Viking Encounter Press Kit

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TABLE OF CONTENTS

GENERAL RELEASE ....................................... 1-9SCIENTIFIC GOALS OF THE VIKING MISSION ............... 10-13VIKING SCIENCE INVESTIGATIONS ........................14-61Orbiter Imaging ..................................... 14-18Water Vapor Mapping ................................ 18-22Thermal Mapping ....................................22-24Entry Science.........................................24-26Upper Atmosphere ...................................26-27Lower Atmosphere ....................................27-29Lander Imaging .....................................29-35Biology ............................................. 35Pyrolytic Release .................................. 35-38Labeled Release .................................... 38-39,P - Gas Exchange....................................... 9-41Molecular Analysis .......................... ...... 41-44Inorganic Chemistry ................................ 45-48Meteorology ........................................49-51Seismology .........................................52-54Physical Properties ................................54-56Magnetic Properties ................................56-59Radio Science ....................................... 59-61

VIKING SCIENTISTS .................................... 62-64VIKING PLANETARY OPERATIONS .......................... 65-93Approach Phase .....................................65-67Mars Orbit Insertion.............................. 7Pre-Landing Orbital Activities .....................67-68Landing Sites ......................................68-70Site Certification .................................70-73Pre-Separation Activities .......................... 3-74Separation .........................................74Entry Phase ........................................ 74-77Entry Science 7......................................7-79Touchdown .......................................... 79-81Landed Operations .................................. 1--83Sols 1 through 7 (July 5-12) ....................... 3-87Surface Sampling on Sol 8 (July 12) ................ 87-91Orbital Activities .................................91-93

VIKING LANDER ........................................94-102Lander Body .. 941LadrBoy................................. ..... ..... ....... ........ ..9Bioshield Cap and Bade .................... 94-96Aeroshell....................... .................Base Cover and Parachute System ...................6Lander Subsystems ..................................97

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iiXlDescent Engines .............................. 97Communication Equipment. ..........................7Landing Radars .................................. 98Guidance and Control ............................ 98Power Sources .................................... 99Data Storage .................................... 100-102

VIKING ORBITER.................................. 103-105Orbiter Design .................................. 103Structure. ................................... 103Guidance and Control ........................... 04Communications ..................................104-105Dat'a Storage .............................. 105LAUNCH AND CRUISE ACTIVITIES ........................ 06-109

Launch Phase......... ..........................106-107Cruise Phase....................................107-i09MISSION CONTROL AND COMPUTING CENTER ..............109-111Image Processing Laboratory .....................111TRACKING AND DATA SYSTEM ...........................112-113VIKING PROGRAM OFFICIALS .......................... 14-120CONVERSION TABLE ...................... ...........121

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) -Iwis NewsNational-Aeronautics andSpace AdministrationWashington, D C 20546AC 202 755-8370

Nicholas Panagakos For ReleaseHeadquarters, Washington, D.C. IMMEDIATE(Phone: 202/755-3680)

Maurice ParkerLangley Research Center, Hampton, Va.(Phone: 213/354-5011 - JPL)

RELEASE NO: 76-103

VIKINGS CONVERGE ON MARS

The Vikings are converging on Mars.

After almost a year-long chase through interplanetaryspace to overtake the planet, the first of two Viking space-craft is closing fast on Mars, aiming for orbit insertionon June 19.

If all goes well, the first Viking's Lander will touchdown on Mars on July 4, the 200th anniversary of the UnitedStates.

Seven weeks later Viking 2 will reach Mars. It willbegin orbiting the planet Aug. 7, and its Lander will touchdown about Sept. 4.

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The instrument-packed spacecraft, two Orbiters andtwo Landers, will photograph Mars from orbit and on thesurface, and conduct a detailed scientific examination ofthe planet, including a search for life.

Each Orbiter carries three investigations, each Landercontains eight more, and one investigation uses equipmentaboard both spacecraft.

The Orbiter's investigations will begin severa' daysbefore Viking 1 enters Mars orbit. Two high-resolutiontelevision cameras will take photograohs of the whole discof Mars, one of its moons and of star fields near the planet.At the same time, two infrared science instruments willbegin scanning the planet to map its surface temperat resand look for water vapor concentrations in its atmosphere.

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During the two weeks between orbit insertion andseparation of the Lander from the Orbiter, the Orbiter'sinstruments will carefully study the planned landing sites.

Selected several years ago, these sites will be furtherverified as safe places fo r the Lander. Huge radar antennason Earth wf1ll supplement data gathered by the Orbiter.Located at Goldstone, Calif., and Arecibo, Puerto Rico, theantennas will bounce radar echoes from the prime and backuplanding sites from May 11 to June 15. -I

Prime target fo r Lander 1 is in the Chryse "Land ofGold" region, at the northeast end of a huge canyon firstdiscovered by the Mats-orbiting spacecraft, Mariner 9. Thesite is 19.5 degrees north and 34 degrees west. Lander l'sbackup site is Tritonis Lacus, at 20.5 degrees north and252 degrees west.

Viking 2 's lander also has primary and backup sites.The primary site is Cvdonia, in the Mare Acidalium region,at the edge of the sou:!co-nos: reaches of the north polarhood. Cydonia is 44.3 degrees north and 1" degrees west.The backup site is called Alba, lying 44.2 degrees northand 110 degrees west.

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Another pair of sites has been selected by Vikingscientists in the event that Viking 2 primary and backupsites are deemed unsuitable for landinq.

No landing site is known to be completely free from hazards.'The task of the Viking site certification team is to compareall possible data and try to minimize hazards to the Landers.

Once the Viking 1 Landing site has been certified, theOrbiter and Lander will be ready for separation, scheduledfor about three hours before landing.

The Lander must survive the searing heat of entrythrough the planet's atmosphere, land gently on the surfaceand conduct an intricate series of scientific -.vesticvitions.

As the Lander enters the Martian atmosphere, se eralinstruments and sensors will measure the atmosphere's itruc-ture and chemical composition. A mass spectrometer, aretarding potential analyzer and several sensors will ieasureatmospheric composition, temperature, pressure and der ityin the upper atmosphere. Continued measurements will 'cmade in the lower atmosphere by other sensors on '-ho n

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One important aspect of the entry investigations islearning as much as possible about the presence of argonin the atmosphere. One Soviet Mars mission reported thepresence of as much as 30 per cent argon in the Mars atmospe-_e.Argon, an inert gas, could have considerable effect on someViking experiments, especially the gas chromatograph massspectrometer (GCMS).

Minutes after the Lander touches down on Mars, the takingof the first two surface photographs will begin. rhese will betelemetered to Earth through the Orbiter and should reachmonitors at the mission con trol center by about midnight(EDT) on the July 4 landing date.

Several other Lander science instruments will also beginoperation as soon as the craft touches down and, in the fol-lowing days, other instruments will study the planet's biology,molecular structure, inorganic chemistry and physical andmagnetic properties.

The Lander's surface sampler, attached to a furlableboom, will dig, up soil samples fo r incubation and analysisinside the biology instrument's three metabolism and growthexperiment chambers, in the GCMS instrument and in an X-rayfluorescence spectrometer (XRFS).

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These three investigations are particularly importantfor understanding the biological makeup of Mars, and theywill provide knowledge to other scientists on the chemistryand planetology of Mars.

The meteorology instrument, located on a folding boomattached to the Lander, will periodically measure tempera-ture, pressure, wind speed and direction during the mission.

A three-axis seismometer will measure any seismic acti-vity that takes place during the mission, which should estab-lish whether or not Mars is a very active planet.

The physical and magnetic properties of Mars will bestudied with several small instruments and pieces of equip-ment located on the Lander.

Radio science investigations will make use of Orbiterand Lander communications equipment to measure Mars' gravi-tational field, determine its axis of rotation, measuresurface properties, conduct certain relativity experimentsand pinpoint the locations of both Landers on Mars. Aspecial radio link, the X-band, will be used to study chargedion and electron particles.

