Images of Mars the Viking Extended Mission

8/8/2019 Images of Mars the Viking Extended Mission

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C.'


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NASA SP-444

IMAGES O F

M A R SThe Viking

ExtendedMission

Collected byMichael H. Carr

U.S. Geological Surveyand

Nancy EvansJet Propulsion Laboratory

NASAScientific and Technical Information Branch1 980

Nation al Aeron autics and Space Adm inistrationWashington, DC


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For sale by the Superintendent of DocumentsU.S. Government Printing Office, Washington, D.C. 20402


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Foreword

Images from one of the mostextraordinary of NASA's space mis-

sions are presented in this book. TheViking mission t o Mars was conceivedin 1968, and two spacecraft werelaunched to the planet seven yearslater. Viking 1 was scheduled to landon the Martian surface on July 4, 1976,the Nation's bicentennial, but, becauseof the unexpected rugged appearanceof the originally chosen site , landingwas delayed until July 20, 1976, the

seventh anniversary of the first mannedlanding on the Moon. Since that timeth e two Viking landers and two orbitershave returned a n enormous amount of

information about the planet. Thespacecraft were designed to operatefor only 90 days, and initial expecta-tions were that the spacecraft mightlast only a few weeks. No one couldhave predicted that at this time o ne ofth e two orbiters would still be operat-ing, sending back pictures to Earth,and that both of the landers would stillbe operational. It is even now hard tocomprehend that one of those landersmight continue to operat e for ten yearsor more.

The photographs and the textsin this volume provide a n elegant lookat the planet Mars as revealed by Vikingduring its extended mission. Some of

the pictures were taken as recently aslate 1979 and are therefore of particu-lar interest.

Thomas A. MutchAssociate AdministratorOffice of Space Science

March 1980


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Overview of Mars

Mars, named after the Romanwar god because of its angry, red ap-

pearance in the night sky, has beenknown to man since prehistoric times.It is the fourth planet. from the Sun,after Mercury, Venus, and Earth. Likethese planets it has a mostly solid sur-face, in contrast with the outer planetswhich ar e composed mostly of gas.Mars is just slightly more than one-halfas large as Earth, having a radius of3393 km (2108 miles). The Martianday is just over 24 hours long, but theyear on Mars is 687 days or 1.9 Earthyears. The two moons of Mars werediscovered in 1877 by Asaph Hall, and

named by him Deimos (Terror) andPhobos (Fear) after the two attendantsof Mars. Phobos, the inner and largersatellite has a diameter of 2 4 km (15miles) and circles Mars every 7.6 hoursa t an altitude of 6000 km ( 3700 miles).Deimos is 12 km (7.5 miles) acrossand circles the planet every 1.3 days atan altitude of 24 000 km (15 000miles).

The canals discovered bySchiaparelli in 1877 and described bymany observers since that time havenot been identified as such in images

returned from various spacecraft. In-stead, the planet has been revealed tobe extraordinarily diverse in both geol-ogy and meteorology.

Huge volcanoes suggest sus-tained activity that appears to havecontinued up to the present day. Gi-gantic floods have flowed across thesurface periodically, deeply. scouringthe terrain and cutting large channels.

There are also smaller channels in-dicative of slow erosion by runningwater in the manner that terrestrialriver valleys form. The channels arepuzzling because liquid water cannotexist on the Martian surface under pre-sent conditions; it would either freezeor rapidly evaporate. The channels,therefore, suggest different climaticconditions for the past. Huge canyonsindicate faulting and land sliding on agrand scale, while layered deposits atthe poles suggest sustained cyclicsedimentation. Although no liquidwater is at the surface, considerableevidence exists for ground ice, belowwhich liquid water could be present.Most impact craters ar e surrounded byflow patterns that indicate that thematerial ejected had a mud-like con-sistency, as i f the impact hadpenetrated the permafrost layer to ex-cavate the water-rich material frombelow.

Since the rotation axis is in-clined 25", th e planet has seasons justlike Earth. However, the eccentricity ofthe orbit around the Sun causes theseasons in each hemisphere to be ofunequal lengths and intensities. Thesouth has short, hot summers andlong, cold winters, whereas the sea-

sons in the north are less extreme.

