On December 14, 1962, after a three-and-a-half-month journey of 293 million kilometres from Earth, NASA’s Mariner 2 spacecraft, approached Venus. Forty-four minutes before closest approach – at a distance of 34,773 kilometers from Venus, Mariner’s 2 radiometers began to scan the planet’s dayside.
On January 3, 1963, twenty days after passing Venus, Mariner 2 transmitted half an hour of telemetry and then went silent. Radio contact was lost for ever. Mariner 2 became a mute piece of metal, endlessly circling the Sun in a heliocentric orbit.
Mariner 2 was the first spacecraft to successfully flyby another planet. The mission was an outstanding success and it created a great deal of publicity. William Pickering, the director of the Jet Propulsion Laboratory, which was responsible for designing Mariner 2, found himself featured on the cover of Time Magazine and rode as Grand Marshall of the Tournament of Roses Parade in Pasadena.
In the meantime, the scientific debate over what Mariner 2 might find at Venus had been intensified. Radio observations in the 1950s gave rise to two interpretations – an extremely hot planet, with surface temperature at least at 342°C or a planet with a relatively benign surface temperature. But all the evidence from Mariner 2 seemed to confirm the high surface temperature interpretation. Venus was a hellish world. Ground temperatures were as high as 428oC (800oF). There was no evidence of a magnetic field around the planet and they couldn’t detect any water vapour in its atmosphere. Five years later, Mariner 5 revealed a thick cloud-covered planet with even higher temperatures and a crushing atmosphere.