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NASA Facts',,Kars as a Planet"National Aeronautics and Spaqe Administration,Washington, D.C. Educational'PiogramsDiv.-

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MP-$O. 83 Plirr.7Postage:.HC Not Available from EDRS.DESCRIPTORS \Aerospace Technology; *Astronomy; Earth-S 'ence;

*Instructional Materials; Science Education;*Scientific\Besearch; *Secondary School Science;-*Space Sciences

IDENTIFIERS *Mars; Solar System

ABSTRACTPresented is one of a series of National Aeronautics

and Space Administration (NASA) facts about the exploratioh of Nars..Photographs, showing Mars as seen from Earth tb\rough a telescope,show dark markings and polar caps.present. Photographs from Mariner7, Mariner 4, and Mariner 9 are included. Presented is a composite ofseveral Mariner 9 photographs that reveal tile .summit craters and thecliffs at the base of a high-pile of lava `with an altitude tracescheme drawn across a mountain dia ram: 4 ex lanation of the changes

.occurrin'gMariner 9describedabove andliquid isinclusion(EB)

on Mrs on the basis of c ose-up o serva ions yis presented. Both the geology and atmosphere of Mars are. A contour nap showing the highest contours j.5 kilometersbelow the level on Mars et which water can exist as aincluded: Student involvement is facilitated by theof three suggested activities and suggested readings.

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An Educational Publi Cabon.of theNational Aeronautics andSpace Adminstration

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,-i-i-MARS AS. A PLANETc=1, One of a series of NASA Facts about the explore- .

Iron of Mars,

Surface Features -of Mars

The first great change in human attitude towardthe planets came in the seventeenth century. Withthe. invention pf the telescope the planets wereseen to have size, they were no longer points oflightilke the stars, but worlds that might be similarto the Earth. The second great change came withthe space age when close inspection of the planets

. by spacecraft changed them from remote anddistant worlds to places that could be explored.

The first record of anyone seeing features on,.the surface of Mars. is that of Christian Huygens,

'a Dutch physicist and astronomer. In 1659 he madearoucjtkatch_'-0

now known as the Syrtis Major ("Great Quick-sands").

The .features on Mars are digi.cult to observewith small telescopes because although Marsapproaches close .to Earth compared with mostother planets of the Solar System, its physicalsize is small: a little more tha,n half the diameter of,Earth. Classical markings on Mars (Figure 1) ap-pear dark grey or bluish green upon a reddish-ocher background with white polar caps-that varyin size with .the Martian seasons.

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Some astronomers Claimed that they could seelinear markings criss-crossing the planet inintricate, geometrical patterns, .marki,ngs whichwere popularly called canals, from the Italian"canali" or "channels." A few, such as PercivalLowellih the last century, believed that these linearmarkings were evidence of intelligent beings onMars conserving water supplies on a dying planet.This :viewpoint was not, however, accepted by themajority of astronomers.

Mars, too, was known to possess an atmosphere._ Photographs taken in ultraviolet light, which does

not, penetrate an atmosphere welt, showed alarger disc to Mars than photographs taken ininfrarQd ht whi h .en- r t

The first major map of Mars was published byWilhelm .Beer and J. H. von Maedler in 1840. Butthis map bears little resemblance to the Martianfeatures now mapped in great detail by NASA'sMars-orbiting spacecraft, Mariner 9.

Before this spacecraft produced detailed pic-tures of Mars, controversy raged fortmany yearson the nature of the illusive Martian markings;especially since their intensities and shapes ap-peared to vary with seasons on Mars. And.anothergreat controversy raged on the nature of the sea-sonal polar caps as to whether they were of iceand snow like Earth's caps, or of frozen carbon'dioxide.

face. Moreover, astronomers often observed lightmarkings., and, hazes' which they interpreted asclouds.and dust in the-atmosphere of Mars.