The Martian atmosphere isthin, approximately one one-hundredththat of Earth, and consists primarily ofcarbon dioxide. Polar caps, also com-

posed of carbon dioxide, advance andretreat with the seasons. It is thoughtthat the carbon dioxide migrates frompole to pole between th e winter seaso nfor each hemisphere. So much of theatmosphere condenses in the polarcap formation that the atmosphericpressure may drop one-third in theprocess.

Temperatures have a wide dailyand seasonal variation. Polar tem-peratures during the winter may reachlows of -140" C (-225" F), whereasnoonday temperatures at the equator

may reach 20"C

(68" F). Surfacetemperatures at the Viking Lander 1site have been noted to vary approx-imately 75" between predawn andmidafternoon measurements duringsummer in the north. Temperaturesranged from a low of -88" C (-158" F)to a high of -12" C (-21" F).

For most of the year the atmos-phere is relatively calm, with windspeeds rarely exceeding 5 mlsec (1 1mph); however, during the southernsumme r violent storms develop whichcan result in winds in excess of 5 0

mlsec (1 10 mph).As Viking approaches its anni-versaries of arrivals and landings onMars, one of each in July and Septem-ber of 1976, this booklet presentssome of the phenomena that havebeen observed during th e 2 Mars years(4 Earth years) of operation.


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Mars has enormous volcanos,most of which are in the region ofTharsis. Olympus Mons, pictured here,is 27 km high (17 miles) and sur-rounded by a circular cliff 500 km (300miles) across. Close-up pictures of thecliff show lava flows draped over thecliff an d extending far beyond it so thatthe volcano is actually about 700 km(430 miles) across. By comparison th elargest volcanoes on Earth, those inHawaii, are 120 km (75 miles) across a ttheir bases on the ocean floor. Thelarge,Martian volcanoes strongly re-

semble those in Hawaii in that theyhave large summit craters, long thinflows, lava channels, and lava tubes.The resemblance is so strong as tosuggest similar basaltic compositionfor the lava. Many parts of OlympusMons are devoid of impact craters, in-dicating a very young age. Indeed thevolcano may still be active, althoughthe t ime interval between eruptions isprobably long. The large size suggeststhat it has been active for at least abillion years.

Figure 1

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Around the volcanoes and inseveral other areas of the planet arevast lava plains similar to those of thelunar maria. Individual lava flows maybe hundreds of kilometers long andcover thousands of square kilometersof the surface. Shown here is a high-resolution view of superimposed lavaflows. On the surface of the flows ar eparallel ridges that probably formed asthe cooler upper parts of the flowmoved along and crumpled. The edgeis marked by a cliff approximately 30m (100 ft) high. Bright dust has ac-cumulated at the base of the cliff,probably as a consequence of windduring planetary dust storms. The areashown is 12.5 km (8 miles) across.

Figure 2

On some volcanic plains aremany small volcanic cones. This viewof lsidis shows numerous low mounds

with summit pits, many arranged inlong lines. Most of the mounds areabout 500 m (l/3 mile) across. They re-semble terrestrial spatter cones andspatter ramparts that accumulate fromglobs of lava that have been thrownout from a volcanic vent. The aline-ment of the vents probably reflectsfaults in the surface below the volcanicmaterials. Why some plains are cov-ered with spatter cones and othershave large lava flows is not known, butit may be connected with the rate atwhich the lava is erupted, with large

eruption rates causing flows andsmaller eruption rates causing cones.Another possibility is that the lava thatformed the cones seen here was moreviscous than the lava that formed theflows shown in the preceding picture.

Figure 3


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Figure 4

An old faulted surface (to the The faults are believed to be the resultright) is embayed by younger smooth of deformation caused by the weight oflava plains (to the left). Near the center the large bulge in the Martian crustof the picture is a small volcano 4 km centered over Tharsis. The area shownacross with an elongate summit vent. is 58 km (36 miles) across.In this area , called the Tempe Plateau,such small volcanoes are relativelycommon and contrast sharply with thehuge shield volcanoes in Tharsis to th esouthwest. Most of t he small volca-noes are situated on faults similar tothose which form the cliffs to the right.


