Orbiters
Launch: August 20, 1975 (Viking 1); September 9, 1975 (Viking 2)
Arrival: June 19, 1976 (Viking 1); August 7, 1976 (Viking 2)
Mass: 2,325 kilograms (5,125 pounds) with fuel
Science instruments: High-resolution camera, atmospheric water-vapor mapper, surface heat mapper,
occultation experiment
Landers
Landing: July 20, 1976 (Viking 1); September 3, 1976 (Viking 2)
Mass: 576 kilograms (1,270 pounds)
Science instruments: Biology instrument, gas chromatograph/mass spectrometer, X-ray fluorescence
spectrometer, seismometer, meteorology instrument, stereo color cameras, physical and magnetic properties of
soil, aerodynamic properties and composition of Martian atmosphere with changes in altitude
Overview
NASA's Viking Project found a place in history when it became the first mission to land a spacecraft successfully on the surface
of another planet and return both imaging and non-imaging data over an extended time period.
Two identical spacecraft, each consisting of a lander and an orbiter, were built. Each
orbiter-lander pair flew together and entered Mars orbit; the landers then separated and descended to the planet's
surface.
The Viking 1 lander touched down on the western slope of Chryse Planitia (the Plains of Gold), while the Viking 2 lander settled down at
Utopia Planitia.
Besides taking photographs and collecting other science data on the Martian surface, the two landers conducted three
biology experiments designed to look for possible signs of life. These experiments discovered unexpected and
enigmatic chemical activity in the Martian soil, but provided no clear evidence for the presence of living
microorganisms in soil near the landing sites. According to scientists, Mars is self-sterilizing. They believe the
combination of solar ultraviolet radiation that saturates the surface, the extreme dryness of the soil and the
oxidizing nature of the soil chemistry prevent the formation of living organisms in the Martian soil.
The Viking mission was planned to continue for 90 days after landing. Each orbiter and lander operated far
beyond its design lifetime. Viking Orbiter 1 functioned until July 25, 1978, while Viking Orbiter 2 continued for four
years and 1,489 orbits of Mars, concluding its mission August 7, 1980. Because of the
variations in available sunlight, both landers were powered by radioisotope thermoelectric generators -- devices
that create electricity from heat given off by the natural decay of plutonium. That power source allowed long-term science investigations that otherwise would not have been possible.The last data from Viking Lander 2 arrived at
Earth on April 11, 1980. Viking Lander 1 made its final transmission to Earth November 11, 1982.