The first spacecraft to reach Mars, NASA'sMariner 4 (1965), provided only-e limited numberof telescopic close-ups across the Red Planet.None of the familiar markings that astronomerssee from Earth could be identified. But many ofthe pictures showed craters similar to those onthe Moon. Many scientists erroneously concludedthat Mars was a moon-like body; its surfaceshattered and splattered by the impact of largebodies falling,from. space; some the size of smallmountains. A few pointed out, however that therewas evidence of linear features on Mars (Figure 2)that could be faults such at those that. borderrift valleys on Earth, and that these might beevidence of vulcanism on Mars.

Subsequent NASA spacecraft, Mariners 6 and7 (1969), again revealed heavily- cratered terrain,hut with some unusual features that were difficultto explain if the Martian surface had been formedsolely by the impact of large meteorites;In places,Mars seemed to have collapsed inwards to pro-duce complex patterns of fractures and slumpedterrain. Additionally, these pictures revealed that

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Figure 1. Mars as seen from Esith through a leisscops shows dark markings and polar caps. Thesl yary with the seasons onMars. This sides of Mariner 7 pictures' shows rotation of' Mars at about the same resolution. '

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thepol ps,probably consisted of thin carbon-clkod e snow which disappears quickly, but with

2a.pennanent ice cap over a much smaller areaof of each polar region. Peculiar. ridges near the

poles_suggastad that the ice caps may be layeredwith dust

In 1971 Mariner 9 went into orbit ardund Marsand began a detailed photographic survey of theMartian surface. The first pictures were disappoint-ing. Mars showed a uniform, image resembling an

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old tennis ball with no visible details except fora faint polar cap. The spacecraft had arrived whenMars was engulfed in a monstrous wind stormwhich shrouded the whole of the planet, 'with cloufsof sand and duit (Figure 3).

The storm had,started in regions called Helles-pontus and Noachis in the sOutbarn hemisphere,and then spread rapidly to engulf all the planet. Asseen from Eattli, detailed markings on Mars

jaded. As seen from Mariner 9, the yellowish cloud

" Figure 2. The first spacecraft (Marinir 4) to arrive at Mars, showed large eaters but 240 hinted at volcanic acth4ty by the -presence of a lineament cutting diagonally across the bottom right-hand corner of. the picture.

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obscured everything, except for the *south polycap and four dark 'spots. .

Intense dust' storms had also been observed onMars. in 1892, 1924, 1941, and 1956, and later in1973. Each engulfed the planet when Mars wasat its closest to the Sun (perihelion). It seems that

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major storms may occur each year on Mars, butare not so easily observed from Earjh when Marsis not at the close (perihelic) oppositions.

elradually the 1971 storm cleared and a groupof huge volcanoes was seen, their cratered peaksprojecting rifiles'abOve the settling dust fn sub-

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Figure 3. When Mariner I arrived at Mars in 1.71 the planet was shrouded in duit and only the south polar cap and, four darkspots were visible.

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sequent months a completely new interpretationof the Martian features had to be accepted. Marscould not be considered a dead world. About half'of the planet's surface is Very old and heavilycratered, much like the highlands or the backsideof the Moon. The other half is. younger terraincontaining the biggest volcano known and theequivalent of ocean basins, fractured and over-,lain with sedimentery and wind-borne deposits.

. The big volcano (Figure 4) is seen from Earthas a light spot on Mars. It was called Nix Olympica(Snows of Olympus) but has.baeruenamed Olym

pus Mons (Mount Olympus) since it is holirkti-ownto be a mountain, the highest feature on Mars.Olympus Mons peaks at 25 kilometers (15 miles)above the surrounding plains.

About a score of large volcanoes have nowbeen identified on Mars. It is speculated that notvery-long ago.the fiery glow of lava may have filledmany of the caldera craters in the throats Of thesehuge Yolcania---piles..And.there is nothing to dis-prove that these volcanic fires might still be burn-ing, with eruptions taking place. again in years to

MMINEMLIS

come. Even. on Earth, volcanoes often- remaindormant for centuries between eruptions.

