The United States sent two probes to Mars, Viking 1 and Viking 2. Scientists believed dark spots on the planet might be simple forms of life. The Viking probes were sent to collect samples and conduct experiments to see whether life really did exist on Mars, to take pictures of the planet’s surface, and to determine what Mars’ atmosphere was made out of.

The Viking probes had two main parts: an orbiter and a lander. The Orbiter had two TV cameras. The Lander was a three-legged spacecraft that fit inside a shell for protection and carried all the scientific instruments.

Viking 1 was launched September 9, 1975 and went into orbit around Mars on June 19, 1976. Viking 2 was launched August 7, 1976. They carried television cameras that took 26,000 photos of Mars and its moons, Phobos and Deimos. The Viking orbiter cameras mapped most of Mars’ surface, helping NASA find potential landing sites for the Viking landers. The pictures showed volcanoes, huge canyons, craters, and evidence that Mars once had water. The landers parachuted to the surface on July 20 and September 3, 1976. The television camera showed a red rocky surface, a dusty pink sky, sand dunes, and no large life forms. As the landers fell towards the surface of Mars, they measured the planet’s atmosphere. It was made up mostly of carbon dioxide and some nitrogen. The soil was found to be mostly silicon and iron. Temperatures ranged from –14 degrees C (5.4 degrees F) during the day in the summer to –120 degrees C (-196 degrees F) at night during the winter. The unmanned landing on Mars came seven years to the day after the first Apollo manned landing on the Moon.

One important mission for Viking was the search for life on Mars. The landers carried many instruments designed to detect evidence of life on the planet. Each Lander had a robotic arm that had a scoop at the end. These were used to pick up dirt samples and put them into a mini-chemistry lab for tests. The Viking probes found no evidence of life, but it could not prove that life never existed on Mars.

The weather stations on the Landers did find that Mars is much colder than Earth. Since Mars is farther from the Sun than Earth and it has a thinner atmosphere, temperatures fell to –166 degrees F at night and could only rise to about 70 degrees F at the equator.

The Viking probes were made to only work for 6 months, but they ran much longer. Lander 2 continued to work until 1980, and Lander 1 continued to send back pictures until 1982.

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Unless otherwise noted, all images courtesy of NASA. Permission for use at http://www.nasa.gov/gallery/photo/guideline.html.

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