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Viking mission controllers will use a new term tosignify time on Mars: Sol, which is the Viking Projectword for a Mars day. The special designation is necessaryto keep track of the difference between Earth and Mars days.Because of its rotation period, a Mars day is 24.6 Earthhours long (24 hours, 36 minutes).

The difference between Earth and Mars days also causesperiodic changes to the prime shiEt of mission controllers.In order to be on duty at about the same time each Mars day(Sol), controllers must move their work hcurs.

From an 8 a.m. to 4:30 p.m. schedule at the beginningof the planetary mission, controllers will shift, July 11,to a 4 p.m. to midnight shift. On July 24 the prime shiftchanges to midnight to 8 a.m., and Aug. 6 sees a return tothe regular day shift. This cycle will periodically repeat lthroughout the mission.

Another time problem is caused by the extremely longtransmission time required for telemetry of commands fromEarth an. data from Mars. One-way transmission, at thespeed of light, takes from 18 to 21 minutes awhile theVikings are operating on Mars.

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-8-Mission controllers who send a cownand to the Lander,for example, won't know whether the command was received

and executed for at least 36 minutes during the first daysof the planetary mission.

And confusion can occur if a particular event'time isn'tclearly designated. Viking l's landing, for example, isscheduled for 9:41 p.m. EDT, but mission controllers won'thave confirmation of landing until at least 9:59 p.m., whichis designated as Earth-Received Time (ERT).

Viking is under the overall management of the Officeof Space Science, NASA Headquarters, Washington, D.C. TheViking Project is managed by NASA's Langley Research Center,Hampton, Va. The Landers were built by Martin MariettaAerospace of Denver, Colo., which also has integrationresponsibility for Viking. The Orbiters were built byNASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

Nerve center of Viking operations is the Viking MissionControl and Computing Center (VMCCC), located at JPL. A7 50-perso:i flight team of engineers, scientists and techni-cians maintain constant control of the four Viking space-craft throughout the planetary phase of the mission.

(END OF GENERAL RELEASE. BACKGROUND INFORMIIATION FOLLOWIS.)

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THE SCIENTIFIC GOALS OF THE VIKING MISSION

Mars has excited man's imagination more than any othercelestial body except the Sun and the Moon. Its unusual red-dish color, which the ancients associated with fire and blood,gave rise to its being named for the Roman God of War.

The invention of the astronomical telescope by Galileoin 1608 opened a new era in the observation of the planet.Instead of appearing merely as a tiny disc, Mars' surfacefeatures could be resolved.Christian Huygens made the first sketch in 1659 of thedark region, Syrtis Major ("giant quicksands"). Able to

observe a distinguishable feature, Huygens could show thatMars rotated on a north-south axis like Earth, producing aday that was about half an hour longer than Earth's.

In 1666, the Italian astronomer Giovanni D. Cassiniobserved and sketched the Martian polar caps. Observersin the early 1700's noted changes in the surface appearancein a matter of hours, probably caused by dust storms, nowknown to rage periodically. In 1783, William Herschel ob-served that Mars' axis of rotation is inclined to its or-bital plane at about the same extent as Earth's, revealingthat long-term changes were often associated with seasonsthat would result from such inclination.

In the 17th and 18th centuries, it was commonlyaccepted that Mars and the other planets were inhabited,but the real excitement was created by Giovanni Schiaparelliand Percival Lowell between 1877 and 1920. As a result ofextensive observations, beginning with the favorable appari-tion of 1877, Schiaparelli constructed detailed maps withmany features, including a number of dark, almost straightlines, some of them hundreds of kilometers long. lie referredto them as "canali" or channels. Through mistranslation, theybecame "canals" and the idea of civilized societies was propa-gated.

Lowell's firm opinion that the canals were not naturalfeatures but the work of "intelligent creatures, alike tous in spirit but not in form" contributed to the colorfulliterature. To pursue his interest in the canals and ;,ars,he founded the Lowell Observatory near Flagstaff, Ariz., in1894 and his writings about the canals and possible life onMars created great public excitement near the turn of the20th Century.

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-11- , Speculation about intelligent life on Mars continuedthrough the first part of the century, with no possibilityof an unequivocal resolution, but a gradual tendency devel-oped among scientists to be very skeptical of the likelihood.The skepticism was reinforced by the results of Marinerflyby missions, one in 1965 and two in 1969. The limitedcoverage of only about 10 per cent of the Martian surface byflyby photography indicated that Mars was a lunar-like planetwith a uniformly cratered surface.In 1971-72 the Mariner 9 orbiter revealed a completelynew and different face of Mars. Whereas the flyby coveragehad seen only a single geologic regime in the cratered high-lands of the southern hemisphere, Mariner 9 revealed gigantic

volcanoes, a.valley that extends a fifth of the way aroundthe planet's circumference, and possible evidence of flowingliquid water sometime in the past. Also revealed were layeredterrain in the polar regions and the effects of dust moved bywinds of several hundred kilometers an hour.In short, Mariner 9's 7,000 detailed pictures revealeda dynamic, evolving Mars completely different from the lunar-like planet suggested by the flyby evidence. That successfulOrbiter mission showed a fascinating subject for scientificstudy and also provided the maps from which the Viking siteshave been selected.The scientific goal of the Viking missions is to "increaseour knowledge of the planet Mars with special emphasis on thesearch for evidence of extra-terrestrial life." The scientificquestions deal with the atmosphere, the surface, the planetarybody and the question of bio-organic evolution. This goalultimately means understanding the history of the planet.The physical and chemical composition of the atmosphereand its dynamics are of considerable interest, not only becausethey will extend our understanding of planetary atmosphericsciences, but because of the intense focus of interest in con-temporary terrestrial atmospheric problems.Scientists want to understand how to model our own atmos-

phere more accurately and they want to know how the solar windinteracts with the upper atmosphere; to do this more must beknown about atmospheric chemistry, the composition of neutralgases and charged particles.Researchers want to reconstruct the physics of the atmos-phere and determine its density profile. They want to measurethe atmosphere down to the surface and follow its changes, dailyand seasonally. From these data may come clues to the atmos-pheric processes that have been taking place and determiningthe planet's character.

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Of special interest is the question-of water on Mars.Scientific literature is sparse in data and rich in specu-lation. It is known that there is water in the Mars atmos-phere, but the total pressure of the atmosphere (about 1per cent of Earth's) will not sustain any large bodies ofliquid water. Nevertheless, the presence of braided chan-nels suggests to many geologists that they are the resultof previous periods of flowing water. This idea of episodicwater suggests a very dynamic planet.

The geology of Mars has attracted great interest amongplanetologists because of the wide variety of features seenin the Mariner photos.

Volcanologists are intrigued by the high concentrationof volcanoes near the Tharsis ridge. Scientists who studyerosion are fascinated with the great valley (VallesMarineris) that is 100 kilometers (62 miles) wide,3,nnO km(1,800 mi.) long and 6 km (4 mi.) deep. Some geologistshave focused on the polar region, which appears to be stra-tified terrain. The pole resembles a rosette; it has beensuggested that this is evidence of precession (wobbling) ofthe poles. One important question that Viking is not likelyto answer, due to payload limitation, is the age of theplanet.

One mystery that Viking may solve is the fate of nitro-gen. So far there has been no report of nitrogen on Mars.Has it been lost by outgassing? Is it locked up in the sur-face as nitrates or in some organic form? Chemists and bio-logists both look upon nitrogen, among the most cosmicallyabundant of the elements, as vitally important because ofthe clues it provides to the evolution of the atmosphere andof the planet itself.There is the final question of life on Mars. This may

be one of the most important scientific questions of ourtime. It is also one of the most difficult to answer.A negative answer does not prove there is no life on

Mars. The landing site may have been in the wrong place,during the wrong season, or we may have conducted the wrongexperiments. Many scientists still think there is a lowprobability of life on Mars.

flow can this extensive effort to perform the searchbe justified? First, it must be aknowledged that there isno evidence at present, pro or con, of the existence of lifeon Mars. And what experimcnters seek is evidenco,

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Dr. N. H. Horowitz, Professor of Biology, CaliforniaInstitute of Technology, stated: "The discovery of life onanother planet would be one of the momentous events of humanhistory."

