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National Aeronautics andSpace AdministrationJohn F. Kennedy Space CenterKennedy Space Center, Florida 32899AC 305 867-2468

KSC 169-80October 1980EXPLORATION F A RUSTYPLANET

First photograph ever taken on the surface of Mars, obtained minutes after the historic toudldownof Viking Lander 1. Note the dust particles that settled Into the concaw center of the space-craft's footpad upon landing.

On the lonely plains of a small planet, millions of miles from Earth,stand two relics of one of the most monumental expeditions in the history ofmankind. They are named Viking landers, because like the Norse explorers ofold, they set out across a wide and landless void to seek a new world.They look like metallic three-legged creatures, but the landers arereally miniature robot laboratories whose main purpose was to probe for life

in the red soil of Mars. There are four Viking components in the vicinity--two orbiters circling the planet (both now inactive) and two landers on thesurface (one retired, the other still working once a week and hibernating therest of the time).They came to the red planet in the summer of 1976 as two doublespacecraft. each with a lander and orbiter temporarily attached. On July 20,; the Viking 1 lander separated from its orbiter, parachuted through the thin.atmosphere. fired retrorockets, and touched down in a swirling cloud of dust.This was. to the day. 7 years after astronauts first landed on the Moon.

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Almost immediately the first data was transmitted back to Earth, that theMartian surface was strong enough to support a heavy machine. Then came thelong-awaited first photograph, a very clear black-and-white picture of theground below and one of the Viking's footpads. It took 5 minutes of camerascanning to produce the historic photo, and 20 minutes to transmit it morethan 321 million kilometers (200 million miles) back to Earth.

The next photograph, a panorama of the Plains of Chryse surrounding theViking 1 lander, revealed a gently rolling plain with fine soil and rocks ofall sizes strewn abundantly in every direction. Later photographs showed thecolor of the rocks ranged from light to dark grey to slightly reddish and thatthe soil was rust-red. Some rocks contained small holes, which resembled thesponge1ike texture of lava from Earth volcanoes. Some scientists think theywere formed the same way, by gases bubbling through molten rock. Others, how-ever, believe the pits were carved by wind and soil action, like simi1ar-looking rocks in the Egyptian desert. The Viking 1 lander also photographedrippled dunes, evidence that the wind does indeed shape Martian landforms.Photographs from the Plains of Utopia, where the Viking 2 lander toucheddown on September 3,1976, were similar.The lander pictures surprised scientists who expected the Martian sky toappear deep blue to black. Colored by fine-grained red dust suspended in theatmosphere, the sky had a creamy-pinkish hue.Though one project scientist said the scenery was so much like an Earthdesert that he almost expected to see camels, the Viking cameras detected nosigns of living creatures in their vicinity. But because Martian life couldexist at microscopic sizes--as most life on Earth does--the true tests wereperformed on the molecular level. The twin landers performed three different

life detection experiments in search of carbon-based life forms such as thoseon Earth. The carbon atom is the core of every living molecule on Earth.The pyrolytic release experiment began with a soil sample scooped up fromthe windblown surface and dumped into an incubation chamber on the lander.Radioactive carbon dioxide was added to the atmosphere in the chamber, Martiansunlight was simulated, and the sample was heated to 625C (1,150F) to driveoff organic vapors. If any Martian organism converted the carbon dioxide intoorganic compounds, the compounds could be detected by their radioactivity.Small amounts of carbon dioxide were converted into carbon compounds at bothlander sites, mimicking biological activity, but this could have beenaccomplished by a reducing agent in the soil, such as metallic iron.The labeled release experiment fed radioactivity-tagged nutrients to asoil sample, and monitored its activity. An initial, rapid release of radio-active carbon dioxide (at both lander sites) indicated metabolic activity, butthe reaction slowed down, suggesting instead that some chemical was being used

up.The gas exchange experiment exposed soil to a nutrient. Samples of theatmosphere above were periodically examined in a gas chromatograph, whichsearched for gases of low molecular weight, such as hydrogen, carbon dioxide,

