The Soviet Missions to Venus

Up until the spacecraft got there they still didn't know that it was a hellscape? No, we had no way of measuring the planet's temperature from here. And without knowing that it's a planet with sulfuric acid clouds and temperatures of many hundreds of degrees, you just can't figure that out. The American Mission Mariner 2 did a fly by in 1962 and it had two purposes. It was measuring the magnetic field which really wasn't there and it was measuring the temperature - 490 to 590 degrees Kelvin.