Finally, a knowledge of the organic character of th eplanet is regarded as of utmost importance. Whether lifehas begun or not, it is critical to our concept of chemicalevolution to determine the path of carbon chemistry. Marsoffers the first opportunity to gain another perspective inthe cosmic history of planetary chemistry.

The scientific investigations of Viking were inten-tionally selected to complement one another. The Orbiterscience instruments are used to help select landing sitesfor the Lander investigations. The Lander cameras helpselect soil samples for the chemical and biological analyses.The meteorology data are used to determine periods of quietfor the seismology experiment. The atmospheric data are usedin determining the chemistry, which in turn is used in under-standing the biological result.

But Viking's greatest asset is its flexibility. Thescientist-engineer teams will be interacting, hour by hour,during the months that Viking will be returning data. Everyday will bring new discoveries and fresh ideas for improvingthe mission to extract the maximum benefit from this effort.

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-14-VIKING SCIENCE INVESTIGATIONz

Three science investigations use instruments locatedon the Orbiter: orbiter imaging, atmospheric water vapormapping and thermal mapping. One investigation, Entry Science,located on the Lander, is conducted while the Lander is des-cending to the surface of Mars.Eight other investigations are conducted from theLander: lander imaging, biology, molecular analysis, in-organic chemical analysis, meteorology, seismology,physical properties and magnetic properties. One investiga-tion, radio science, has no specific instrument, but usesthe Viking telecommunications system to obtain data and docertain experiments.

Orbiter ImagingThe orbiter imaging investigation has four objectives:* Add to the geologic knowledge of Mars by providinghigh-resolution photographic coverage of scientificallyinteresting areas of the Martian surface.* Add to the knowledge of dynamic processes on Marsby observing the planet during seasons never before seen.* Provide high-resolution imaging data of the Vikinglanding sites before landing so site safety and scientificdesirability can be assessed.* Monitor the region around each landing site afterlanding so the dynamic environment in which Lander experi-ments are done is better understood.The Visual Imaging Subsystem (VIS) consists of twoidentical cameras, mounted side by side on the Orbiter'sscan platform.The cameras will be used in different ways as the mis-sion progresses. As Viking 1 approaches Mars, the planetwill be photographed in three colors. The planet's atmos-phere is expected to be clear, in contrast to the 1971Mariner 9's approach to Mars, allowing the first usefulapproach pictures since 1969.

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Between Mars orbit insertion and landing the cameraswill be used almost exclusively for examining the landingsite. The intent is to characterize in detail terrain at thesite and make estimates of slopes at the Lander scale; examinethe region of the site for both long and short-term changesthat might indicate wind action; and monitor any atmosphericactivity.

For most of the period after landing, the Orbiter willbe a communications relay link for the Lander and its orbitwill remain synchronized with the Lander; i.e., it willpass over the Lander at the same time each day. Areas visi-ble from the synchronous orbit will be systematically photo-graphed during this time. Areas covered will include thelarge channel system upstream from the primary landing site,chaotic terrain from which many of the channels seem to ori-ginate, and areas of greatest canyon development.The detailed observations are expected to lead to abetter understanding of the origin of these features, andaid in interpreting Lander data. At the same time, activi-ty will be monitored over all the planet that is visiblefrom apoapsis. Any areas of unusual activity will also beexamined in detail. The orbital period will be changed forshort periods of time to allow the rest of the planet to beseen. During these periods, observations will be made oflarge volcanoes, channels and other features.Viking 2 will follow a simnilar plan, except for onemajor difference: shortly after Lander 2 lands, the orbitalinclination of Orbiter 2 will be increased to perform polarobservations. After the inclination change, a period ofsystematic mapping of the north polar region is anticipated,similar to that undertaken in the canyon lands by Orbiter 1.The succession of deposits in the polar regions, theirthicknesses and relative ages, will be determined with theseobservations. This portion of the mission is particularlyimportant because of its potential for unraveling F-st cli-matic changes and assessing the volatile inventory (primarilycarbon dioxide and water) of the planet.Each visual imaging subsystem consists of a telescope,a camera head and supporting electronics. The telescopefocuses an image of' the scene being viewed on the faceplateof a vidicon within the camera head. WThen a shutter betweentelescope and vidicon is activated, an imprint of the sceneUs left on th e vidicon faceplate as a variable electrostaticcharg;e. The faceplate is then scanned with an electronicbeam and variations in charge are read in parallel onto aseven-t-rack tape recorder.

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Data are later relayed to Earth one track at a time.A picture is assembled on Earth as an array of pixels

(pic-ture elements), each pixel representing the charge at a pointon the faceplate (i.e., the brightness at a point in the image).As data are read back, the pixel array is slowly assembled,complete only when all seven tracks have been read. The imageis then displayed on a video screen and film copies are made.

The telescope has an all-spherical, catadioptric casse-grain lens with a 475-millimeter (18.7-inch) focal length.The sensor is a 38 mm (1.5-in.) selenium vidicon. A mechani-cal focal plane tape allows exposure times from 0.003 to 2.7seconds. Between the vidicon and telescope is a filter wheelthat provides color images. Each frame has 8.7 million bits(binary digits).

The cameras are mounted on the Orbiter with a slightoffset and the timing of each shutter is offset by one-half-frame time so the cameras view slightly different fields andshutter alternately. The combined effecc is to produce aswath of adjacent pictures as the motion of the spacecraftmoves the fields of view across the surface of Mars. Theresolution at.the lowest part in the orbit (1,500 km or810 mi.) is 37.5 m (124 ft.) per pixel. This wouldallow an object the size of a football field to be resolved.

The Orbiter Imaging investigationteam leader is

Dr. Michael 1I. arr of the U.S. Geological Survey, MenloPark, Calif.

Water Vapor MappingWater vapor is a minor constituent of the Martian

atmosphere. It:; presence was discovered about / years agofrom Earth-based telescopic observations. They/ indicatedthat the vapor varies seasonally, appearing and disappearingwith the recession and growth of the polar c in each hemi-sphere, and diurnally (daily), with its maxmum close tolocal (Mars) noon (Mars time). Some e.vid ce was found Ithatwater vapor is contained in the lowest layers of the atmosphere,perhaps within the first 1,000 m (3,30 ft.) above the surface.

The abundance of atmospheric ater vapor is usuallygiven in units of "precipitable yipcrons," a measure of thethickness of the ice layer or liquid that would be formedif all the vapor in the atmospheric column above the surfacewere condensed out.

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Compared with Earth, Mars' atmosphere contains verylittle water. The atmosphere on Earth typically holdsthe equivalent of one or two centimeters (0.4 to 0.8 inches)of water, but the most water observed on Mars is only a frac-tion of one per cent of Earth's or 50 precipitable microns(0.002 inches).The Mars atmosphere is a hundred times thinner thanEarth's, however, and its mean or average temperature isconsiderably lower. The relative water concentrations, there-fore, are not very different (about one part per thousand)and the relative humidity on Mars can be significant attimes. It is misleading to refer to Mars as a "dry" planet.

Yet in terms of total planetary abundance, evidence sug-gests that there is very little water on or above the planet'ssurface in the form of atmospheric vapor or surface ice.Since water is cosmically one of the more abundant molecules,the question arises: Has Mars lost most of its water duringits evolution, or is water present beneath the surface, asubsurface shell of ice or permafrost, or perhaps held deeperin the interior to be released by thermal and seismic acti-vity at some future time?