Another newly-discovered feature on Mars is aunique super Grand Canyon that stretches acrossthe planet a distance equal to the width of theUnited States. The, canyon (Figure 5) is 120 kilo-meters (75 'miles) wide and 6 kilometers (4* miles)deep. Its wane show evidence of erosion as thoughstreams of *water have flowed into it from theSurface and from underground sources. Also at itseastern end the material that was_washed from Itappears to be deposited in great plains extending

.northWard toward the pole.

Violent winds may cut through the canyon andits many tributaries as the, r,esult"of temperaturedifferences along them asAhey straddle the daynight boundary called the `terminator. Winds- in 943thin atmosphere of Mars must reach as high as320 kilometers per hour (200 m.p.h.) to raise theplanetwide dust storms..

-Mars also' has giant dust bowls,' -.old impactbasins, gbuged 'out 6y- mountain-sized objects

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crashing into Mars, and now filled with dust erodedfrom the Martian highlands and continually stirredby winds that whirl endlessly within the basins.

Equally as surpOsing, sinuous channeld werediscovered on Ma94, They look as though, they aredried up. river beiteequal in size to the AmazonRiver with elearly4efined banks and intertwiningSandbars, some with veined patterns of tributaries.The presence-of such. features came as a com-plete shock since scientists had concluded that_

'water could not flow in large quantities as a liquidor Mars; the temperature is too low and the atmos%pheric pressure too low. And yet, if the erosionfeatures have been made millions of years agowhen conditions on Mars were very different from

'today, the big question is why the channels are sofresh looking. It would be expected that the violentannual dust , storms would cover the charinelswith drifting sand -and dust.

There may be extensive layers of permafrostall over Mars, as-in the northern tundra of Earth.If such an area of permafrost were, suddenlymelted by volcanic activity, flash floods could beproduced to wash out the channels. Such meltingof permafrost might also account for the peculiarareas of slumped terrain which dot some regionsof Mars.

The quantity of water still readily accessible atthe surface of Mars is unknown. The quantities ofcarbon dioxide (in the atmosphere and. the polarcaps) suggest that there must also have been much

'water at one time on the planet, since wailer andcarbon dioxide are both vented by active vol-canoes. On 'Earth this water has remained andforms oceans, while the cprbon dioxide wastrapped into carbonates in the Earth's crust. It,could very well be that Mars still retains its'wateras ice, both generally3 in the ocean basins andespecially in the polar caps where they may becovered with alternating laydrs of dust and ice.The core of each polar cap might, be ice severalmiles deep which has depressed the crust of Marsat the poles by itsiweight. The extensive seasonalcaps are believed to be'thin caps of frozen carbondioxidewhich disappear in summer. Mariner' 9showed that much smaller caps, probably of ice,do not disappear in summer on Mars.

There is Still evidence of ancient ruined.cratersin the polar regions, but generally they show alaminated young terrain in whicti:dust and ice mayhave accumulated over millions of years in distinctlayers like stacked dishes. Edges of the stacks arcaround each pole. These laminations seem to betoo big to be yearly features. Rather they suggestlong term climatic" fluctuations on Mars whichpccur every 50,000, years or so.

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Figure t. Violent winds scream across the surface or Mars,creating dust storms and making wind-blown markings suchas these streaks from Martian craters. These wind-depositedpatterns cover large areas and cause changes to the surface -rthat are observable from Earth and-were-once thought to becaused by growth of vegetation on Mars.

Explaining Changes ontMacsThe classical variable features on Mars, at one

time explained as a seasonal groWth of vegetation,can pow beobservationsthree general'

w_cplained on the basis of close-upNASA's Mariner 9. They are ofesa uniform enhancement of

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contrast, irregular dark markings, and bright and'dark areas that develop during- the Martianseasons.

The uniform enhancement of contrast takesplace when dust storms dissipate in ei..effectsimilar to a ,city skyline gradually comaingclearer as morning mists disperse with a risingsun. SplotcheS that appear on Mars are irregulardark markings that relate to the surface featuresof hills, valleys, and craters. They do not changegreatly except to become indistinct when duststorms enshroud them. Finally, We bright and ,dark streaks that develop during Martian seasonsappear to be the result of removal or deposit ofwind-blown dust along characteristic wind patternsthat repeat year after year. They are associatedwith the classical dark features of Mars which -have been observed for centuries from Earth:Seenclose-up in the space probe phdlographs they aremade up of many smeller areas, often in thebottoms of craters and sometimes spilling over thecrater wails into, the surrounding territory and

`alongside ridges or scarps.