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methane, or nitrogen. Their existence would mean a microbial feast hadoccurred. Unexpected, large bursts of oxygen occurred at Chryse, less atUtopia, which could be explained as the result of chemical rather than biolog-ical activity. Had hydrogen or methane gas been detected as well, thepresence of life would have been substantiated.The test results were ambiguous, although forms of activity were defin-itely observed. It was impossible to tell if the activity detected in theMartian soil were some form of unusual chemistry or a specialized and uniqueform of life. The unending blasts of ultraviolet radiation that penetrate thethin Martian atmosphere may have created chemical reactions so exotic they canmimic biological reactions.An X-ray fluorescence instrument characterized the elements in soilsamples at both Viking landing sites, and showed that although 5,000kilometers (3,100 miles) apart, the two sites have approximately the same soilcomposition. The chief elements are: oxygen, 42 percent; silicon, 21percent; and iron, 13 percent. Aluminum, magnesium, calcium, sulfur,

chlorine, titanium, and potassium constitute another 16 percent of the total.Elements in the remaining 8 percent are probably undetectable by this method.The long-held theory that the reddish-ochre Martian surface is a red ironoxide was confirmed.In the days that followed the Viking landings, each spacecraft's meteoro-logical boom unfurled and began sending weather data from Mars. As daysturned into weeks, the weather remained almost unchanged. At Chryse tempera-ture highs were about -28C (-19F) each day, and lows about -82C (-116F).At Utopia, temperatures ranged from highs of about -31C (-23F) to lows aboutthe same as at Chryse. Wind speeds averaged 23.3 kilometers per hour (14.5miles per hour) at Chryse, and 12.5 km/h (7.8 mi/h) at Utopia.The highest atmospheric temperature ever recorded by the landers, -21C(-17F), occurred at Chryse (the southern site) in midsummer. The lowest,-124C (-191F), was measured at Utopia (the northern site) in winter. Thiswas approximately the freezing point of carbon dioxide. Wind speeds gusted to120 km/h (74 mi/h) during two global dust storms that occurred in the firstyear the Vikings spent on Mars. The pressure of the atmosphere varied from6.8 to 9.0 millibars at Chryse, as weather systems swept by the Viking 1lander.The only optical change observed by the landers during the storms was asubtle darkening of the the skies. However, during the next winter the Vikingcameras photographed patches of receding frost at the Lander 2 site. Afterthe frost disappeared when the weather grew warmer, a thin layer of 1ight-

colored dust was detected covering the soil and rocks at the same site. Thefrost, probably water ice, most likely condensed around the nuclei of dustparticles that slowly settled out from the global dust storms that ragedearlier in the year.The landers determined the composition of the atmosphere as theydescended, and then on the surface: carbon dioxide, 95 percent (compared to0.03 percent of Earth1s); nitrogen, 2-3 percent; oxygen, 0.1-0.4 percent;argon 1-2 percent; and traces of krypton and xenon.

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Circling above the planet, the orbiters found the air of Mars to containonly about 1/1000 as much water vapor as that of Earth. The atmospheric pres-sure is only about 1/125 that of Earth's, but on both planets the temperaturereaches its peak at about 3 p.m. local time.Mars nas fewer CloudS tnan tne tartn, but a large variety: summer

cyclones, wave clouds, surface hazes, and huge cloud systems that cover thenorthern pole and the flanks of the great Martian volcanoes.Ine orblters proVlded nlgn resolutlon pnotograpns of mysterious geo-graphic features. There are icy polar caps with laminated deposits; thelargest dune field in the solar system; sinuous dry channels, perhaps water-cut in an earlier time; and meteorite craters with scalloped ejecta, some withteardrop-shaped deposits trailing behind them. There are gargantuanvolcanoes. Olympus Mons, the largest volcano on Mars, is about 600 km (375miles) across at the base and approximately 25 km (15 miles) high. There isalso a great network of canyons called Valles Marineris, which extends 4,500km (2,800 miles) in the equatorial regions of Mars.Ine vlKlng expealtlons nave answered many questlons about Mars, whi Ieraising others, but the major question--Is there life on Mars?--remainsunresolved. Perhaps future spacecraft can unlock the remaining secrets of thered planet.

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