the viking mission

8/8/2019 The Viking Mission

1/12

An Educational Publicationof theNational Aeronautics andSpace AdministrationOne of a series of NASA Facts about the explorationof Mars.NF-62/6-75

.Obtain information to improve our understandingof how Earth developed as a planet able to supportlife and how we can bette;rpreserve and protect theenvironment of Earth. !If Viking d~tects life 01\ Mars we might expectthat among the hundred billion stars in the Galaxy,many of which have planets, there may be other solarsystems hat also have life and possibly have developedintelligent life forms.The Viking s,pacecraft re designed o make threebasic types of scientific observations of Mars. First, theorbiting spacecraftwill continue with the detailed photo-.Seek evidence of whether life exists now or hasexisted in the past on Mars.

1

Mission to Land on MarsThe American bicentennial Viking mission to Marsconsists of two unmanned NASA spacecraft aunchedin Aug. and Sept. 1975. When each spacecraft reachesMars during the summer of 1976 it will go into orbitaround the red planet and later dispatch a landing cap-sule to the Martian surface. Each lander and orbiter willcarry a payload of scientific instruments aimed at twomajor scientific explorations of our neighbor world:


2/12

Each spacecraft ravels through space or almost ayear and arrives at Mars when he planet s on the oppo-site side of the Sun from the Earth, having traveledsome 644 million kilometers (400 million mi.) to reacthe Red Planet. At the rendezvous distance of 322million kilometers (200 million mi.) radio signatraveling at 300,000 kilometers per second (186,000mps) take 20 minutes to travel from the spacecraft o

The five phases of the Viking mission to Mars are identifiedon this diagram-Launch, Cruise, Orbit, Landing and SurfaceOperations. If the Viking spacecraft survive beyond solarconjunction in November 1976. there will be a sixth, extended,phase of Viking operations. '"Bioshield CJettison

survey of the planet started by earlier Mariner space-craft. Second, the nuclear-powered lander will searchfor forms of life on the surface. Third, both spacecraftwill obtain information about the physical features andmakeup of the planet and its atmosphere.The orbiters and the landers will conduct theirexperiments to study surface geology and the internalstructure of Mars, and to find out if Mars is stillgeologically alive. Orbiter and lander photographs willidentify types of land forms, stratification, folds, joints,faults, rock types, erosion, sedimentsand soil, and willprovide clues about mineral and chemical compositionof the Martian surface. If marsquakes are recorded asexpected, scientists might be able to determine if Marshas a core, a mantle, and a crust, as does the Earth.Thus they will be able to compare the internal struc-tures of Earth, Moon, and Mars through actual seismicrecordings.The lander instruments will identify elements andminerals in the soil. Thermal mapping from orbit willsearch or ground frost and thermal hot spots that mightindicate heat flow anomalies, such as volcanoes, whereinternal heat comes to the surface of the planet.Viking's radio and radar systems will provide in-formation that should improve our knowledge of Mars'size, mass, gravitational field, surface density, andelectromagneticproperties, and atmospheric density andturbulence. The orbiters will also observe he formationand movement of clouds on Mars, watching the grossmeteorology of the plant from orbit, while the landerssample ground-based weather at two positions on theplanet's surface.

CentDefle'1 Stage2I Separation

Shroud/ JettisonStage1Separation

The Viking ProjectSolid RocketMotor Separation

The Spacecraft and their PathsViking is the most complex space mission to be flownby NASA, since it requires the simultaneous operationof four sophisticated spacecraftaround a distant planet,each of the spacecraft carrying out exacting scientificexperiments on or about an alien world. It is the firstAmerican mission to land a spacecraft on anotherplanet.

launchTitan III/Centaur

2

Centaur BurnParking Orbit,

The Viking project of the National Aeronautics andSpace Administration is managed by the Langley Re-search Center at Hampton, Virginia. Martin MariettaCorporation designed and built the landers, is re-sponsible for developing the science instruments, andbuilds the Titan III launch vehicle. NASA's Jet Propul-sion Laboratory is responsible for building the or-biters and for providing the facilities for spacecrafttracking and for mission control Eighty scientists ofthe United States and other nations direct the scientificinvestigations of this project. They form thirteen scienceteams.