While it is generally accepted that the darksplotches on Mars, may result from wind-blowndust, some close-ups of craters reveal a sand-

. dune type of surface forming the dark splotch.Thus they are most likely sand dunes. But therehas been speculation that the splotches could re-.

suit from Martian vegetation growing selectivelyin areas protected from the Martian winds anddust. This would apply especjally to those dark,markings close to ridges and remnants of craterwalls.

Other dark areas are resolved into complexsystems of streaks associated with craters, liketails of comets (Figure 7). Other streaks are, how-ever, of bright material also emanating from cra-ter§. On Syrtis Major, The prominent, triangular-shaped marking mapped by Huygens, there areboth dark and light streaks criss-crossing eachother as though dark and light material has beendeposited by complex winds. Variations in SyrtisMajor are observed from Earth and may be theresult of seasonal winds which first produce lightstreaks inane direction and then later dark streaksin another, direction. Since Syrtis Major has beenrevealed as a region of very steep slope fromhighlands to an ocean basin, some winds may blowalong the slope and others up and down it.

Bright'streaks may originate from the fine dustof. a major dust storm which collects in crater

bottoms and is later blown from the crater by highwinds. The dark streaks may be caused by 'otherwinds later removing the light material from anunderlying dark terrain. The,evidence today points .toward the transport of light material by winds asthe major cause of the changing appearance of.Mars as seen from Earth.

Geology of Mars (Areology)As pointed out earlier, the pictures returned from

Mariner 9 reveal that Mars' surface has beenmolded not only by impacts but also by volcanic,tectonic, erosion, and sedimentary deposits(Figure 8). The moon-like areas are 'mainly in thesouthern hemisphere and mid and high latitudes.There are alstv some mare-type circular basins in

the southern hemisphere which have been filledwith smooth material. These seem to be old andconsiderably changed since their formation.

The evidence to date implies that , Mars hasdifferentiated, le. partly melted after its originalformation, with the result that low density materialsrose to font a crust and heavier materials sankto form a cores This is confirmed by. the chotparticles which are known to consist predominantlyof silicon dioxide, showing that the loW density

. materials must have risen to the surface of Mars.The thick covering of dust is most probably

/powdery with/consistency Of talcum.

( Large parts of the northern hemisphere of Marsconsist of smooth plains with very few craters

on them. They are like ancient ocean bottoms,.

lapping against higher land nearby. Also in thenorthern hemisphere there are four monstrousshield volcanoes that have steep-sided domeswith cratered summits. Shield vol es are builtAlp by repeated flows of lava that -ov. millions of

pile up in sheets sloping y-;from thecentral crater. Widespread effects of vulcanismspread from the volcanoes as multiple lava flows,ridges, chains of craters and sinuous rilles. /

/ The several volcanic regions on Mars appear tobe connected with a general doming of the crustin the area, surrounded by extensive fracturing ofthe crust. The most extensive fracturing spreadsover a -large part of the planet from the Tharsisregion where most of the big volcanoes are lo-cated. The great Valles Marineris, the .GrandCanyon of Mars, seems to be a radial feature fromthe Tharsis doine.

Elsewhere on Mars there are,exatfiples of wide-spread crustal deformation; scarps, graben, faults,and 'mosaics of flat-topped blocks of crust. Thereare regions of chaotic terrain which consists. ofan intricate mixture of broken and jumbled blocksof crust. But 'there are no oompressional scarpsas seen on Mercury. Nor, is there clear evidenceof the motion of crustal plates as on Earth.

Mars thus emerges as a complex planet with ahistory very different from the Moon and Mercury,perhaps displaying an evolution between .theseplanetary bodies and the Earth. .