Mariner spacecraft observations of Mars in 1969 and1971 showed that while the polar hoods are predominantlyfrozen carbon dioxide, the visible caps left after the car-bon dioxide vaporizes are water crystals.Mariner results revealed other intriguing facts relatedto the history of water on Mars: The atmosphere loses hydro-gen and oxygen atoms to space at a slow but steady rate, andin the relative proportions with which they make up the watermolecule. Surface features exist that appear to have beenformed by flowing liquid . Thelatter are quite differentfrom the river-like features caused by lava flows. Theyappear to be wide braided channels formed from an earlierperiod of flooding by a more mobile liquid than volcanic lava.Again a question: Are we now seeing the last disappear-ing remnants of water that was once much more plentiful onthe planet, or is Mars locked in an ice age that has frozenout most of its water in the polar caps or beneath a layerof surface dust?Martian water clearly holds many clues to the planet'shistory. By studying the daily and seasonal appearance anddisappearance of water vapor in more detail than is possiblefrom Earth by mapping its global distribution, and by deter-mining the locations and mechanisms of its release ibto theatmosphere, scientists should understand more clearly thepresent water regime, and perhaps unravel some of the mysterysurrounding past conditions on the planet.

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In the context of Martian biology, such clarificationmay have great significance in establishing the existence,now or in the past, of an environment favorable to the sur-vival and proliferation of living organisms. This presumesthat Martian life is dependent on the availability of wateras is life on Earth.The Viking water vapor mapping observations will bemade with an infrared grating spectrometer mounted on theOrbiter scan platform, boresighted with the television camerasand the Infrared Thermal Mapper (IRTM). The spectrometer,called the Mars Atmospheric Water Detector (MAWD), measuressolar infrared radiation reflected from the surface of theplanet after it has passed through the atmosphere.The instrument selects narrow spectral intervalscoincident with characteristic water vapor absorptionsin the 1.4-micron wavelength region of the spectrum. Varia-tions in the intensity of radiation received by the detectorsprovide a direct measure of the amount of water vapor in theatmospheric path traversed by the solar rays.The sensitivity of the instrument enables amountsof water from a minimum of a precipitable micron to a maxi-mum of 1,000 microns to be measured. The precise wavelengthsof radiation to which the detectors respond are also selectedso instrument data can be used to derive atmospheric pressure

at the level where the bulk of the water vapor resides, pro-viding an indication of its height above the surface.At the lowest point in the orbit, the field of view ofthe detector is a rectangle 3 by 20 km (1.9 by 12.4 mi.) onthe planet's surface. This field is swept back and forth,perpendicular to the ground track of the Orbiter, by anauxiliary mirror at the entrance aperture of the instrument.In this way the water vapor over selected areas of the planetcan be mapped.A small ground-based computer, dedicated to the useof the two orbiting infrared isntruments, directly reducedata to contour plots of the water vapor abundance and pres-

sure.During the initial orbits, and particularly through thelanding site certification phase of the missions before Landerseparation, MAWD observations will concentrate on an area withina few hundred kilometers around the landing sites, to help insite certification and to complement landed science measurements.

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In later phases of the mission, observations will beextended to obtain global coverage of water vapor distribu-tion and its variation with time-of-day and seasonal progres-sion. The search for regions of unusually high water contentwill be emphasized during these later stages, and areas ofspecial interest will be studied, including volcanic ridges,the edge of the polar cap and selected topographic features.

The Water Vapor Mapping investigation team leader isDr. Crofton B. (Barney) Farmer of the Jet Propulsion Labora-tory.Thermal Mapping

The Thermal Mapping investigation is designed to obtaintemperature measurements of areas on the surface of Mars.It obtains the temperature radiometrically with an InfraredThermal Mapper (IRTM) instrument.

Information obtained by the thermal mapper will contri-bute to the study of the surface and atmosphere of Mars, whichis similar to and in some ways simpler to study than Earth.Mars appears to be geologically younger, and clearly is under-going major changes. Studies of Martian geology and meteo-rology can have implications in tectonics (the study ofcrustal forces), volcanology and understanding weatheringand mineral deposition.Just as fine beach sand cools rapidly in the eveningwhile large rocks remain warm, daily temperature variationof the Martian surface indicates the size of individualsurface particles, although the thermal mapper necessarilyobtains an average value over many square kilometers. Measure-ments obtained just before sunrise are especially valuable(the detectors can sense the weak heat radiation from thedark part of the planet), since at that time the greatesttemperature differences occur between solid and fine-grained Xmaterial.One detector is used to measure the upper atmospherictemperature. That information may be combined with surfacetemperatures to permit construction of meteorological models.

An understanding of the important Martian wind circulationdepends on such models.Data received from the thermal mapper are intendedto help establish and evaluate the site for the VikingLander. Martian organisms would probably be affected bylocal water distribution and temperatures of the soil andair; these factors are either measured by the radiometeror are dependent on the soil particle characteristics deter-mined by the thermal mapper.

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The Infrared Thermal Mapper is a multi-channel radiometermounted sn the Orbiter's scan platform. It accurately measuresthe temperatures of the Martian surface and upper atmosphere,and also the amount of sunlight reflected by the planet. Foursmall telescopes, each with seven sensitive infrared detectors,are aimed parallel to the Visual Imaging optical axis. Dif-ferences of one degree Celsius (about 1.8 degrees Fahrenheit)can be measured throughout the expected temperature range ofminus 130 degrees C to plus 57 deagrees C (ittinus 202 to 135degrees F.). The instrument is 20 by 30 cii (8x10x12 in.) andhas a minimum spatial resolution of 8 km (5 mi.) on the surface.

The large number of detectors (28) is chosen to providegood coverage of the Martian surface, and to allow severalinfrared "colors" to be sampled. Differences in the apparentbrightness of a spot on the planet in the various colors implywhat kinds of rocks (granite, basalt, etc.) are present. Thetemperatures themselves may indicate the composition ofclouds and the presence of dust in the atmosphere.The spatial resolution available to the thermal mapperwill permit reliable determination of the frost compositioncomprising the polar caps. The close spacing of infrareddetectors and the spacecraft scanning mode improves theability to identify possible local effects such as currentvolcanic activity or water condensation.The Thermal Mapping investigation team leader is

Dr. Hugh H. Kieffer of the University of California atLos Angeles.

Entry ScienceThe Entry Science investigation is concerned withdirect measurements of the Martian atmosphere from the timethe Lander and Orbiter separate until the Lander touches downon the planet's surface. Knowledge of a planet's atmosphere,both neutral and ionized components tells much about theplanet's physical and chemical evolution, and it increasesunderstanding of the history of all planets, including thatof Earth.

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The question of the atmospheric composition of Marsis of immediate interest to scientists. Nitrogen, believedessential to the existence of life, has not yet been measuredon Mars by remote sensing methods. Measurements of atmos-pheric pressure and temperature, plus winds, are importantin understanding the meteorology, just as observations madewith weather balloons in Earth's atmosphere supplement sur-face observations.Upper Atmosphere. Studies of the Martian upper atmospherecomposition begin shortly after the Lander leaves the Orbiter.The first measurements are made so high above the surfacethat only charged particles can be detected. These measure-ments are made with a Retarding Potential Analyzer (RPA) thatwill measure electron and ion concentrations and temperaturesof these components. Measurements continue down to about 100km (60 mi.) above the planet's surface, where the pressurebecomes too high for the instrument to operate.

On Mars, which has a weak magnetic field compared withthat of Earth, charged particles streaming from the Sun(called the solar wind) and interacting with the upperatmosphere may be important in determining the nature ofthe lower atmosphere.At the very highest altitudes, the analyzer will studythe interaction of the solar wind with the Martian atmosphere.

