"[T]hroughout the 60s, 70s, and 80s our understanding of Venus slowly increased in depth and sophistication. But still the clouds did not clear, and major mysteries remained. The early Soviet efforts produced a string of failures...Venera 3 — actually reached Venus only to crash into the planet on March 1, 1966...the first successful mission Venera 4, reached Venus in October 1967 — first planetary probe to enter the atmosphere of another planet, do direct experiments and radio home the results...During its brief (ninety-four –minute) decent by parachute, the spacecraft measured conditions in and below the clouds, confirming that the atmosphere of Venus is mostly carbon dioxide and recording increasing temperature and pressure...at an altitude of more than sixteen miles."