Viking Orbiter 1, launched August 20, 1975, reached its orbit around Mars June 19, 1976. Its cameras began photographing the planet -- standard operating procedure for an orbiting probe. But in this case, the orbiter was using these photos to determine a safe place for its onboard lander to touch down.
July 20, 1976, Lander 1 made its incredible descent to the planet's surface. September 3 Lander 2 was released from the second of the twin Viking orbiters and set up camp at a site 4,014 miles away from its on-ground counterpart.
Orbiters and landers in position, Viking was ready to unlock the secrets of Mars.
Viking orbiters mapped practically the entire planet; more than 51,000 photos were taken. From their vantage point above the planet, scientific equipment on the orbiters detected water vapor in the atmosphere and tracked its seasonal changes, mapped the seasonal temperature changes of the planet's surface, polar caps and clouds, and measured the density of the Martian atmosphere.
During the landers' descent, experiments were conducted to determine the composition of the Martian atmosphere and study the ionosphere, the layer above the atmosphere made up of charged particles. Once on the surface, the three-legged Viking began taking black and white, color and stereo photographs. Meteorological equipment returned the first extraterrestrial weather report. Seismometers were set up to detect "Marsquakes." An X-ray Fluorescence Spectrometer determined the composition of the Martian soil and the landers scooped up samples to test for life in their one cubic foot biological labs.
The Viking lander labs were an amazing technological wonder. Crammed into a tiny space was the most sophisticated scientific hardware ever developed. The labs were intended to fulfill the main mission objective -- investigate the possibility of life on Mars.
Three experiments searched for evidence of metabolic processes, and a Gas Chromatograph/Mass Spectrometer, which can find organic molecules in even the most barren of Earth soils, tried to detect organic molecules that could be the precursors or remains of living organisms.
The Viking combination of twin orbiters and landers was a masterpiece in planetary probe technology, not to mention an effective research tool. From July 1976 to November 1982 when the last of the four Viking craft transmitted its final message, the wide angle view of the orbiters and the up-close contact of the landers provided the most extensive information on Mars yet gathered.
