Less than four years after NASA launched its first successful orbiter to Mars, the space agency sent twin orbiter-landers to the red planet – Viking 1 launched Aug. 20, 1975, and Viking 2 launched Sept. 9, 1975.

Designed to study martian geology, seismology and meteorology, and

biology – or the lack thereof – the two Viking spacecraft provided researchers with a comprehensive model of Mars.

Design and development for the Viking program began in 1968 at NASA’s Langley Research Center in Hampton, Va. There, the project was managed by James Martin, the former assistant manager for the Lunar Orbiter Project


NASA’s Pasadena, Calif.-based Jet Propulsion Laboratory (JPL) built the solar-powered Viking orbiters, which were based on NASA’s first successful Mars orbiter, Mariner 9.

While Langley managed the overall mission, JPL managed the science mission.

In establishing technology and protocols to search for martian life, the team focused on what they knew – the simplest form of life known on Earth: micro-organisms. To carry this out the Viking spacecraft carried

a biology processor that looked for evidence of photosynthesis, bacteria and organic compounds.

After Viking 2 launched from Cape Canaveral, Fla., on an Atlas-Centaur rocket, it reached orbit around Mars Aug. 7, 1976, a little less than a month after Viking 1. Then on Sept.

3, the lander detached from the orbiter. The lander

performed a soft landing on the martian surface, slowing its descent by using a combination of parachutes and retro rockets.

The orbiters measured the amount of water vapor in the atmosphere and performed infrared mapping. They also amassed more than

16,000 high-resolution photographs, mainly of Mars. Unlike the Viking 1 orbiter’s orbit, the Viking 2 orbiter flew in an inclined orbit above the equator to take photographs of the polar regions and within 22 kilometers of Mars’ smaller moon Deimos.

The orbiters also supported the landers by scouting potential landing sites and by serving as communication relays for them.

The Viking 2 lander touched down in the Plain of Utopia, 7,360 kilometers from Viking 1 in the Plain of Chryse.

Together the plutonium-powered landers sent more than 1,400 high-resolution images back to Earth. They also gathered and analyzed soil samples, measured seismographic activity, temperature and wind.

Although the landers found no conclusive signs of life, the results were cause for excitement. The three biological experiments they performed detected

unexpected chemical activity within the soil. Scientists explained that the planet is “self-sterilizing” because it is bombarded by ultraviolet radiation, and it


soil moisture and the tendency of the soil to oxidize. These factors are believed to prevent the development of organisms in the soil.

The Viking mission more clearly revealed

what previously had been evidenced by the Mariner 9 probe. The mission

showed Mars is a planet divided horizontally by plains in the north and cragged highlands in the south. The frozen desert planet generally sees temperature swings from minus

14 degrees Celsius at day to minus

120 degrees Celsius at night.

The Viking orbiters found large – now dormant – volcanoes, seasonal dust storms and the exchange of atmospheric gases between the polar caps where they also

observed evidence of frozen water.

Both landers easily surpassed their expected 90-day operational lifetimes

. The Viking 2 lander ceased communicating Apr. 11, 1980, while the Viking 1 lander kept sending data back to Earth until

Nov. 13, 1982.

Viking 1 still holds the record as the longest-lasting spacecraft to

continue operating after it reached the surface of Mars

, but it might soon be surpassed if NASA’s Mars Exploration Rovers continue to operate on the martian surface.

The Opportunity Rover already has surpassed Viking 2’s operational lifetime and

Spirit is close behind.