Pioneer Venus I

Named after the Roman goddess of love and beauty, Venus was first seen through a telescope in 1610 by Galileo. Even with his crude telescope, Galileo was able to determine that Venus goes through phases like Earth’s Moon. These observations helped support the Copernican view that the planets orbited the Sun, and not the Earth, as previously believed. Venus is one of the planets visible with the unaided eye, and is the brightest object in the sky after the Sun and the Moon.
Public Domain Pioneer Venus I Orbiter Image
(Image in public domain)
Fast forward 368 years: On May 20, 1978, the Pioneer Venus I orbiter was launched from the Kennedy Space Center in Florida aboard an Atlas-Centaur rocket. This was the first of a two-spacecraft orbiter-probe combo project designed to conduct a comprehensive investigation of the atmosphere of Venus. The second part of the Venus exploration team was the multiprobe, which was launched on August 8, 1978, and consisted of five separate probes.
Pioneer Venus I took approximately six months to fall into orbit around Venus, and did so on December 4, 1978. It produced the first radar topographic map of most of the planet’s surface, finding it to be relatively smooth and more spherical than Earth. The highest point, Maxwell Montes, was measured at a little less than seven miles above the surface. In comparison for us, the highest point above sea level here is considered Mount Everest, which is roughly 5.5 miles high.
Ready for some heavy scientific jargon? The orbiter also measured the detailed structure of the upper atmosphere and ionosphere of Venus, investigated the interaction of the solar wind with the ionosphere and the magnetic field in the vicinity of Venus, determined the characteristics of the atmosphere and surface of Venus on a planetary scale, determined the planet’s gravitational field harmonics from perturbations of the spacecraft orbit, and detected gamma-ray bursts.
Furthermore (there’s more?!), the orbiter made UV observations of comets and its camera detected almost continuous lightning activity. In 1986, it was able to observe Halley’s Comet when it was not observable from Earth due to its proximity to the Sun.  
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The second half of the dynamic duo, the multiprobe, encountered Venus on December 9, 1978, four months after being launched. The five probes included: the probe transporter (referred to as the Bus), a large atmospheric entry probe (called Sounder), and three identical small probes (called North, Day, and Night). The Sounder released from the Bus on November 15, 1978, and the three small probes released on November 19, 1978.
All the probes entered the Venusian atmosphere within 11 minutes of each other, and took about an hour to descend to the surface. Two of the probes survived impact, and one was able to relay 67-minutes worth of data before being crushed. The data confirmed that the planet’s clouds are composed mainly of sulfuric acid droplets.
In May 1992, Pioneer Venus I began the final phase of its mission, ultimately running out of fuel and being destroyed by atmospheric entry in August of the same year. Data continued to be transmitted to Earth until October 8, 1992, when the mission was officially considered concluded after almost 15 years of studying the second planet from the Sun.
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Happy Anniversary, Pioneer Venus I! Thanks for teaching us so much about our planetary neighbor.

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