3/12

some on-course corrections to the flight path to makesure that arrival is timed just right to enter the requiredorbit around Mars.Next, when the spacecraftenters ts elliptical patharound Mars, the mission moves nto the orbital phaseof operations. Cameras aboard the orbiter photographthe landing sites; the orbit is adjusted as needed,and allis made ready for the descentof the landing capsule.An entry phase follows in which the landing cap-sule goes through a series of complex sequentialopera-tions, deceleration from orbit by rocket braking, entryinto the atmosphere and braking by atmospheric drag

Earth, and commands to the spacecraft also take thesame ime to reach it from Earth.The diagram shows he five major operationsof theViking mission. The launch phase s accomplishedwhenthe Titan III/Centaur launch vehicle lifts the spacecraftfrom the pad at the Air Force Eastern Test Range,Florida, and places it into orbit around the Earth. Ashort while later the rocket engines of Centaur againthrust and send the spacecraft nto an elliptical solarorbit to carry it from Earth to Mars.The cruise phase of Viking operations is a periodof waiting on the long voyage to Mars, punctuated by


4/12


5/12

of Martian soil and deposits them into the maw of themachine like some strange animal scooping up food.The soil samples are not, however, food for this Earthmonster invading the Red Planet. They are samplesfor complex mini-laboratories inside the lander, thereto be analyzed and bathed in nutrients to see if anyMartian life within them can be cultivated into activitythat will reveal its presence.For several weeks after touchdown each landerwill gather samples, take photographs, record weatherconditions, and analyze the atmosphere of the RedPlanet. All the while the orbiters aloft will be keepingwatch on their offspring below, accepting their data andrelaying it back to Earth.But gradually and inexorably the motion of Earthand Mars will carry Mars behind the Sun as seen romEarth and communication will be broken during No-vember 1976. Before this happens, he landers will beplaced into hibernation. When the planet emergesagainfrom behind the Sun, the landers can be brought outof hibernation and continue their experiments on the

surface of Mars.This would be an extended mission since thenominal Viking mission ends at the time of solar con-junction. In recent years all NASA spacecrafthave sur-vived their nominal missions and continued into ex-tended missions,and Viking is expected o do the same.

cause he lander to fall toward Mars. About two hoursafter separation, the lander encounters the Martianatmosphereand uses ts aeroshell o protect it from theheat of entry into this atmosphere.This shell also slowsthe capsule down by dissipating energy into the at-mosphere. When the lander is about 6200 meters(20,000 ft.) above the surface of Mars a parachute isdeployed to slow the descent urther. The aeroshell sblown off and falls away from the slowly descendinglander. At about 1200 meters (4000 ft.) above thesurface, the rocket engines of the lander ignite andbrake the fall further, ultimately bringing the spacecraftsoftly to rest on the surface of Mars. As soon as thefootpads touch down, the rocket engines are turned off.For these maneuvers he lander has to be a very com-plex spacecraftable to perform them all automatically.But once it is down on the surface ts operations changeto a highly sophisticated machine for exploring thesurface of Mars. Now it sets on three spindly legs,its instruments whirring, its dish-shaped antennapointed skyward, its two cameras urning and blinkingas they build up detailed strip pictures of the Martianpanorama.On top of the lander at either side are two radio-isotope-powered electricity generators for its powerneeds. And stretching out in front, between the twocamera turrets, is a long arm which scoops up samples

Diagram of the orbiter spacecraft of Project Viking withlander attached in cruise mode.

r Propulsion, ModuleLow Gain Antenna ~ / -\:::: Solar~anel-.1' ..d~~~~~~::;::::;:~ -

,

~~

r~

Science Platform

~-~"""ruise Sun Sensor & Sun Gate~ I

Thermal Mapper (IRTM)-==::::=~~:::

Imaging sYstem ; ;~~VI~;~~< ~ater Vapor Detector c" ~(MAWD) ~.,

- '- Radio ScienceHigh GainAntenna

L VikingOrbiterL Relay ntenna Attitude Control-JGasJets-- Viking lander Capsule

.Solar EnergyController

-Orbiter Bus


6/12

The lander spacecraft on the surface of Mars searches forevidence of Martian life; it samples the soil and theatmosphere, and photographs the surrounding area.

