The Mariner Series
A Mariner is a spacecraft designed to visit other planets. NASA called this program The Mariner Series.
Mariner 1 & 2
Mariner 1 & 2 were the same models. They had different missions, Mariner 1 was supposed to go to Mars, and Mariner 2 went to Venus.
Mariner 3 & 4
Mariner 3 & 4 were also identical. They both had the same mission, but only Mariner 4 succeeded. Their missions were to get a closer look of Mars.
Mariner 5, 6 & 7
Mariner 5 got a closer look at Venus. Mariner 6 & 7 were identical, and got an even better look at Mars than Mariner 4. They were also launched only 31 days apart.
Mariner 8, 9 & 10
Mariner 8 & 9 were also identical, but Mariner 8 shut down 365 seconds after the launch. Mariner 9 was the first spacecraft ever to orbit a planet. Mariner 10 was the last Mariner, and it was also the first spacecraft ever to visit Mercury.
Mariner 9 Orbits Mars
NASA Anniversary: Launch of Mariner 2, August 27, 1962
Launch of Mariner 5 Spacecraft to Explore Venus
Mariner Spacecraft to Mars