Mariner 2 was the world's first successful interplanetary spacecraft. Launched Aug. 27, 1962, on an Atlas-Agena rocket, Mariner 2 passed within about 34,000 kilometers (21,000 miles) of Venus, sending back valuable new information about interplanetary space and the Venusian atmosphere. Mariner 2 recorded the planet's temperature for the first time, revealing the its very hot atmosphere of about 500 degrees Celsius (900 degrees Fahrenheit). The spacecraft's solar wind experiment was the first to measure the density, velocity, composition and variation over time of the solar wind.
Subsequent missions have further explored Venus, detecting electrical activity, which was confirmed by the European Space Agency's Venus Express earlier this week.
Image Credit: NASA/JPL