheric pressure, temperature, and wind. Sojourner was operated from Earth by remote control—but the commands took about six minutes to reach Mars.

Travel time to Mars: 7 months
Touchdown date: July 4, 1997
Operation time: built to last 30 days, worked for 90 days
Purpose of mission: to study rock chemistry, soil chemistry, temperature changes, atmosphere on Mars
Features: lightweight spacecraft carrying advanced camera equipment, scientific instruments, and the Sojourner rover

Image credits: main image, courtesy of JPL, California Institute of Technology and NASA.