NASA's Viking Project found a place in history when it became the first
U.S. mission to land a spacecraft successfully on the surface of Mars.
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.
Viking 2 launched 36 years ago today on Sept. 9, 1975. This artist's
concept depicts a Viking lander on the surface of Mars.
The
Viking 2 lander settled down at Utopia Planitia on Sept. 3, 1976, while
the Viking 1 Lander touched down on the western slope of Chryse Planitia
(the Plains of Gold) on July 20, 1976.
Besides taking
photographs and collecting other science data on the Red Planet's
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.
Although 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 Aug. 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 Nov. 11, 1982.
Image Credit: NASA/JPL-Caltech/University of Arizona