Venus, Earth's closest but mysterious planetary neighbor had become even more of an enigma as discoveries made by the early Soviet probes during the 1960s had shattered earlier beliefs that the similarly sized world was an "Earth-like" planet. Direct measurements left no hope for finding "warm oceans" on the planet's surface as it had been still believed just a decade earlier. The Venera-4 probe, launched in 1967 and designed to withstand around 10 atmospheres of pressure, had been obliterated at an altitude of around 26 kilometers by pressure that reached around 15 atmospheres.
Designers at the Lavochkin bureau in Moscow, who were responsible for the development of Soviet planetary spacecraft, sent reinforced follow-up probes. These spacecraft -- Venera 5 and 6 -- were built to withstand up to 25 atmospheres. The modifications to these landers allowed them to descend as low as 19 kilometers before the atmospheric pressure destroyed them as well. Obviously, not a drop of water could exist on the planet where 500-degree-Celsius surface temperatures were expected.
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