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A puzzling feature of the Mar-tian surface is its large channels. Manystart full size, with no tributaries, andhave many characteristics in commonwith large terrestrial flood features.So me are of such e normous size thatdischarges of more than 10 000 timesthe normal discharge of the Amazonare implied. Here you see one of the

largest flood features, Kasei Vallis, inplaces more than 30 0 km (18 0 miles)across. The ground is deeply scouredwhere tear-drop-shaped islands haveformed around obstacles such as

craters and low hills. .The flood appar-ently swept northward and then turnedeastward as it converged on somedeeply incised channels. The high-resolution view shows a part of thechannel floor. The scoured surface ha sbeen deeply dissected either duringth e waning stage s of the flood orsubsequently by some other process

such as wind erosion. The detailedimage is 30 km (18.5 miles) across.

,The height of the cliffs is not knownbut probably exceeds 1 km (3200 ft).

Figure 5

Figure 6


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Figure 7

So me large channels start near channels are unknown o n Earth. Alter-volcanoes. The ones seen here start natively, the channels might have beennear the large volcano Elysium Mons cut by water released from the meltingand wind their way to the northeast for of ground ice during volcanic erup-several hundred kilometers. In this tions. The area shown is 180 km (1 10case flow has been restricted to dis- miles) across.Crete channels, unlike the flow thatscoured broad a reas and formed KaseiVallis. Apparently the fluid repeatedlyoverflowed the banks to form a com-plex array of interconnected channels.The origin of these channels is contro-versial. Because the channels start sonear a volcano, they could be lavachannels, although such extensive lava


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Slow erosion may have formedthis channel by a process similar to t hedevelopment of terrestrial river valleys.This kind of channel is characterizedby well-developed tributary systemsand is very common in the older ter-rains. Nirgal Vallis, seen here, is one ofthe largest of this type, more than 5 00

km (310 miles) long. The tributary net-work is very open; the individualbranches a re deeply incised, with ste epwalls, and the areas between thebranches are undissected. These char-acteristics suggest that the channelformed by ground water sappingrather than by surface runoff. The

water could have been derived fromground ice or from water beneath apermafrost layer. In either case, moretemperate climatic conditions thanthose which presently prevail are im-plied. For scale, the high-resolutionimage shows an area 8 0 km (50 miles)across.

/ igure 8

Figure 9


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Close to the equator betweenlongitudes 40" W and 100" W is a vastsystem of interconnected canyons,called the Valles Marineris. The westend is close to the summ it of a broadrise in the Martian crust termed theTharsis bulge, which rises 7 km (4.5miles) above th e surrounding terrain. Itis on th e northwest flank of this bulgetha t most of the large volcanoes aresituated. The canyons extend down the

'east side of the bulge for about 4500km (2800 miles). Individual canyonsare as much as 200 km (120 miles)across and in the central section,where there ar e three parallel canyons,the system is 600 km (370 miles)across a nd over 7 km (4.5 miles) deep.Ju st visible in the left half of the pic-ture o n the south wall of the main can-yon are tributary canyons. These arethe sa me size as the Grand Canyon inArizona. To the east the canyonsmerge with chaotic terrain which inturn merges with several large floodchannels. The precise way in which thecanyons form is not known, but it isthought to be a combination offaulting and erosion.

Figure 10


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Figure 11

Looking across the canyon,the far wall rises more than 3 km (2miles). A faint horizontal layering inthe rocks exposed at t he top of t he wallwas probably caused by lava flows.Below the rocky upper ledges are .longtalus slopes that reach down to the flatcanyon floor. The fan-shaped featureon the floor is the edge of a large slide.


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Figure 12

Many large flood features startin what has been called chaotic terrain.In these areas the ground appears tohave collapsed t o form a chaotic array

of jostled blocks at a lower elevationthan the surrounding terrain. Channelsemerge full scale from these regions a sthough th e water had come out of th eground and then t he ground collapsed.This high-resolution view shows thejostled character of the terrain. Thearea seen here is 30 km (19 miles)across and the view is oblique with alow illumination; this gives the blocksa pyramidal appearance. Areas ofchaotic terrain can also be seen at lowresolution in the right si de of figure 10.


