Mars: A Century of Exploration
The Viking Missions
NASA's Viking Mission to Mars was composed of two spacecraft,
Viking 1 and Viking 2, each consisting of an orbiter and a lander.
The primary mission objectives were to obtain high resolution images
of the Martian surface, characterize the structure and composition of
the atmosphere and surface, and search for evidence of life. Viking 1
was launched on August 20, 1975 and arrived at Mars on June 19, 1976.
The first month of orbit was devoted to imaging the surface to find
appropriate landing sites for the Viking Landers.
On July 20, 1976
the Viking 1 Lander separated from the Orbiter and touched down at Chryse
Planitia. Viking 2 was launched September 9, 1975
and entered Mars orbit on August 7, 1976. The Viking 2 Lander touched
down at Utopia Planitia on September 3, 1976. The
Orbiters imaged the entire surface of Mars at a resolution of 150 to
300 meters, and selected areas at 8 meters. The lowest periapsis
altitude for both Orbiters was 300 km. The Viking 2 Orbiter was powered
down on July 25, 1978 after 706 orbits, and the Viking 1 Orbiter on August
17, 1980, after over 1400 orbits.
The Viking Landers transmitted
images of the surface, took surface samples and analyzed them for
composition and signs of life, studied atmospheric composition and
meteorology, and deployed seismometers. The Viking 2 Lander ended
communications on April 11, 1980, and the Viking 1 Lander on November 13,
1982, after transmitting over 1400 images of the two sites.
The results from the Viking experiments give our most complete
view of Mars to date.
Volcanoes, lava plains, immense canyons,
cratered areas, wind-formed features, and evidence of surface water
are apparent in the Orbiter images. The planet appears to be
divisible into two main regions, northern low plains and southern
cratered highlands. Superimposed on these regions are the Tharsis and
Elysium bulges, which are high-standing volcanic areas, and Valles
Marineris, a system of giant canyons near the equator.
The surface
material at both landing sites can best be characterized as iron-rich clay.
Measured temperatures at the landing sites ranged from 150 to 250 K,
with a variation over a given day of 35 to 50 K. Seasonal dust storms,
pressure changes, and transport of atmospheric gases between the polar
caps were observed, however the biology experiment produced no evidence of life
at either landing site.
Patches of white frost a few hundredths of a millimeter thick are visible
here. The frost is probably a mixture of water and carbon dioxide.
Here we see a combination of Viking 1 and
2 orbiter images
of the Candor Chasma part of Valles Marineris. The image is about 800
kilometers wide. Notice the erosional features.
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