Measurements at lower altitudes will make important contribu-tions to knowledge of the interaction of sunlight with at-mospheric gases, a matter of great significance in under-stand-ing the photochemical reactions that take place in allplanetary atmospheres, including Earth's.Another analyzer will be turned on several thousandkilometers above the Martian surface, but the neutral atmos-phere at high altitudes is so thin that measurements willnot begin until the Lander drops to an altitude of around300 km (180 mi.) above the surface. Measurements on the neu-traL constituents of the atmosphere are made with the UpperAtmosphere Mass Spectrometer (UAMS).The mass spectrometer will sample and analyze theatmosphere as the Lander passes through. Inside the instru-ment, the gas to be analyzed is ionized by an electron beam,and the ions formed are sent through an appropriate combina-tion of electric and magnetic fields to determine the amountsof the various molecular weights by which the various gasescan be identified.

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2 -The atmosphere of Mars appears to be windy compared toEarth's lower atmosphere. This is a result of the low densityof the atmosphere, which permits it to change temperaturerapidly, and causes large temperature variations from day tonight and seasonally. There are large contrasts in tempera-ture of the atmosphere, precisely the condition to create winds.One evidence fo r high winds is th e frequently severe duststorms, such as the long-lasting one that greeted Mariner 9.These storms are a puzzle, since it takes even strc:.ger windsthan those now calculated by computer models of the atmosphericcirculation (18 to 46 m per second; 40 to 100 mi. per hour)toraise dust in this tenuous atmosphere.The vertical profiles of temperature will provideadditional evidence of the thermal balance of the atmosphere

and, it is hoped, of forces that drive the winds. Winds alsowill be measured directly in the parachute phase by trackingthe motion of the Lander over the surface as it drifts, carriedby local winds. These measurements will extend to an altitudeof 6 km (3.7 mi.).The Entry Science investigation team leader is Dr. Alfred0. C. Nier of the University of Minnesota.

Lander ImagingAs a person depends on sight fo r learning about th eworld, so cameras will serve as th e eyes of the Lander and,indirectly, of the Viking scientists.Pictures of th e region near the Lander will be studiedto select a suitable site for acquiring samples that will beanalyzed by other Lander instruments. The cameras will alsorecord that the samples have been correctly picked up anddelivered. From tire to time, the cameras will examine dif-erent parts of the Lander to see that components are operatingcorrectly.One category of the Lander imaging investigation is th estudy of general geology or topography. Pictures of the Mar-tian surface visible to the cameras are of the highest scien-

tific priority. The first pictures will be panoramic surveys,and then regions of particular interest will be imaged inhigh resolution, in color and in infrared.

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K-32-Stereoscopic views are obtained by photographing thesame object with two cameras, providing photos in which three-

dimensional shapes can be distinctly resolved. Putting to-gether this information, scientists can tell much about thecharacter of the Martian surface and the processes that haveshaped it.

One can imagine finding shock-lithified rocks (as on theMoon), igneous.boulders, wind-shaped boulders (ventifacts),sand ripples, or a lag gravel deposit. Each of these pos-sible objects could be resolved in pictures; each would bespeaka particular kind of surface modification.The advantage of operational flexibility is important.

Scientists will study the first pictures and, on the basisof what they reveal, select particular areas for more de-tailed examination. This method will require sending newpicture commands to the Lander every few days.

Used as photometers, the cameras will yield data thatpermit inferences about the chemical and physical proper-ties of Martian surface materials. Color and IR diodes willcollect data .i.n six different spectral bands. Reflectancecurves constructed from these six points have diagnosticshapes for particular minerals and rocks. For example, dif-fering degrees of iron oxidation cause varying absorption inthe range from 0.9 to 1.1 micron wavelengths.

Another goal will be to spot variable features. Changesin features can be determined by taking pictures of the sameregion at successive times. The most probable change will becaused by the movement of sand and silt by the wind. Marinerpictures have revealed large-scale sediment movement; similarLander observations are anticipated.

A grid target has been painted atop the Lander; oneaim of the variable features investigation is to spe ifthe target is being covered by sediment. The came.os single-line scan will be used each day to detect any sand grainssaltating (hopping) along the surface.The most spectacular variable feature would be one of

biological origin. Many scientists are skeptical about theprobability of life on Mars; very few expect to see largeforms that can be recognized in a picture. The possibilitywill not be discounted, however. If there are organic forms,they might be difficult to identify in a conventional "snap-shot," Their most recognizable attribute might be motion, andthis motion might be uniquely characterized by the single-line-scan mode of operation.

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Another area of camera investigation is atmosphericproperties. Pictures taken close the horizon at sunset orsunrise will be used to determine the aerosol content ofthe atmosphere. Some pictures will also be taken of celes-tial objects: Venus, perhaps Jupiter, and the two Marssatellites, Phobos and Deimos. The brightness of theseobjects will be affected by the interference of the atmos-phere, and che cameras can provide a way to measure aerosolcontent.

The cameras can also be used in the same way as moreconventional surveying instruments. Pictures of the Sun andplanets can be geometrically analyzed to determine the lati-tudinal and longitudinal position of the Lander on Maris.

Each Lander is equipped with two identical cameras,positione' about 1 m (39 in.) apart. They have a rela-tively unobstructed view across the area that is accessibleto the sirface sampler. The cameras are on stubby maststhat extend 1.3 m (51 in.) above the surface.

The imaging instruments are facsimile cameras.Their design is fundamentally different from that of thetelevision cameras that have been used on most unmannedorbital and flyby spacecraft. Facsimile cameras use mechani-cal instead of electronic scanning.In a television camera the entire object is simul-taneously recorded as an image on the face of a vidicontube in the focal plane. Then the image is "read" by thevidicon through the action of an electron beam as it neu-tralizes the electro static potential produced by photonswhen the image was recorded. In a facsimile camera, smallpicture elements (called pixels) that make up the totalimage are sequentially recorded.In a facsimile camera an image is produced by observingthe object through sequential line scans with a nodding mir-ror which reflects the light from a small element of theobject into a diode sensor. Each time the mirror nods, onevertical line in the field of view is scanned by the diode.

The entire camera then moves horizontally by a small in-terval and the next vertical line is scanned by the noddingmirror. Data that make up the entire picture are slowlyacc.umulrted in this way.

Because each element (spot) in the field of view isrecorded on the same diode, opposed to different parts ofthe vidicon tube face the facsimile camera has a photo-metric stability that exceeds most television systems.Pelatively subtle reflectance chatacteristics of objectsin the field of view can be measured.

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There are actually 12 diodes in the camera focalplane; each diode is designed to acquire data of parti-cular spectral and spatial quality. One diode acquires asurvey black-and-white picture. Three diodes have filtersthat transmit light in blue, green and red; together thesediodes record a color picture. Three more diodes are usedin essentially the same way, but have filters that transmitenergy in three bands of near-infrared.Four diodes are placed at different focal positionsto get the best possible focus for high-resolution black-and-white pictures. (This results in a spatial resolutionof several millimeters for the field of view closest to thecamera--objects the size of an aspirin can be resolved.)The twelfth diode is designed with low sensitivity so itcan image the Sun.The survey and color pictures have a fixed elevationdimension of 60 degrees; high-resolution pictures have afixed dimension of 20 degrees. The pictures can be posi-tioned anywhere in a total elevation range of 60 degreesbelow to 40 degrees above the nominal horizon. The azimuthof the scene is adjustable; it can vary from less than onedegree to almost 360 degrees to obtain a panorama.The facsimile camera acquires data relatively slowly,line by line. Rapidly moving objects, therefore, will not

be accurately recorded. They might appear as a verticalstreak, recorded on only one or two lines. This apparentliability can be turned into an asset.If the camera continues to 'perate while its motionis inhibited, the same vertical line is repetitively scanned.If the scene is stationary, the reflectance values betweensuccessive lines will be identical, but if an object crossesthe region scanned by the single line, the reflectance valuesdramatically change between successive scans. The single-line-scan mode of camera operation, therefore, provides aniunusual way of detecting motion.As the mission proceeds, pictures will be acquired and

transmitted three ways: the first Lander pictures will besent directly to the Orbiter for relay to Earth. On succes-sive days, pictures will be acquired during the day andstored on the Lander's tape recorder for later transmissionto the Orbiter. Pictures can also be transmitted directlyto Earth at a lower data rate.