The first Viking will be aimed for a landing siteat 19.5 degrees north latitude and 34 degrees westlongitude, in a region of Mars called Chryse. This isprime site A. Chryse means "land of gold," and relatesin ancient Greece to a golden land in the far east Inmythology Chryse was a priest of Apollo whose daugh-ter was seized in the battle of Troy and given to Aga-memnon, only to be returned after Apollo struck theGreek camp with a plague.The southern half of the Chryse area consistsmostly of deeply dissected plateaus, possibly depositedfrom volcanoes. But much material from this areaseems o have been swept northward along well-definedchannels to a low area of only slight relief where it isintended to land the Viking lander. Scientists believethat the surface at this site is nearly everywhere par-tially covered by dust deposits ransported by the wind.There may also be material washed from the canyonsand interspersed with the dust layers. The wind-drivendeposits may consist of sand dunes, each hundreds of

Where the Vikings will land on MarsFollowing months of study by a panel of geologists andother scientists:four sites were selected on Mars for thelanding of the two Viking spacecraft. These sites wereselectedon the basis that they must be geologically dif-ferent to provide two types of Martian surface sampling,must provide unobstructed areas for meteorology, andbe at low altitude where atmospheric pressure s great-est and there would be a chance of liquid water. Addi-tionally the sites were chosen on 'river' deltas and nottoo widely separatedso that the two Viking landers canmake seismographic observations of the same mars-quakes.In addition, the sites had to be between 25 de-grees south latitude and 75 degrees north latitude atlocations where there would be only gentle slopes withno large protuberances and no surface rocks, andwhere winds might blow at less than 70 meters persecond (220 f.p.s.).


7/12

meters across and covered with tiny ripples. The chan-nel deposits might consist of slightly rolling hills withsmall channels and low sandbanks, each perhaps tensof meters wide. This site is within a region where watermay have flowed in copious quantities in the past.

Landing sites chosen for the two Viking spacecraft. Eachconsists of a prime site and a backup site as shown on thismap of the planet. Close-ups of each landing site are shownabove and left. Prime A in Chryse and Prime B in Cydonia.The long ellipses signify the areas in which the Vikingsmight land.Viking landing sites.

,.


8/12

action when it reaches he surface, could be damagingduring the lander's des.ent.With the lander safely down, the orbiter's cameraswill then be used for routine mapping of Mars to sup-plement the pictures returned by Mariner 9 in 1971and look for significant changeson Mars since that date.As far as s known at present, ife must have waterfor its survival. Consequently, n searching for life onMars, landing at siteswhere water might be in the liquidstate is very important. The orbiter will carry an at-mospheric water detector that will scan the selectedlanding sites to see f there are concentrations of watervapor in the atmosphere above them. After the landeris safely down, this instrument will look at other re-gions of Mars to map their water vapor characteristics.Since life, too, on cold Mars might be predisposedto seekwarm spots on the generally nhospitable planet,a search will be made from orbit for warmer regions inthe vicinity of the landing sites. The instrument usesinfrared measuring devices at various wavelengthsableto detect small areas of Mars that are as little as onedegree hotter or colder than their surroundings.

The Science Experiments -LandersMost of the science instruments are carried in thelanders,which will not only sample the surface but also

The second Viking will be targeted to land farthernorth in an area called Cydonia, a flat stretch of thenorthern basin plains where water may be availableeven today. Cydonia is the nam~ of a town in Cretewhich, in turn, is named for Kydon, the son of thegreatestking of Crete, Minos.The landing site area consists of smooth andmottled rolling plains; possibly flows of basalt coveredby wind-borne debris, volcanic dust, and water-bornesediments. The site is located on the eastern side ofthe Mare Acidalium where the plains units of the Mar-tian northern lowlands abut the higher equatorial pla-teaus and hills. There may be volcanic cones and lavaflows in the area, as well as the wind-borne and water-borne debris.There is a band around Mars between latitudes40 and 55 degrees north at which some parts of thesurface are depressed ike the floor of some ancientdried up ocean. In this band liquid water may be pres-ent for about two or three weeks during each northernspring. Thus life might flourish for a brief period hereeach Martian year, taking up its water from the Martiansoil as permafrost melts into liquid. To a single bac~terium a drop of water is as good as an ocean. Thissecond anding site, known as prime site B, is locatedin this band at 44.3 degrees north latitude and 10 de-grees west longitude.Both prime sites have backup sites to be used ifthe first sites are rejected following close observationsfrom orbit before the actual landings. The backup tosite A is in a region known as Tritonis Lacus at 20degreesnorth latitude and 252 degreeswest longitude.The site B backup is in the region of Alba at 44.2degrees north latitude and 110 degrees west longitude.All the sites are thus in a variety of plains in the north-ern lowlands comparable to the Earth's ocean floorbasins, close to the margins of the Martian continentsThe A sites are where the highlands drained, so sam-ples there should provide regional highland material.The B sites are on ocean floor sediments.This com-bination gives the best possibilities for fossil andpresent water and best samples o test current theoriesabout the evolution of Mars.

