Two identical probes landed on Mars in 1976 within weeks of each other, while their orbiter mother ships mapped the planet and made other measurements.
The Viking 1 and 2 landers were the first spacecraft to take photographs from the surface of the Red Planet. Both carried a series of experiments to test for life in the soil. Despite early promising results, NASA scientists ultimately concluded they had not detected life.
Photo: The Utopian Plain on Mars taken by the Viking 2 lander (NASA)
Two probes search for Martian life.
The Viking lander lifts rocks in the search for Martian life.
Viking mission scientists looking for life in Mars's soil made one last attempt by lifting a rock with the probe's sampling arm and running tests on the soil beneath. It was thought that the rocks on Mars might shelter life from the Sun's UV radiation.
Gentry Lee introduces the instruments aboard Viking.
Scientist and writer Gentry Lee gives a brief rundown of the instruments on the Viking landers and explains why the spacecraft are true robots.
Twin probes take close-up pictures of the planet's rock strewn surface.
The unmanned Mars probes Viking 1 and 2 landed on the Red Planet's surface in 1976 and returned photographs of a world littered with volcanic rock. Seismometers aboard the craft suggested that the planet is no longer geologically active.
US spacecraft return the first photos taken from Mars's surface.
In 1976 the United States Viking spacecraft successfully returned the first complete photographs taken from the Martian surface.
American probes look for microbes in Martian soil.
The first spacecraft to land on Mars were the American Viking 1 and 2 probes in 1976. Their mission included testing the planet's soil for life. However, despite promising early test results, life was not found.
The Viking program consisted of a pair of American space probes sent to Mars, Viking 1 and Viking 2. Each spacecraft was composed of two main parts: an orbiter designed to photograph the surface of Mars from orbit, and a lander designed to study the planet from the surface. The orbiters also served as communication relays for the landers once they touched down.
It was the most expensive and ambitious mission ever sent to Mars, with a total cost of roughly US$1 billion (roughly US$3.8 billion in FY14 dollars). It was highly successful and formed most of the body of knowledge about Mars through the late 1990s and early 2000s.
The Viking program grew from NASA's earlier, even more ambitious, Voyager Mars program, which was not related to the successful Voyager deep space probes of the late 1970s. Viking 1 was launched on August 20, 1975, and the second craft, Viking 2, was launched on September 9, 1975, both riding atop Titan III-E rockets with Centaur upper stages. Viking 1 entered Mars orbit on June 19, 1976, with Viking 2 following suit on August 7.
After orbiting Mars for more than a month and returning images used for landing site selection, the orbiters and landers detached; the landers then entered the Martian atmosphere and soft-landed at the sites that had been chosen. The Viking 1 lander touched down on the surface of Mars on July 20, 1976, and was joined by the Viking 2 lander on September 3. The orbiters continued imaging and performing other scientific operations from orbit while the landers deployed instruments on the surface.