Mariner 2 was the first successful mission to another planet by any country. Launched just 36 days after the failure of its twin, Mariner 1, it flew by Venus as planned at a range of 34,762 km (21,600 miles), scanning the planet’s atmosphere and surface for 42 minutes.
The spacecraft showed that surface temperature on Venus was at least 797 degrees Fahrenheit (425 degrees Celsius) on both the day and night sides, hot enough to melt lead. It also showed that Venus rotates in the opposite direction from most planets in our solar system, has an atmosphere mostly of carbon dioxide with very high pressure at the planet’s surface, continuous cloud cover, and no detectable magnetic field. It also found the solar wind streams continuously and that the density of cosmic dust between planets is much lower than it is near Earth.