Orbitershe Science ExperimentsEach orbiter carries two television cameras which atclosest approach o Mars on each orbit (periapsis) willprovide pictures of the surface sufficiently detailed toreveal an object the size of a football stadium. A majoreffort will be to check the landing sites chosen or theViking landers before these anders are sent down fromorbit to the Martian surface.Scientists on Earth will interpret the pictures geo-logically to try to ensure that the exact ~anding siteschosen will be in a relatively flat area rather than inhilly or rough country. The orbiter will also be alertfor local dust storms that might be developing beforethe lander is sent from orbit to the surface. Such astorm, while it is not expected o put the lander out of


9/12

make direct measurementsof the Martian atmosphereon the way down to the surface.Some atmospheric measurementshave been madepreviously by Soviet spacecraftentering the atmosphereof Mars, and by both U.S. and Soviet orbiting andflyby spacecraft. The surprise to scientists was that theatmosphere of Mars is very deficient in nitrogen com-pared with that of Earth. Some of the Soviet experi-ments imply that there might be quantities of anotherinert gas such as argon; as much as one-third of theMartian atmosphere.Two entry experimentswill be made by the lander.The first is for the highest regions of the atmosphereknown as the ionosphere,where atmospheric moleculeslose electrons under he influence of solar radiation, andbecome ionized. Earlier Mariners passed radio wavesthrough the upper atmosphereof Mars and detected hisionosphereat a height of about 130 kilometers (81 mi.).The Viking landers will use an instrument called aretarding potential analyzer which measures the con-centration and charge of ions and the concentration ofelectrons in the ionosphere as they flow across the in-strument's wire grids. Charged particles of different en-ergies and electrical charges are filtered and measured.But the gases n the atmosphereof Mars are mostlyun-ionized, i.e. electrically neutral. A separate instru-ment is carried to determine the identities and concen-trations of the uncharged atmospheric gases. This in-

strument is a mass spectrometer which must rapidlyanalyze the gases lowing through it as the aeroshell ofthe lander pushes through the atmosphere. Every fiveseconds he instrument will search through a range ofatomic particles including hydrogen (atomic mass 1)and carbon dioxide (atomic mass 44). This range in-cludes those other gasesexpected in the Mars atmos-phere.The physical characteristics of the Martian at-mosphere will also be measured during the landingphase by several other sensorscarried on the aeroshelland the lander itself. Measurements will be made ofhow quickly the atmosphereslows down the lander. Thepressure and temperature of the atmosphere at variousheights will be measured along the landing track.But the main scienceexperiments begin when thelander has safely reached he dry, dusty surface of Mars.Two cameras, mounted on extensions above the uppersurface of the lander, will take 360 degree panoramicviews of the landing site. The two cameraspermit three-dimensional (stereo)views of the surface of Mars. Thesecameras are the facsimile type which use nodding mir-rors to make a picture by scanning the scene to bephotographed in a series of very narrow vertical strips.Each camera requires 20 minutes to scan a full scene;so a rapidly moving object would not be photographedon Mars. However, the cameras do not require a lens(that might be scoured by Martian dust storms) and

This photograph of sand dunes in a western desert of theUnited States was taken with a Viking lander camera. It

shows the type of detail that is expected to be revealedby Viking when it returns photographs from Mars in 1976.