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Terrain pockmarked withcraters is seen in the high northernlatitudes. The uncratered areas aredark whereas the areas around cratersare light, giving the area a mottled ap-pearance. Presumably the bright mate-rial has been excavated from below thedark, near-surface layer. Here you seea slightly different ejecta morphology.

The craters are surrounded by an innerring of ejecta tha t does not appear tohave flowed as freely as the outerejecta. Possibly at these high latitudesthe colder temperatures inhibit theflow process, perhaps by creating athicker permafrost. The area shown is30 0 km (190 miles) across.

Figure 14


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Figure 15

The wind has extensively modi-fied the surface of Mars through botherosion and deposition. At large scale,the effects of wind are not obvious-other processes such as volcanisril,faulting, and water erosion appear todominate. At finer scales, however,eolian landforms become more com-mon; in the pictures having the highestresolution, those taken with resolu-

tions close to 10 meters, eolian fea-tures predominate. Here you see alarge dune field. in the upper half a reseveral isolated crescentic dunes indi-cating wind coming from the lowerleft. The crescentic dun es merge to t heleft with a large array of transversedunes alined at right angles to thewind. The area shown is 60 km (27miles) across.


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Th e dunes seen in this high-resolution view have been elongated inthe direction of t he wind. One poorlyunderstood aspect of dune formationon Mars is the origin of the sand-sizedparticles. Most of the material found atthe Viking landing sit es and that blownaround the planet in the global duststorms is extremely fine grained and

could not form dunes. The mechanicsof dune formation require the particlesto bounce along the ground, whichdust cannot do . It has been suggestedthat the particles stick together elec-trostatically or are bound together inice to form the required sand-sizedgrains. The area shown is 20 km (12miles) across.

Figure 16


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Wind features are especiallycomm on around the edg e of OlympusMons, possibly as a result of large top-ographic perturbations of th e general,planet-wide circulation system. Thisfluted pattern southwest of OlympusMons occurs in an area where theground appears to have been locallyetched to form hollows, probably by

the wind. The area shown is approxi-mately 20 km (12 miles) across.

Figure 17


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Figure 18

An old plateau area has beendeeply dissected by some unknownprocess. Wind-blown debris has appar-ently accumulated in the valleys andformed strings of dunes transverse toth e length of the valleys. The uppersurface of the plateau h as a roughsandpaper texture that may also be t heresult of wind action. The area shownis 12 km (7.5 miles) across.


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Figure 79

Late in th e extended mission,Viking acquired contiguous high-resolution coverage of a broad swathof old cratered terrain. This is oneframe (42 km, 26 miles, across) ofmany hundreds in that swath. Thescabby appearance suggests etchingof a horizontally layered surface, prob-ably by the wind. The layers appear tohave filled craters: when the layers

were partly eroded away, raised plat-forms were left within some of ,thecraters. The cause of th e layering is notknown. It is perhaps a result of windaction but depositional in nature.Recurrent episodes of deposition anderosion by the wind in this area mayrecord climate changes of th e past.


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Figure 20

Both poles have caps that ad-vance and recede with the seasons.The seasonal cap consists largely 'ofcarbon dioxide but the residual capthat remains during the summer maybe water-ice, at least in the north.Large amo unts of water were detectedover the north pole during northernsummer but not over the south poleduring its summer. This is an oblique

view of the residual northern cap. Atthe t ime it was a little more than 1000km (620 miles) across. The dark linesare mostly valleys or southward-facingescarpments that are free of frost. Thecause of the pattern is not known, butit may be the result of erosion by windsspiraling out from the poles.


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The residual northern cap isshown in detail here. Th e scene, whichis 90 km (56 miles) across, is difficultto visualize because of the confusingeffects of the frost. The bright areas arefrost covered and the dark areas aremostly frost-free. A fine pattern ofstriations is seen in most of the darkerareas. This is caused by layered

deposits that underlie the frost, caus-ing a fine terracing of the darker slop-ing ground. Similar deposits occur atboth poles, extending outward a littleover 10" in latitude from the actual

pole. They are believed t o be a mixtureof dust and ice that h as slowly accumu-lated over many years. Differences be-tween successive layers are probablythe result of variations in dust stormactivity. Such variations would affectthe amount of dust in the atmosphereand hence the amount deposited a t thepoles. Thus the layering is a record ofclimatic variations in the recent geo-logic past. The layered deposits arerelatively young, as indicated by thelack of superimposed impact craters.

