A series of spacecraft launched by the USA during the 1960s and 1970s in a programme to explore the planets Mercury, Venus and Mars. Mariner 2 in 1962 achieved the first successful flyby of Venus, to be followed by Mariner 5 in 1967. Mariner 4, launched in 1964, was the first successful probe to Mars and revealed the presence of craters on that planet. Mariners 6 and 7 followed in 1969. Mariner 9 was put into orbit around Mars in 1971 and returned over 7,000 images. Mariner 10 in 1974 was the first two-planet mission. Its orbit allowed three separate encounters with Mercury, providing 10,000 images, as well as a flyby of Venus. There were a total of seven successful missions in the Mariner series. Numbers 11 and 12 were renamed Voyagers 1 and 2.