Mariner 5: return to Venus

Launched four months before, NASA/JPL’s unmanned Mariner 5 space probe reaches the planet Venus. With its cameras removed to make way for other instrumentation, Mariner 5 provides valuable data on the makeup of the Venusian atmosphere and the probable conditions on the surface, corroborating what the Soviet Union’s successful landing of Venera 4 had found: a planet whose dense atmosphere traps heat and carbon dioxide, resulting in oven-like temperatures and ground-level pressures. NASA attempts to keep Mariner 5 functioning months after its flyby of Venus for tandem measurements of solar wind with Mariner 4, which has now passed beyond Martian orbit, but contact cannot be reliably maintained with Mariner 5 long enough to conduct the experiment.