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The number of pictures that will be sent to Earth eachday will vary according to the size of the pictures, amountof data to be transmitted by other instruments, and lengthof the transmission period. A typical daily picture budgetfor one Lander might be one picture directly transmitted toEarth at low data rate, two pictures transmitted real timethrough the Orbiter, and three pictures stored on the taperecorder and later relayed to Earth.

The Lander Imaging investigation team leader isDr. Thomas A. (Tim) Mutch of Brown University.

BiologyBiology investigations will be performed to search for

the presence of Martian organisms by looking for productsof their metabolism. Three distinct investigations willincubate samples of the Martian surface under a number ofdifferent environmental conditions. Each is based on adifferent fundamental assumption about the possible require-ments of Martian organisms; together they constitute a broadrange of ideas on how to search for life on Mars. The threeinvestigations are Pyrolytic Release (PR), Labeled Release(LR) and Gas Exchange (GEX).

Martian soil samples acquired by the surface sampler,several imes during each landing, will be delivered to theViking Biology Instrument (VBI). There the samples will beautomatically distributed, in measured amounts, to the threeexperiments for incubation and further processing.

Within the biology instrument, a complex system ofheaters and thermo-electric coolers will maintain the in-cubation temperatures 'Between about 8 and 17 deqrees C(46 to 63 degrees F.) in spite of external temperatures thatmay drop to minus 75 degrees C (minus 103 degrees F.) orinternal Lander temperatures that may rise to 35 degrees C(95 degrees F.).

Pyrolytic Release. The Pyrolytic Release (PR) experimentcontains three incubation chambers, each of which can beused for one analysis. Tunis experiment is designed to measureeither photosynthetic or chemical fixation of carbon dioxide(CO2) or carbon monoxide (CO). The main rationale for this isthat the Martian atmosphere is known to contain C02 , with COas a trace component. Any Martian biota (animal or plant life)are expected to include organisms capable of assimilating oneor both of these gases. It also seems reasonable that at leastsome organisms on Mars would take advantage of solar energy,as occurs on Earth, and that Martian soil would include photo-synthetic organisms.

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The experiment incubates soil in a Martian atmosphere withradioactive CO and CO2 added. Then, by pyrolysis (heating athigh temperatures to "crack" organic compounds) and the useof an organic vapor trap (OVT), it determines whether radio-active carbon has been fixed into organic compounds. Thisexperiment can be conducted either in the dark or light.

For an analysis, 0.25 cc of soil is delivered to atest cell, which is then moved to 'he incubation stationand sealed. After establishing the.. incubation temperature,water vapor can be introduced by ground command if desired.Then the labeled C02 /CO mixture is added from a gas reservoirand a xenon arc Lpaxp, simulating the Sun's energy, is auto-matically turned on during the five-day incubation.

After incubation, the teLt cell is heated to 120 degreesC (248 degrees F.) to remove residual incubation gases, whichare vented to the outside. Background counts are made, afterwhich the test cell is moved from the incubation station toanother station.

Here pyr-lysis is done by heating the test cell to 625degrees r (1,160 degrees F.), while purging the test cellwith helium gas. The purged gases pass through the OVT, de-signed to retain organic compounds and fragments, but not C02or CO. The radioactivity detector at this stage will sense a"first peak" consisting mainly of unreacted C02/CO. This firstpeak is regarded as non-biological in origin.After this operation, the test cell is moved away fromthe pyrolysis station, the detector is heated and purged withhelium, and background counts are taken once more to verifythat the background radiation is down to pre-pyrolysis levels.The trapped organic compounds are then released from the OVTby heating it to 700 degree- C (1,290 degrees F.), which

simultaneously oxidizes thera to CO2 . These are flushed intothe detector. A significant second radioactive peak at thispoint would indicate biological activity in the original sample.

Labeled Release. The Labeled Release (LR) experiment is de-signed to test metabolic activity in a soil sample moistenedwith a dilute aqueous solution of very simple organic com-pounds. The rationale for this experiment is that someMartian organisms, in contact with an atmosphere containingCOZ, should be able to break down organic compounds to CO;.The experiment depends on the biological release cf radio-active gases from a mixture of simple radioactive compoundssupplied during incubation.

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The test cell is provided 0.5 cc of soil sample and ismoved to the incubation station and sealed. The Martian at-mosphere is established in the test cell in this process.Before the radioactively-labeled nutrients (a mixture of for-mate, glycine, lactate, alanine, and glycolic acid; all com-pounds uniformly labeled with radioactive carbon) are added,a background count is taken. Then approximately 0.15 cc ofnutrients are added, and incubation proceeds for 11 days.

The atmosphere above the soil sample is continuouslymonitored by a separate radioactivity detector throughout theincubation, after which the test cell and detector are purgedwith helium. 'The accumulation of radioactive C02 (or otherradioactive gases) indicates the presence of life metabolizingthe nutrient. Data are collected for 12 days. These data willproduce a metabolic curve as a function of time. The shape ofthe curve can be used to determine if growth is taking place inthe test cell.Gas Exchange. The Gas Exchange (GEX) experiment measuresthe production or uptake of C02, nitrogen, methane, hydrogenand oxygen during the incubation of a Martian soil sample.The GEX experiment can be conducted in one of two modes:in the presence of water vapor, without added nutrients, orin the presence of a complex source of nutrients.

The first mode is based on the assumption that substrates(foodstuffs) may not be limiting il the Martian soil and thatbiological activity may be stimulated when only water vaporbecomes available. The second mode assumes that Martian soilcontains organisms metabolically similar to those found inmost terrestrial soils and that these will require organicnutrients for growth.

A single test cell is used for the experiment. Afterreceiving 1 cc of soil from the distribution assembly, thetest cell is moved to its incubation station and sealed.After a helium purge, a mixture of helium, krypton and C02is introduced into the incubation cell and this becomes theznitial incubation atmosphere. (Krypton is used as an inter-nal standard; helium is used to bring the test chamber pres-sure to approximately one-fifth of an Earth atmosphere.)

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At this point either 0.5 or 2.5 cc of a rich nutrient so-l-ution can be introduced. Using the lesser quantity, the soildoes not come into contact with the solution, and incubationProceeds in a "humid" mode. An additional two cc allows con-tact between the soil and the nutrient solution, which consistsof a concentrated aqueous mixture of nineteen aminoacids, vitamins, other organic compounds, and inorganicsalts. Incubation initially is planned to be in the humid modefor seven days, after which additional nutrient solution willadded. For gas analyses, samples (100 microiitrs of the atmos-phere above the incubating soil are removed through a gassampling tube. This occurs at the beginning of each incuba-tion and after 1, 2, 4, 8 and 12 days.

The sawple gas is placed in a stream of helium flowingthrough a coiled, 0.7 m (23 ft.) long, chromatograph columninto a thermal conductivity detector. The system used in theGEX experiment is very sensitive and will measure changes inconcentration down to about one nanomole (one-billionth of amolecule).

After a 12-day incubation cycle, a fresh soil samplecan be added to the test cell to begin a new incubation cycle;the medium can be drained and replaced by fresh nutrients; andthe originaL atmosphere is replaced with fresh incubationatmosphere. The latter procedure will be used if significantgas changes are noted in the initial incubation, on the assump-tion that if these changes are due to biological activity, theyshould be repeatable and should be enhanced. If of non-biolo-gical origin, they should not reappear.

