Date: 22 Jul 1962
Artist's concept of an early Mariner spacecraft.
Mariner 2 was the world's first successful interplanetary spacecraft. Launched 27 August 1962, on an Atlas-Agena rocket, Mariner 2 passed within about 34,000 km (21,000 miles) of Venus, sending back valuable new information about interplanetary space and the Venusian atmosphere.
Mariner 2 recorded the temperature at Venus for the first time, revealing the planet's very hot atmosphere of about 900 degrees Fahrenheit (500 degrees Celsius). The spacecraft's solar wind experiment measured for the first time the density, velocity, composition and variation over time of the solar wind.