The Atmosphere of AfarsScientists long disputed about the atmosphere

of Mars. Before the space program a century Ofwork based on observations from Earth had pro-vided very little information abciut the atmosphereof Mars other than the presence of carbon dioxide,and traces of water vapor. The most commonlyquoted value for the surface pressure of theMartian atmosphere was that determined byDollfus, of85 millibars, i.e. 8.5 percent of the pres-sure at- sea level on Earth. This was equivalentto the pressure at 50,000 feet high in Earth's atmos-phere; higher than most commercial jets fly.

However, when NASA spacecraft reached Marsnew information about the planet's atmospherebecame available and the results were not en-couraging from the standpoint of life on the RedPlanet. Surface pressure in the near equatorialregions of Mars ranges from a high of 0.89 percentof Earth's sea-level pressure in Hellas (a verylow region), to a low of 0.28 percent 'in Tharsis (ahigh region of Mali). At high northern and southernlatitudes pressures between 0.72 and 1.03 percentof Earth's sea-level pressure'have been measured.

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Figuie S. This most modern map of markings on Mars shows them in relationship to the geologic features revealed bythe photogiaphs taken by Mariner 9 in orbit around Mars for many months during 1971.

IThe pressure. is very important since, taken in

conjunction with the temperature, it determineswhether or not water can exist as a liquid. Atlbw pressures, water changes from ice to vaporwhen heated and doesjlot pass through the liquidstate believed essential to life. Clouds in theMartian atmosphere uggest the presence of watervapor and ice crystals as well as crystals of, carbondioxide. Cloud structure also shows downwind(lee) waves of craters generated by an east-to-west flow of the atmosphere. There are also thinhaze layers above the loweratmosphere, seen inNASA pictures of the limb,of the planet. These maybe hazes of carbon dioxide and water ice crystals.Some limb hazes are also caused by dust clouds.

Clouds also make up the polar hoods whichcover the polar cap areas in winter and are edgedwith weather systems similar to cyclones andcold fronts on Earth. As these storms dissipatecloser to the cquatoor their high winds produceregional dust sforms.

On the high volcanic mountains 'clouds formeach afternoon, and low mists surrourid the basesof the mountains at times. These are thought tobe water clouds; possibly water vapor is still beingexuded by the volcanoes. For yea,rs, Earth-based,astronomers saw the neighborhoods of these vol-canoes brighten in the afternoon. The brighteningsare now known to be the result of the afternoonclouds which have been recorded in many photo-.graphs from Mariner 9.

Temperatures on MarsThe temperature of the Martian atmosphere at

tilt surface is between 23°C (-10°F) and 3°C(26°F). But this temperature is dependent upon theamount of dust in the Martian atmosphere. The

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temperature of the surface itself behaves some-what differently film that of the atmosphere. Themaximum surface' temperature occurs each daynear the, latitude of the 'point on the surface ofMars where the sun shines 'rectly overhead, butat about one hour after loc I noon, irrespectiveof whether the atmosphere is dust filled or not. '''

Maximum atmospheric temperatures were meas-tired by Mariner 9 late in the afternoon near latitude60 degrees south during the dust storm of 1971,but as the dust cleared the atmospheric tempera-ture maximum movedtcriuoiriadervarthe pose- ,tion of the surface temperature maximum.

Generally, conditions on Mars were found byMariner 9 to be less harsh than previously thoughthigh enough atmospheric preasures in low lyingregions for liquid water to be present at ,times;temperatures rising to 27°C (80°F) at local noon.

Pressures suffitierit for water to exist as a liquid,i.e." bove 6.1 millibars, occur during summer inlarge areas of Agyre, the western MargaritiferSinus, 'Isidis Regio, and Hellas, and in a greatbelt circling the northern hemisphere between 40and 50 degrees where there are several big valleys.

Mars as a Planet Today.In the telescope, Mars appears as a map fuzzy,

disc, reddish in general color, with greyish-greenmarkings and topped by white polar 'caps. Marsis about half Earth's diameter with a gravity atits surface about one-third that of Earth. A 100pound student on Earth would weigh. only 38poLinds on Mars.