Each incubation station also con-tains auxiliary heatersthat can be used to heat soil samples to approximately 160degrees C (320 degrees F.). The heaters will be activatedfor three hours in case one or more of the experiments indi-cates a positive biological signal, after which the experi-ment will then be repeated on the "sterilized" soil samples.This is the control for the experiment. The detection of lifewould only be acknowledged if there were a significant dif-ference between the "control" and the experiment.An electronic system within the Viking B3iolocgy Instru-

nt, containing tens of thousands of components, will auto-r ically sequence all events within the experiments, but willI- subject to commands from Earth. The electronic subsystem~il also obtain data from the experiments fo r transmission

;'arth.

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Identification of the relatively small and simple or-ganic molecules in the surface of Mars may enable comparisonof the present chemistry of the planet to chemistry we assumeexisted on Earth a few billion years ago. Conversely, com-pounds may be encountered that resemble the compositionof petroleum. From the distribution of individual structures,speculation can be made whether or not these hydrocarbons representchemical fossils remaining after the decomposition of livingsystems of earlier times (a theory favored for the originof petroleum on Earth).

While the major constituent of the Martian atmosphereis known to be carbon dioxide, there is a conspicuous ab-sence of terrestrially important gases like oxygen and nitro-gen, at least at the level of more than about one per cent.

Recent Soviet measurements indicate the possibilityof an appreciable amount of argon. The concentration wouldtell something of the early history of Mars. Informationabout minor constituents like carbon monoxide, oxygen, nitro-gent and possibly even traces of small hydrocarbons or ammoniais important to an understanding of the chemical and possiblybiological processes occurring at the surface of the planet.Periodic measurements during the day and during the entirelanded phase of the mission are required for this purpose.

Finally, because of the absence of nitrogen in theatmosphere, it is of interest to search for nitrogen-con-taining inorganic substances such as nitrates or nitritesin the surface minerals.

A Gas Chromatograph Mass Spectrometer (GCMS) waschosen for these experiments because of its high sensitivity,high structural specificity and broad applicability to awide range of compounds. Because mass spectra can be inter-preted even in the absence of reference spectra, detectionis possible of compounds not expected by terrestrial chemists.

'The spectrometer will be used directly for analysis ofthe atmosphere before and after removal of carbon dioxide,which facilitates the identification and quantification ofTminor constituents.

Identification of organic substances probably presentin surface material is a complex task because little isknown about their overall abundance (which may be zero,,,and because any one of thousands of organic substances, orany combination thereof, may be present.

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-44-Durinq the experiment, organic substances will be vapor-ized from the surface material by heating it to 200 degrees C(392 degrees F.), while carbon dioxide (labeled with 13 C, anon-racioactive carbon isotope) sweeps t'irough. The emergingmaterial is carried into a gas chromatographiz column (tenex),which is then swept by a carrier gas (hydrogen). While passingthrough this column (a thin tube filled with solid particles)substances entering the column are separated from each otherby their different degrees of retention on this solid material.After emerging from the column, excess carrier gas isremoved by passing the stream through a Dalladium separatorthat is permeable only to hydrogen; the residual streamthen moves into the mass spectrometer. This produces acomplete mass spectrum (from mass 12 to 200) every 10 secondsfor the entire 84 minutes of the gas chromatogram. The dataare then stored and sent to Earth.In this part of the experiment, materials that arevolatile at 200 degrees C (392 degrees F.) will be measured.The same sample is then heated to 5000 C (9320 F.) to obtainless volatile materials and to pyrolyze (crack by heating)those substances that are not volatile enough to evaporate.The results of the organic experiment will consist ofthree parts: interpretation of the mass spectra to identifycompounds evolved from the soil sample; reconstruction of themolecular structures of those substances that were pyrolyzedand gave only mass spectra of their pyrolysis products; andcorrelation of the compounds detected in the surface materialwith hypotheses of their generation on the Martian surface.The detection of inorganic gaseous materials such aswater, carbon dioxide or nitrogen oxides, produced upon heatingthe soil sample, may permit conclusions on the composition of;.inerals that comprise the inorganic surface material. Resultsof the inorganic experiment are expected to help in this corre-lation and vice versa.Atmospheric analyses are relatively simple and don'trequire much time, power or expendable supp.ies, but organicanalyses are more involved. They consume a considerable amountof power, produce a large amount of data that must be sent toEarth, and involve materials that are limited (labeled carbondioxide and hydrogen). For these reasons only three soilsampLes will be analyzed during each of the two missions.ConsLdering the limited source (the area accessible to thesurface sampler), this should be an adequate number of tests.The Molecular Analysis investigation team leader isDr. Klaus Biemann of the Massachusetts Institute of Technology.

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Inorganic ChemistryScientific questions, ranging from the origin of thesolar system to the metabolism of microbes, depend largelyon knowledge of the elemental chemical composition of sur-face material. The Inorganic Chemical investigation willgreatly expand present knowledge of the chemi-try of Mars,and it is likely to provide a few clues to help answer some ofthese questions.The conditions under which a planet condenses arethought to be reflected in its overall chemical composi-tion. The most generally recognized relationship is thatplanetary bodies forming closer to the Sun should be enrichedin refractory elements such as calcium, aluminum and zirconium,relative to more volatile elements such as potassium, sodium

anC rubidium.To be truly diagnostic, ratios of volatile/refractory

el6mental pairs must represent planet-wide abundances, whichwill certainly be distorted by local differentiative geochemi-cal processes (core/mantle formation, igneous and metamorphicdifferentiation, weathering and erosion, etc.). On the otherhand, gross variations should be apparent. More detailedinformation on local processes (from other experiments aswell as this one) will help reduce the effects of distortion.Weathering in a watery environment (especially onehighly charged with carbon dioxide, as is Mars' atmosphere)

leads to fairly distinctive residual products, whose natureshould be inferable from the inorganic chemistry data. Thisis especially so in concert with data from the Gas Chromato-graph-Mass Spectrometer (GCMS) (on the presence and perhapsthe identity of hydrate and carbonate minerals) and the Mag-netic Properties experiment (on oxidation states of iron).We hope, therefore, to obtain data of at least a corroborativesort bearing on the question of the possible former existenceof abundant liquid water on Mars.The experiment, reduced to essentials, consists ofexposing samples of Martian surface materials to x-rays fromradioisotope sources, which stimulate the atoms of the samplex to emit "fluorescent" x-rays. Each chemical element emitsx-rays at a very few, extremely well-defined energies. Thiseffect is analogous to the emission of visible light by cer-tain fluorescent minerals..when illuminated wi.t..th_"la~cY. JJAh." .By analyzing the energy of the fluorescent x-rays, the ele-ments in the sample and their relative abundances can beascertained.

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Because of characteristics inherent in thc technique,elements lighter (i.e., earlier in the Periodic Table) thanmagnesium are not individually measured. While several ofthese elements (e.g., nitrogen, carbon, oxygen) may beabundant and very important for biological processes, theirprecise abundance in surface materials is of relativelyminor interpretative value. Gross abundances should be de-ducible from x-ray data combined with data from other experi-ments, notably the GCMS and Magnetic Properties investigations.The sample delivered to the x-ray Fluorescence Spec-trometer (XRFS) by the surface sampler may be coarse-grainedmaterial up to 1.3 cm (0.5 in.) in diameter (the opening of ascreen in the funnel head) or fine-grained material that hasbeen passed by vibratory sieving through 2 mm (0.08 in.) cir-cular openings in the surface sampler head.The spectrometer contains a sample analysis chamberx-raysources, detectors, electronics, and a dump cavity. The unitweighs two kilograms (4.5 pounds). Facing each window ofthe -chamber are two sealed, gas-filled proportional counter(PC) detectors flanking a radioactive source.These sources (radioactive iron and cadmium) producex-rays of sufficient energy to excite fluorescent x-raysfrom the elements between magnesium and uranium in the Perio-dic Table. Elements before magnesium in the table can bedetermined only as a group, although useful estimates of theirindividual abundances may be indirectly achieved.The output of the detectors is a series of electricalpulses with voltages proportional to the energy of the x-rayphotons of the elements that produced them. A determinationof the energy level identifies the presence of that elermentand the intensity (count rate) of the signal is related toits concentration.A single-channel analyzer circuit divides the outputof each detector into 328 energy levels and steps througheach level, recording the accumulated count fo r a fixedperiod of time. A continuous plot of the count rate in eazhlevel produces a spectral signature of tho material.

