Venera 4

po_Venera4Venera 4 (also designated 4V-1 No.310) was a probe in the Soviet Venera program for the exploration of Venus.

It was the first successful probe to perform in-place analysis of the environment of another planet. It may also have been the first probe to land on another planet, with the fate of its predecessor Venera 3 being unclear. Venera 4 provided the first chemical analysis of the Venusian atmosphere, showing it to be primarily carbon dioxide with a few percent of nitrogen and below one percent of oxygen and water vapors. 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.