Figure 21


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The layered deposits at thenorth pole are never seen without thediscontinuous frost cover of the rem-nant cap. However, in the south theremnant cap is smaller so that much ofthe layered deposit is unfrosted insummer. In this picture, the smoothlayered deposits clearly overlie anolder cratered terrain partially filling a

crater (lower right). The smooth mate-rial appears to have flowed into thecrater, a s might be expected of ice-richsurfaces. This is somewhat conjec-tural. The lack of craters in the smootharea is striking. The area shown is 200km (124 miles) across.

Figure 22

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Figure 23

Figure 24


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Since all the surface area sur-rounding both landers was photo-graphed by the end of 1976, laterstudies concentrated on searching forchanges in the scene. The picture tothe upper left, taken in August 1976,has been included to show the sc ene a sit looked then. Change A, the latestchange to be identified, occurred be-tween September 16 and September20, 1978. It is believed to be a small-scale slide of an unstable dust layerand appears as a small circle-like

formation downwind of Whale Rock.Change B, pictured in the lower left,which occurred early in 1977, shows asimilar formation near Big Joe, muchcloser to the lander cameras. It is nowbelieved that the dust layer that coversthe surface is regularly redistributedduring periods of high wind.

Figure 25

During the northern autumn,the polar cap grows to considerablesize, but the process cannot be ob-served because it occurs beneath thedense carbon dioxide cloud covercalled the polar hood. The cap con-denses out of this hood an d as more

carbon dioxide is removed the planet-wide atmospheric pressure falls. Meas-urements of this pressure drop madeby both landers were used to deter-mine the volumes of carbon dioxideremoved from the atmosphere. Thisfigure divided by the areal extent of the

ca p (estimated to extend down to warmed by the Sun , volatilizes rapidly,60" N) revealed the polar ca p to be leaving the dust and water-ice thatseveral ten s of centimeters thick. Dur- have remained on t he surface foring the past two northern winters, how- about 100 days each year.ever, a thin coating of water-ice hasbeen observed at the Lander 2 site at43" N. This covering, seen as light

patches on and to the shaded side ofrocks, is estimated to be 0.002 centi-meter thick and is invisible from theorbiter. Water and carbon dioxide arethought to condense on dust particles,building up sufficient mass to settl e tothe ground. The carbon dioxide,


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Clouds form in the Martian at-mosphere much a s they do o n Earth,and the types of clouds seen aresimilar. However, all the clouds onEarth are made up of water or water-ice. As discussed previously, theclouds that form above the polar capsare made of carbon dioxide. Theclouds seen on volcano slopes (as early

morning fog in deep valleys) and in

storm fronts (like these cyclonicstorms) are made up of water or water-ice, as indicated by measurementstaken by the Infrared Thermal Mapper(IRTM) and the Mars AtmosphericWater Detector (MAWD) instrumentson the orbiter. These cyclones andother frontal storms were detected onthe surface by pressure indicators on

Lander 2 and were noted to pass byevery 3 to 4 days during the late falland winter. Cyclones occur when the

Figure 26

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cold polar air flows under warmer air ata lower latitude.

The storm shown at left isapproximately 250 km (155 miles)across while the storm shown below isabout 600 km (375 miles) across. Anestimate made from the cloud shadowsof the storm below indicates that it is 6to 7 km (4 miles) above the surface.

Figure 27

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As more and more dust entersthe atmosphere, the dusty atmosphereheats up more rapidly during the day,resulting in increased temperature dif-ferences between night and day in theupper atmosphere. Such differencescause large winds that pick up moredust so that the storms feed on them-selves and spread rapidly over the

planet. Prior to Viking each dust storm

season was thought to be much thesame; however, last Mars year thestorm was so mild it did not reachglobal scale. The previous year, justafter Viking's arrival, was marked bytwo full-scale global storms.