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MeteorologyMeteorology science measurements on Mars will be ob-

ta'ined primarily from sensors mounted on a boom attached tothe Lander. Measurements will include wind speed, wind direc-tion and temperature. Atmospheric pressure will be measuredby- a sensor located inside the Lander and vented by a tube tothe outside. Readings will be obtained during approximately20 periods every Sol*(Mars day), each period consisting ofseveral instantaneous measurements.The Meteorology investigation is designed to increase

understanding of how the Martian atmosphere works. It willbe man's first opportunity to'directly

observe the meteorologyof another planet that obeys the same physical laws- as doesEarth's atmosphere. The opportunity to extend and refinecomprehension of how an atmosphere works, driven by the Sun'sradiation and subject to rotation.of the planet, should givebetter understanding of Earth's atmosphere.

Scientific goals of the experiment are to:* Obtain the first direct measurements of Martian

meteorology with instruments placedzin the atmosphere.'Until, now all information on wind speeds, for example,has come from theoretical calculations of the circulationof the atmosphere, or from calculations of the wind speedneeded to raise dust.

* Measure and define meteorological variations duringthe daily cycle (Sol). The validity of existing theories thatpredict these diurnal (daily) variations can be compared withmeasurements and the theories revised as needed.

* Measure some of the turbulent characteristics ofthe planetary boundary layer. The boundary layer is themain brake on atmospherid'circulation, and this circula-tion cannot be adequately understood until more is knownabout the turbulent dissipation of energy in the boundarylayer.

* Verify whether such well-known terrestrial phenomenaas weather fronts and dust devils occur on Mars by observingthe behavior of the atmosphere as these things pass near theLanders.

* Support other' ander science experiments by providinginformation needed for other experimtiits. Meteorology resultsduring the first few days, for example, should provide infor-mation on the best timeof d'ay- to -deploy- he sur-f ace-samplerboom to avoid damage from high winds.

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Modes include selection of various filters to determinefrequency content of seismic data, or to adjust for the bestpossible reception of specific types of data; a low samplingrate for readinc the general level of activity; a.high datarate for more detailed-examination of events; and a compressed,medium rate for continuous monitoring of Marsquakes. Thislaswt mode normally will be dormant, with the system operatingat lo. rate until activated by a quake event.

Since the amount of raw data produced by the seismo-meter is much g'reater than the capacity of telemetry, datamust be compressed to reduce quantity without seriously de-grading' uality. Normally, many 'samples are required forhigh-frequency data.Data compression is done in two ways. First', normalground noise (microseisms) is observed by averaging its

amplitude over a 15'1second period as it is passed throughselectable filters. Its average amplitude and frequencycontent can be indicated by one sample every 15 seconds.Second, when a Marsquake event occurs, a trigger acti-vates a. igher data rate mode that samples, not oscillationsin the data, but amplitude of'the overall event envelope.This varies at a much lower rate than individual oscilla-tions and requires only one amplitude sample per second toindicate its shape.At the same time, crossing of the zero axis by theoscillations (change in polarity of the data s.Xgnal) iscounted and sampled once per second. The shape of theenvelope and its incremental frequency content can be trans-.mitted' to Earth with relatively few data samples and recon-structed to approximate the original event.The Seismology investigation team leader is Dr. Don L.

Anderson of the California Institute of Technology.

Physical Properties

The Physical Properties investigation group frequentlyhas beer, called "the team without an instrument." While thestatement i's not quite true, the investigation mainly willuse available engineering data. Hardware for the investiga-tion includes two mirrors (mounted on the surface samplerboom),, stroke gauges on each Lander leg, a grid on the Lander'stop, ultraviolet degradable coatings, and current-measuringcircuits in the surface sampler.

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Beside3 engineering data, selected images will be takenby the Lander cameras to determine properties of the Mars sur-face such as grain size, bearing strength, cohesion, and eoliantransportability >(how easily surface material is moved bythe wind). Other properties to be examined include thermalinertia (how quickly surface temperature changes) and theultraviolet flux levels.

The bearing strength of the Mars surface will be oneof" the first characteristics determined. Immediately afterlanding, a panoramic picture will be taken that will includethe Lander's number 3 footpad and its impression in the sur-face. This picture,- data on Lander velocity and attitudeat landing, and the amount of leg stroke (compression) willbe used to calculate the surface bearing strength, an importantfundamental parameter. ThM' footpad impression will also givepreliminary data on the cohesion of the surface material.

Early in the landed missinn, the surface sampler collectorhead will eject its protective shroud. Following the ejection,the camera will image the spot where the shroud hits the sur-face, using the boom-mounted mirror (tihe area under the retro-engine), and again photograph the footpad and its impressionon the surface. This image will be analyzed like the one takenafter landing to better define critical surface properties ofbearing strength, cohesion and eolian transportability.

While the surface sampler is acquiring samples for theanalytical instruments, the physical properties investigationwill automatically be acquiring data by measuring the samplermotor currents and taking pictures of the surface markings gen-erated by the sampler. Even the pile of excess sample dumipedby the sampler after giving the instruments all they need willbe of interest to the Physical Properties-scientists.

When the sample for the Gas Chromatograph-Mass Spectro-meter (GCMS) is comminuted (ground) the comminutor motorcurrent will be recorded for analysis by the scientists todetermine grain size, porosity and hardness.

The team has defined several unique experiments to bet-ter understand surface properties. These include diggingtrenches, examining material in the collector head jawwith the magnifying mirror, piling material on the grid atopthe Lander, picking up and dropping a rock or clod on thesurface, pressing the collector head firmly into the surfaceand using the collector head thermal sensor to measure sur-face temperatures.

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-56-Another very simple experiment for the Physical Proper-ties investigation is the addition' of ultraviolet degrada-ble coatings on the camera reference'test charts. Thesecoatings darken in the presence of ultraviolet and theamount of darkening, to a certain limit, is proportionalto the total amount of ultraviolet received.The investigation will provide valuable informationto complement the results of other studies, such as geologyand mineralogy. Know)edge concerning the structure of thesurface can be very helpful in understanding apparently con-flicting data and grasping the, significance of otherwiseunexplainable findings.The Physical Properties investigation team leader 3'sDr. Richard W. Shorthill of the University of Utah.

Magnetic PropertiesThe Magnetic Properties investigation will attempt todetect the presence of magnetic particles in the Mars surfacematerial, and determine the identity and quantity of theseparticles.Iron-in magnetic minerals is usually an accessoryphase in naturally occurring rocks and, surface materials onEarth, on the Moon and in meteorites. The chemical form inwhich this magnetic iron occurs on a planetary surface mayvary from elemental metal to more complex iron compounds(i.e., ferrous oxide magnetite, highly oxidized hematite,the hydrates goethite and lepidocrocite). The abundance andchemistry of the accessory Iron minerals on the surface havebearing on the.-degree of differentiation -and oxidation of theplanet; the composition of its atmosphere, and the extent ofinteraction between the solid surface materials and theatmosphere.This investigation uses a set of two permanent, samarium-cobalt magnet pairs, mounted on the back of the surfacesampler collector head. Each Pair consistq of an outer rn:;,magnet, about the size of a quarter, with an inner core-maqnet of opposite polarity. 'These are keiativply slronnomagnets. (The maximumfield obtained is approximately 2;,500gauss. A gauss is a urit of magnetic field intensity.)

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