Mariner 2

Mariner 2 became the first successful mission to another planet when it flew by Venus on December 14, 1962. The spacecraft made a number of discoveries about the planet and marked another first by measuring the solar wind, a constant stream of charged particles flying outward from the sun.

Five years later, Mariner 5 followed up on Mariner 2's study of Venus with a closer look at the planet's atmosphere.