Mariner 2 successfully launches on a mission to Venus. It is to become the first spacecraft to fly by another planet.

During its journey to Venus, the craft for the first time measures the solar wind, a constant stream of charged particles flowing outward from the Sun. It also measures interplanetary dust, which turns out to be more scarce than predicted. In addition, Mariner 2 detects high-energy charged particles coming from the Sun, including several brief solar flares, as well as cosmic rays from outside the solar system.