Venera 4

Venera 4 (Russian: Венера-4, lit. 'Venus-4'), also designated 4V-1 No.310, was a probe in the Soviet Venera program for the exploration of Venus. The probe comprised a lander, designed to enter the Venusian atmosphere and parachute to the surface, and a carrier/flyby spacecraft, which carried the lander to Venus and served as a communications relay for it.

In 1967, it was the first successful probe to perform in-place analysis of the environment of another planet. Venera 4 provided the first chemical analysis of the Venusian atmosphere, showing it to be primarily carbon dioxide with a few percents of nitrogen and below one percent of oxygen and water vapors. While entering the atmosphere it became the first spacecraft to survive entry into another planet's atmosphere. The station detected a weak magnetic field and no radiation field. The outer atmospheric layer contained very little hydrogen and no atomic oxygen. The probe sent the first direct measurements proving that Venus was extremely hot, that its atmosphere was far denser than expected, and that it had lost most of its water long ago.