In 1974, NASA’s Mariner 10 became the first space probe to fly by Mercury.
Mariner 10 was launched on November 3, 1973. It was also the first spacecraft mission to visit two planets and the first spacecraft to use the gravitational pull of one planet (Venus) to reach another (Mercury).
Learn more at http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1973-085A