10/12

they show objects in sharp focus from close to thelander to the far horizon. They are adapted to takephotographs n black and white, full color, and infrared.A picture of terrestrial sand dunes taken with one ofthese camerasshows the tremendous detail expected tobe revealed on the Martian landscape.The pictures of Mars will provide geologists withinformation to help interpret what has been happeningon Mars since the water flowed in the ancient channelsperhaps hundreds of thousands of years ago. Water-worn debris might be revealed that will confirm flowsof surfacewater. The cameras will also reveal any vege-tation that might be growing on the surface. Note thatMartian plants could be brown or black since theymight use other sunlight absorbers than the chlorophylthat gives the green color to Earth's plants. Views ofthe footpads of Viking resting on the Martian dust willallow scientists o determine the strength of the Martiansoil and possibly its composition.Suppose you could stand on the dusty landscapeof Mars on July 4, 1976, beneath the dark blue skywith its feathery wisps of high cirrus clouds. In thebroad valley where mountains of soil were spread even"ly in past ages by water deluging from the equatorialcanyonlands you might see a distant dust devil whirling

across the sand dunes. And squatting on the Martiansoil would be the Viking lander moving its mechanicalappendages.The faint 'whirr of electric motors wouldstruggle through the thin cold air as a slender arm ex-tends in front of the lander and carefully scoops up asample of soil in its mechanical claw. The arm thenretracts and drops the sample into round openings inthe top of the lander.The search or life on Mars will have started. Thelander carries three major life detection experimentswhich test for photosynthesis (the basic process of ter-restrial plant life), for metabolic activity (consumptionof nutrients), and for respiration (interchange of gaseswith the atmosphere).In an instrument occupying a single cubic foot ofvolume, each ander packs the equivalent of three auto-mated biochemical laboratories, a computer, ovens,radioactivity counters, a sunlamp, and a gas chromato-graph. It has 43 miniature valves to control flow of gasand nutrients, 40 temperature control devices, 22,000transistors, and 18,000 other electronic parts.A simple drawing of the biology-package s shown.The first experiment deals with photosynthesis, thebasic process by which plants apply energy fromthe Sun to assimilate carbon from the atmosphere

Biology experimentThis diagram shows the three life detection experimentsthat Viking will make on the surface of Mars; a) checking for photosynthesis; b) checking for conversion of nutrients,and c) checking for respiration.

Soil Sample

DU~licateoControl nalysisLabeledNutrientMedium0

NutrientMediumCLightSourcearbonDioxide QLabeled)

Sampleyrolysis

Column

DetectorFor C14

DetectorFor C 14

PhotosyntheticAnalysis Metabolic Analysis Metabolic Process


11/12

and their concentrations, not how they are compoundedinto molecular substances.But a good understanding ofthe surface materials may be obtained by camera ob-servations of how the clay/-like sampler scoops up thesoil and how the landing legs disturb this soil. A mag-net on the scoop will also reveal the presence of mag-netic materials in the Martian soil.The presence of large volcanoes on Mars raisesthe question of whether they are still active. Volcanoeson Earth often lie dormant for centuries. But dormantvolcanoes can still give rise to marsquakes.Each Vikinglander carries a seismometer o detect such quakes andsearch or evidenceof a Martian core. The seismometerwould also detect he footstepsof a large animal passingby the lander!Another group of the lander's instruments will re-cord Martian weather as weather stations do on Earth.Pressure, emperature and wind velocity will be record-ed. The atmosphere will also be analyzed for its com-position by means of amass-spectrometer. It will de-termine how the atmosphere hangeseach day for manyMartian days. Then the instrument will be used inconjunction with an oven that will roast soil samplesso that they give off in sequence ases hat can be recog-nized as originating from organic molecules.The next booklet in this series describes he se-quence n which theseexperiments will be made in orbitand on Mars during the mission of the two Vikingspacecraft-the orbiters and the landers.

STUDENT PROJECTSProject One-Role PlayingYou are the leader of the Martian community. Bymonitoring Earth TV, even though you do not under-stand Earth languages, you have seen that Viking iscoming to your planet and what it will do; i.e. photo-graphs from orbit, photographs from the surface, ifedetection, seismometry. You and your subjects, theclass, must decide if and how you will make yourselvesknown to the Earthmen through their spacecraft's n-struments. f you decide YES, what will you do to com-municate with Earth through Viking? Design a messageto Earthmen from your civilization, remembering thatEarthmen cannot read your language and may not evenunderstand your symbology. For example, an arrow-head on Earth is a symbol of directions and was devel-oped as a result of man's early use of bows and arrows,something unknown on Mars.If you decide NO, how will you try to fool Viking?

