Viking probes

(redirected from Viking program)
Also found in: Wikipedia.

Viking probes

(vÿ -king) Two identical American spacecraft, each comprising an Orbiter and a Lander, that were launched in 1975 on a mission to search for life on Mars. Each Orbiter weighed 2325 kg and carried two television cameras to photograph the surfaces of Mars and its satellites, and instruments to map atmospheric water vapor and surface temperature variations; 52 000 pictures were relayed to Earth. After detaching from its Orbiter, each Lander, weighing 1067 kg, made a successful landing using a combination of aerodynamic braking, parachute descent, and retro-assisted touchdown. The Viking 1 Lander set down on July 20 1976 in Chryse Planitia after a delay while Orbiter photographs were searched for a smooth landing area. Viking 2 landed on Sept. 3 1976 in Utopia Planitia, 7420 km northeast of the Viking 1 Lander.

Each Lander carried two television cameras, a meteorological station, a seismometer, and a set of soil-analysis experiments serviced by a sampling arm. Only the seismometer carried by Viking 1 failed to function; that on Viking 2 registered mainly wind vibrations and a few minor Martian ‘earth’ tremors. The television cameras returned views of a red rock-strewn surface under a pink dusty sky. Sand or dust dunes were evident at the Viking 1 site but no life forms were seen. The meteorology instruments reported temperatures varying between 190 K and 240 K with mainly light winds gusting to 50 km per hour.

X-ray analysis of soil samples showed a high proportion of silicon and iron, with smaller amounts of magnesium, aluminum, sulfur, cerium, calcium, and titanium. Gas chromatograph mass spectrometers carried by the Landers failed to detect any biological compounds in the Martian soil, but more ambiguous results were returned by three experiments designed to test for microorganisms in various soil samples.

A labeled-release experiment tested for radioactive gases that might have been expelled from organisms in a soil sample fed with a radioactive nutrient. In a pyrolytic-release experiment soil was placed with gases containing the radioactive isotope carbon–14. The idea was that Martian organisms might assimilate the isotope into their cell structure in a process similar to earthly photosynthesis. Later the soil was baked and a test made for the carbon isotope in gases driven off. Finally, a gas exchange experiment monitored the composition of gases above a soil sample, which might or might not have been fed with a nutrient. If Martian organisms were breathing the gases, a change in composition might be detected.

In practice, the pyrolytic release experiment produced negative results, while the gas exchange experiment gave a marginally positive response, which could be explained in terms of a chemical reaction involving the soil and nutrient. The positive response of the labeled-release experiment was marked but disappeared when the soil was sterilized by preheating.

Detailed analysis of the Viking Lander experiments led to the conclusion that there is no form of life on Mars.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006
References in periodicals archive ?
"With an ocean cruise, it's the ship itself, said Nikolas Rabogliatti, the Viking program director.
No probe since NASA's Viking program in the late 1970s has explicitly searched for extraterrestrial life -- that is, for actual living organisms.
Mass spectrometry has previously been used to analyze Martian soil for the first time as part of NASA's Viking program in the 1970s.
What's the connection between a Roman legionnaire, medieval art and the much earlier Viking program? It all goes back to the Higgins Armory Museum in Worcester, where Mr.
Phoenix was the sixth spacecraft to successfully land on Mars since robot exploration of the planet's surface began in the 1970s with the Viking program.
Information on Martian atmospheric gas was transmitted back to Earth in 1976 by unmanned vehicles that landed on the planet during NASA's Viking program.
You'll read of the creative force within you waiting to be tapped--Chuck Taylor, who at age 40, out of a job and with a family to support, tapped into the creative force to form a new company that contributed 44 different parts to NASA's Viking Program.
Previous samples from the Martian atmosphere were analyzed three decades ago during NASA's Viking program.