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The
Viking Project was begun by NASA on November 15, 1968,
and was composed of two orbiters and two landers. The
launch was initially planned for 1973, but this was later
changed to 1975 as the complexity and challenge of the
project became more apparent. The primary goal was to
determine whether life existed on Mars. The Viking mission
was a spectacular technological and scientific success.
Viking 1 was
launched on August 20, 1975, and arrived at Mars on June
19, 1976. The first month of orbit was devoted to photographing
the surface to find appropriate landing sites for the
Viking landers. On July 20, 1976, the Viking
1 lander separated from the Viking
1 orbiter and touched down at Chryse Planitia, the
Plains of Gold (22.48 degrees N, 49.97 degrees W).
Viking 2 was launched September 9, 1975, and entered Mars
orbit on August 7, 1976. The Viking
2 lander touched down at Utopia Planitia, the
Utopian Plains (47.97 degrees N, 225.74 degrees
W) on September 3, 1976.
The landing
sites were chosen primarily for their relatively flat
terrain to provide a safe landing spot for the two landers.
The Viking Orbiter 1 discovered that the original targeted
spots were too rugged and dangerous to risk landing on.
The orbiter searched for almost 3 weeks before finding
a new, more suitable landing site about 800 km west northwest
of the original site, but still within Chryse Planitia.
The orbiter took pictures of the proposed landing site
for the second lander. Almost half of the planet's
surface between 40 and 50 degrees north was photographed
in the attempt to find a suitable landing site for the
second lander in Utopia Planitia.
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biology experiments on the Viking 1 lander almost
failed due to a human oversight in programming the
computer. Just as the robot arm began to dig in
the Martian soil, the arm jammed. Using two replicas
of the lander, engineers duplicated the problem
and worked out a series of commands that succeeded
in freeing the arm. |
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The
Viking 2 landing was fraught with tension as an
orbiter malfunction shut down communications with
the Earth just after the lander separated. The lander's
computers had already been programmed for touchdown,
but the only way controllers could determine whether
it had landed safely was to monitor the data rate
coming from the lander via the low-gain antenna.
The time of touchdown passed and there was no increase
in data. Then, late by a few seconds, came
the increase in data. Within a few hours, engineers
had restored full communication with the orbiter.
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Searching
for life
The Viking landers were equipped with
three biology laboratories. The experiments included the
pyrolytic release experiment
which looked for microorganisms that, like plants photosynthesizing
on Earth, turn carbon gases in the air into carbon-based
organic molecules. The labeled release experiment
looked for evidence of organisms converting
food into energy and tissue, thereby releasing gases such
as carbon dioxide. The gas exchange experiment
looked for changes that Martian microbes
might cause in gas levels over long periods of time. (As
microbes metabolize, they consume and produce gases that
can be measured.) Water, nutrient and heat were added
to soil samples and the samples were analyzed. Although
a burst of oxygen came from the gas exchange experiment
and carbon dioxide was seen in the labeled release experiment,
it is believed that both results were caused by unusual
Martian soil chemistry. No supporting evidence of organic
material was found in any soil sample.
The Viking landers
were sent to the surface of Mars specifically to search
for chemical evidence of life. The results were both negative
and inconclusive. The weather instruments on the
landers determined that the coldest temperature was -85
degrees Celsius and the warmest temperature was -30 degrees
Celsius. (We now know that it gets colder and warmer at
other spots on the planet.) The wind speeds were about
11 mph with gusts up to 56 mph. Click
here for more information on the Viking lander life
experiments.
Mapping
the Surface
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Viking
Orbiters 1 and 2 mapped the Martian surface in great
detail. Photographs revealed that the valley networks
and flood channels were overlaid with impact craters
dating from the first two billion years of Martian
history. Volcanoes, lava plains, enormous canyons,
craters, wind-formed features, and evidence of surface
water are visible in the orbital images. The planet
appears to be divided into two main regions, the
northern low plains and the southern-cratered highlands.
Overlaid on these regions are the Tharsis and Elysium
bulges, which are high-standing volcanic areas,
and Valles Marineris, which is a system of giant
canyons near the equator. The surface material at
both landing sites can best be characterized as
iron-rich clay. |
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The Viking
2 orbiter was powered down on July 25, 1978,
after 706 orbits; and the Viking 1 orbiter was powered
down 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. Seasonal
dust storms, pressure changes, and transport of
atmospheric gases between the polar caps were observed.
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The
Face on Mars
In 1976, the Viking 1 orbiter photographed
a mountain about 1.5 kilometers across in the Cydonia
region of Mars. The mountain had a passing resemblance
to a human face. It appeared to be a wind-sculpted
mesa (a flat-topped mountain with steep sides).
It seemed to owe its face-like appearance to the
lighting conditions when the photograph was taken.
Some writers have popularized the notion that the
"face" was carved by intelligent beings. Photographs
taken of this mountain by the Mars Global Surveyor
spacecraft have shown that it is, after all, just
a mountain.
There
are several other images on Mars that have familiar
patterns. What do these look like to you?
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Questions
to think about:
- The Viking missions were not only successful but also
completely redundant; there were two of each orbiter
and each lander. What purpose did this redundancy
serve?
- What if one of the four spacecraft had been lost?
Would it have compromised the mission?
- How would you have decided where the landers should
be set down? What constraints would you have put on
the landing site criteria?
Next... Mars
Observer: The Lost Mission (pg. 5 of 12) |