and use t with hydrogen from water to produce organicmolecules. Oxygen from the water is emitted by theliving systemas a waste product. It is believed that theEarth's atmosphere became oxygen-enriched by thisprocess.On Viking a quarter of one cubic centimeter ofMartian soil is placed into a container in which theMartian atmospherehas been changed to include car-bon monoxide and carbon dioxide made from radio-active carbon-14. For severaldays the sample s bathedin light simulating Martian sunlight. A living organismin the soil would be expected o assimilate carbon, someof which would be the radioactive isotope. Then theremaining gases n the chamber are flushed from thesample to remove all the remaining carbon-14, and thesample s immediately heated to 625C (1155F). Or-ganic materials are changed into gases that are passedinto a device that detects or the presenceof any carbon-14. Detection of this radioactive isotope will indicatethat something in the soil, most probably a living or-ganism, has extracted the carbon-14 from the atmos-phere. The second experiment places about twice asmuch Martian soil in a tube and moistens it with anutrient fluid labeled with carbon-14. The sample thenstands for about two weeks at a temperature of about10C (50F). If there are any microorganisms in thesample they would be expected o consume he nutrientand later releasegases ontaining the carbon as a wasteproduct. If a detector finds carbon-14 in the gas fromaround the sample he conclusion would be that a livingsystemexists on Mars able to absorb nutrients from afluid and exude carbon dioxide as a waste material.Many Earth life forms, including people, do just that.People eat food rich in carbon (see this carbon if youpvercook food in a skillet until it blackens), extractenergy by changing the complex molecules containingthe carbon into simpler molecules, and exhale carbondioxide as a waste product.The third biological experiment carried by theViking lander operates on "the basis that living creaturesmust alter their environment as they live, breathe, eat,and reproduce. Soil which has been moistened by waterrich in nutrients is incubated for close to two weeks ina sealed cup. Periodically the gas surrounding the soilsample s withdrawn and passed hrough an instrumentknown as a gas chromatograph. Thus any changes othe atmosphere surrounding the soil sample are de-tected; for example if methane and carbon dioxide havebe~n developed by a microorganism.But should all these nstruments fail to detect life,this will not mean that there is no life on Mars. Thelanders might have been set down in barren places. OrMartian life might not evenbe detected by these Vikinginstruments which are based upon what we know abouthow Earth life operates biologically.Besides looking for life, Viking will analyze thesurface materials of Mars. A soil sample will be bom-barded with X-rays which cause the soil atoms to flu-oresce by emitting other X-rays characteristic of thedifferent elements present in the sample. This experi-ment only tells what elements are present in the soil

Project TwoYou are a scientist at Viking Mission Control in Cali-fornia and on one of the pictures returned from thelander you ~e a group of curious cr.eaturesstandingstill and examining the lander. They were not on theprevious picture and have vanished on the next picture.You see hem in color and in stereo or 3D. You have to


12/12

SUGGESTED READINGnform the U.S. President about this amazing discovery.Write your report describing what you see in the pic-ture, what you think it implies; recommend what shouldbe done and point out the possible dangers or benefitsto humanity from discovering this life form on Mars.Viking, Mission to Mars

W. R. Corliss, NASA SP-334, 1974, U.S. Govt.Printing Office Stock Number 3300-0561Progress Report on Project Viking

R. N. Watts, Jr., Sky and Telescope, .44, n.5November 1972, pp. 302-303The Search or Life on Mars

K. F. Weaver, National GeographicMagazine,v.143, n.2, February1973,pp. 264-265

Project ThreeExperimental detection of life by an optical techniqueUse the following equipment

Limewater,Ca(OH)2A test tubeA simple photoelectric lightmeterA soil sample with and without organicmaterial. Where the U.S. Will Land on MarsE. Driscoll, ScienceNews, v.103, n.17, 28 April1973, pp. 273-274

How We'll Search or Life on MarsG. Soffen, and J. S. Martin, Popular Science,February1971.

Method: Place the lime water in the test tube and takea reading of the light meter against the tube with afairly constant light source, a north-facing window forexample. Next insert a good amount of the soil sample.Watch how the presence of any organism that givesoff carbon dioxide will causea shift in the clarity of thewater Sind egister on the light meter.Suggest ow you might modify an experiment suchas his for use on Mars. Compare this experiment withthose in Viking that detect the production of carbondioxide by living organisms. List the advantages anddisadvantagesof the various methods.

The Viking Mission to Marsvarious authors, Icarus, v.16, n.1, February 1972,entire ssue.

For sale by the Superintendent of Documenta,U.S. Government Printing OfficeWashington, D.C...20402

Stock Number 033-000-00622-5

the viking mission

Documents