Mars Exploring The Planets Mars

Viking Lander Diagram

  Numerous experiments designed to photograph, probe, and sample the Martian surface were packed into the 600-kilogram (1,300-pound) Viking Lander. Each Lander was powered by two radioisotope thermoelectric generators, which convert heat to electricity from the radioactive decay of Plutonium 238. The Landers require 70 watts of power, less than that needed by most light bulbs.


A View of the Surface

Viking Camera

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Smithsonian Institution photograph.

Each Viking Lander is equipped with two identical cameras that, unlike conventional cameras, do not use film. Instead, a moveable mirror scans a vertical segment of the Martian scene, and photodetectors record the amount of light reflected into the camera. A complete picture, or "image", of the surface is made by completing a vertical scan and then rotating the camera slightly for the next scan.

During the first three months of the Viking Primary Mission, more than 1,500 individual pictures of the surface were relayed to Earth by the Landers. Following this initial flurry of activity, selected images have been taken to note changes due to seasons and dust storm activity.

First View from The Surface of Mars

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NASA photograph

Shown here is the first picture from the surface of Mars, taken by Viking Lander 1 on July 20, 1976. The dark vertical streaks on the left side of the image were caused by dust settling out of the atmosphere from disturbance by the Landers' retro-engines.

Life on Mars?

In addition to searching the landscape for large features with the Lander cameras, three types of experiments were carried out to determine whether the Martian soil contains any form of microscopic life. The Landers performed each of these experiments repeatedly on different samples of soil using the Viking Lander soil sampler shown at right. No conclusive evidence for life on Mars was found during the Viking missions.

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Viking soil sampler
Smithsonian Institution photograph

The first of the biology experiments, the Gas Exchange Experiment, was designed to test whether minute organisms lying dormant in the soil would come to life after addition of water or organic compounds. Both oxygen and carbon dioxide were given off after addition of water, but their release could have been caused by decomposition of the soil.

The second experiment, the Carbon Assimilation Experiment, assumed that organisms would thrive in the carbon dioxide-rich atmosphere of Mars, and would incorporate or assimilate carbon from the atmosphere in their life processes. Although some carbon compounds were produced during this experiment, they could also have been caused by chemical reactions in the soil.

The third experiment, the Labeled Release Experiment, tested whether life processes were present by monitoring the release of radioactive gas introduced to the sample in the form of nutrients. A rapid release of carbon dioxide occurred after the first addition of nutrients, consistent with biological activity. However, the amount of carbon dioxide soon diminished, suggesting that Martian organisms were not responsible.

Viking Tests for Life in Soil Samples
A trench in the Martian surface shows the location of the first sample analyzed for signs of life. Later samples were taken from beneath the thin crust of the surface and from beneath rocks.

Although Viking life experiments were inconclusive, the search for evidence of ancient organisms remains a primary research objective and future spacecraft exploration of Mars will be designed to assess the habitability of the Red Planet.


The Weather Report
Like a weather station on Earth, the Viking meteorology experiment measured the atmospheric pressure and temperature, and the wind speed and direction. Both the temperature and wind sensors are mounted on a boom, which extends away from the spacecraft so that wind direction is not be affected by the Lander.

Continuous weather measurements were made during the first three months of the mission. These detailed records showed that the atmospheric pressure was about 7 millibars during the Martian summer, or about 0.007 times the atmospheric pressure on Earth. The mean temperature during the summer was -58 degrees C (-72 degrees F), and wind gusts up to 65 kilometers per hour (40 mph) were measured.

Extension of the mission beyond the original three months allowed measurements of seasonal changes at both Lander sites. During the first winter at the Lander 2 site, temperatures dipped to -113 degrees C (-171 degrees F).

Vikings' measurements were used for comparison purposes during the Mars Pathfinder mission.

Surface Composition

To determine the composition of the atmosphere, and whether organic molecules exist in the surface samples, a Gas Chromatograph Mass Spectrometer measured the atomic composition of gas samples from heated soil and the atmosphere. No organic molecules were detected at either landing site, but the abundance of the gas argon (36AR) was found to be less than that expected. This difference suggests that during the early evolution of the planet, the amount of gas released to the atmosphere of Mars was less than that released to the atmosphere of the early Earth.

The composition of heavier elements, those that are common in rocks and soils, is determined by means of an X-ray Fluorescence Spectrometer. Samples of Mars are dropped into the instrument in the Lander body, where they are exposed to high-energy x-rays. Each element then produces its own characteristic x-rays, which are counted and recorded. Following the analysis, the sample is dropped out of the bottom of the test container so a new sample can be measured.

Analysis of the surface soil indicates that both landing sites are similar in composition and primarily composed of the elements silicon and iron. The sulfur content is unexpectedly high, and might be caused by water-soluble minerals deposited on the surface. Lander soils could be derived from weathering of an iron-rich igneous rock, such as basalt. Consistent with these analyses, magnetic particles were photographed clinging to the magnets on the sampling arm and on the camera reference chart.


Other Results

The Viking spacecraft far exceeded all goals set for the mission and provided scientific data needed to answer many of our questions about the red planet. A seismometer aboard Lander 2 indicated that the planet is presently very stable; a similar instrument on Lander 1 failed to operate. Measurements of motor currents needed to move the soil confirmed the appearance of a crusty surface, or "duricrust," that is more cohesive than loose sand.

During the Radio Science Experiment, as Mars passed behind the Sun, the most accurate measurement of interplanetary distance was made. The 321,000,000-kilometer (200,000,000 mile) distance between Earth and Mars was measured to an accuracy of 1.5 meters (5 feet), and the delay in radio signal due to the Sun's gravity was exactly that predicted by Einstein's General Theory of Relativity--0.0002 seconds.

Touchdown on Mars || Laboratory on Mars || Deep Space Network || Viking Lander Views
The Viking Mission

Exploring The Planets