Pioneer Venus Artwork
Date: 4 Dec 1978
Artist's concept of Pioneer Venus mission approaching the planet.
During a 14-year orbit of Venus, Pioneer Venus 1 used radar to map the surface at a resolution of 75 km (47 miles). It found the planet to be generally smoother than Earth, though with a mountain higher than Mt. Everest and a chasm deeper than the Grand Canyon. The orbiter also found Venus to be more spherical than Earth, consistent with the planet's much slower rotation rate (one Venus day equals 243 Earth days). It confirmed that Venus has little, if any, magnetic field and found the clouds to consist mainly of sulfuric acid. Measurements of this chemical's decline in the atmosphere over the course of the mission suggested that the spacecraft arrived soon after a large volcanic eruption, which may also account for the prodigious lightning it observed.
After a course correction on 16 August 1978, Pioneer Venus 2 released the 1.5-m diameter large probe on 16 November 1978, at about 11.1 million km from the planet. Four days later, the bus released the three small probes while 9.3 million km from Venus. All five components reached the Venusian atmosphere on 9 December 1978, with the large probe entering first.
Data from the probes indicated that between 10 and 50 km, there is almost no convection in the Venusian atmosphere. Below a haze layer at 30 km, the atmosphere appears to be relatively clear. Amazingly, two of three probes survived the hard impact. The so-called Day Probe transmitted data from the surface for 67.5 minutes before succumbing to the high temperatures and power depletion.
Credit: NASA/Rick Guidice