The Mariner program was a series of robotic space missions launched by NASA in the 1960s and 1970s. Its primary goal was to explore the planets Venus and Mars. The program included several spacecraft, with Mariner 4 being the first to successfully fly by Mars in 1965, sending back the first images of the Martian surface. Subsequent missions, such as Mariner 6 and Mariner 7, provided more detailed data about Mars, while Mariner 2 was the first spacecraft to successfully fly by Venus in 1962. The findings from the Mariner missions significantly advanced our understanding of these planets.