Tem'peratures on the surface generally reach0°C (32°F) in early afternoon with some areasreaching 27°C (80°F). At night the temperatureplunges to a frigid 123°C (-190 °F).

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It seems that Mars may be a planet that haspartly made the transition from a moon-like bodyon which the surface was molded by impact ofinfalling bodies some 4 billibn years ago, to avolcanically-active, water-dominated body suchas the Earth. Extensive tectonic activity haschanged large regions of Mars, pushing up domesof the crust and producing long linear, faults. Ad-ditionally huge volcanoes have covered extensiveareas with lava relatively recently in fhe Martianhistory.

The planet's surface has been eroded and sedi-ments have been deposited over other vast areas.Channels tran ported enormous quantities of ma-.terial from o e part of Mars to another, just asrivers carry ma ial from Earth's continents into

_ the ocean basing. The only feasible explanation isthat water has been generated in surges on Marsin sufficient quantities to wash the channels, onlylater to become locked in permanent ice or to belost in space.

The possibility of life on Mars has again beenraised because of. the obvious water erosion andthe pressures existing in low lying regions whereliquid water could be present even today. Andthere could be evidence of fossil life from thetime'when water was more plentiful on Mari.

Thus the excitement of possibly finding life e lse-where in the Solar System Is again stimulatingscientific resbarch to mount a new expedition toMars that will land.upon the planet's surface. Thisis Project Viking of the National Aeronautics andSpace AdministratiOn, an unprecedented explore-.tion of another, world scheduled to start on the200th anniversary of the founding of the UnitedStates.

VUDENT INVOLVEMENTProject One

On the deorogic map of Mars shown in Figure 8,superimpose the contours of Figure 9. This willshow, you where the lowest areas /e on Mar,s.These are the areas where liquid water can todayexist even in .the rarefied atmolire of Mars.Identify on your map, by shading r.color, whereyou would land an expedition to search for lifeon the red planet. Make a table listing the nameof the area, its latitude and, longiturg-its charac-

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teristics (cratered, plain, mountainous, valley). Ifyou have only two opportunities to land a space-craft on .Mars which of these Aeveral areas wouldyou pick, and why?

Project Two' Make a list of the unknowns about Mars that youwould like to solve with a spacecraft that couldland on Mars. What sort of experiments would youplan to solve your questions about Mars? Describethe equipment they would use, such as cameras,surface samplers, chemical analysis.

Project -ThreeUse the information in Figure 4 to make a plan

map and a cross section of Olympus Mons on a*scale of twct inches to a hundred miles horizontallyand one inch to 10 miles vertically. Refer to agood atlas and make a similar map and ,crosssection of the main island of Hawaii on the samescale, including parts of-this big shield volcanothat are underneath the ocean surface. You willsee the relative sizes of the biggest volcano onEarth and the biggest volcano on Mars. Scientistsbelieve that the plate of Earth's crust carrying theHawaiian Islands has moved, steadily over a plumeof hot magma coming from the Earth's mantle; soinstead of building one big volcano as on Mars,this plume of lava has built up a series of islandacross the Pacific Ocean. Try to estimate how bithe.yolcanoin the Pacific might have been if thematerial had not been spread out into the longchain of the Hawaiian Islands. Would it have been--as big as Olympus Mons on Mars?.

Suggested Reading

THE NEW MARS; W. K. Hartmann and 0. Raper,NASA 'SP-337, 1974, -U.S. Govt. PrintingOffice Stock Number 3300-00577

MARS FROM MARINER 9, B. C. Murray, Scientific,American, v. 228, n. 1, January 1973, pp.'48-69

MARINER 9 JOURNEY TO MARS, K. F. Weaver,National Geographic Magazine, v. 143, 2,February 1973, pp. 230-263 :

MARINER 9, MARS 2 AND 3 MISSIONS, Variousauthors, Icarus, v. 17, n. 2, 'October 1972,entire issue.

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