Here the southern hemisphereis completely engulfed in a north-spreading storm. Toward the top of th e

picture, the canyons are just visible at

th e edge of t he storm. It is thought thata global-scale storm cuts itself offwhen so much dust is in the at-mosphere that the sunlight is filteredout and peak temperatures at the sur-face fall. The winds then drop and thedust settles out. It takes about 3months for the atmosphere t o becomeclear again.

Figure 29


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Figure 30


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Two rregularly sha ped moons,Phobos and Deimos, orbit Mars. Thepicture to t he left is of Phobos , which is24 km (15 miles) across and circlesMars every 7.6 hours at an altitude of6000 km (3700 miles). Deimos, in thepicture below, is 12 km (7.5 miles)across and circles the planet every 1.3days at an altitude of 24 000 km(1 5 000 miles). Somewhat surprisingly,the two satellites look very different.Phobos has crisp craters and is crossedby numerous fractures which are barelyvisible in this picture. Demios appearsmuch smoother and t he craters have asofter appearance. The cause of thedifference is not known.

Figure 31

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The Viking SpacecraftOn July 20, 1976 , the first Vik-

ing spacecraft landed on the Martiansurface, followed by a second onSeptember 3, 1976. Almost 4 yearslater, the two landers are stilloperating, as is one of th e orbiters. Asecond orbiter was powered down onJuly 25, 1978, after it ran out ofattitude control gas. For almost 2 Mar-tian years the landers have been ob-serving changes at the landing sites

and making meteorological measure-ments. Meanwhile the orbiters havebeen systematically photographing th esurface and watching seasonalchanges in the atmosphere.

The entire surface has beenphotographed at a resolution of 200meters (625 ft) and a significant frac-tion at resolutions ranging down to 8meters (26 ft). Changing meteorologi-cal conditions were observed over theentire planet during this period, in-cluding the waxing and waning of

global dust storms. Changes at thepolar caps were also observed as theseasonal carbon dioxide formed anddissipated, leaving behind a remnantsummer ca p that is mostly water-ice inth e north and carbon dioxide ice in thesouth. Finally the orbiters made closeencounters with the two Martianmoons, at o ne point passing within 3 0km of Deimos and obtaining thehighest-resolution pictures ever takenof another object from an orbiter orflyby spacecraft.


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VIKING ORBITER 1 CHRONOLOGY

Date

J une 19, 1976J une 21, 1976July 9, 1976July 14, 1976July 20, 1976Aug. 3, 1976Sept. 3, 1976Sept. 11, 1976Sept. 20, 1976Sept. 24, 1976Nov. 25, 1976Jan . 22, 1977Feb. 4, 1977Feb. 12, 1977March 1 1, 1977March 24, 1977May 15, 1977July 1, 1977Dec. 2, 1978May 19, 1978July 20, 1979

Date

Aug. 7, 1976Aug. 9, 1976

Aug. 14, 1976Aug. 25, 1976Aug. 27, 1976Sept. 3, 1976Sept. 30, 1976Nov. 25, 1976Dec. 20, 1976March 2, 1977April 18, 1977Sept. 25, 1977Oct. 9, 1977Oct. 23, 1977July 25, 1978

Revolution

02

1924304375829296

15621322723526327833 1379898

10611120

Revolution

02

616182551

101123189235404418432

706

Event

Mars orbit insertionTrim to planned site-certification orbitOrbit trim t o mo ve westwardSynchronous orbit over landing siteVL-1 landing a t 1 153:06 UTCMinor orbit trim to maintain synchronization overVL-1VL-2 landingDecrea se of orbit period to be gin eastward walkOrbit trim to permit synchronization overVL-2Synchronous orbit overVL-2Solar conjunctionPeriod change to approach PhobosOrbit synchronization with Phobos periodPrecise correction to Phobo s synchronizationReduction of periapsis to300 kmAdjustment of orbit period to23.5 hoursSmall Phobos-avoidance m aneuverAdjustment of orbit period to24.0 hoursAdjustment of orbit period to24.85 hours; beginning slow walk arou nd planetAdjustment of orbit period to25.0 hours; accelera tion of walk rateRaising of periapsis to357 km; adjustment of orbit period to24.8 hours; a nd slowingofwalk rate.

VIKING ORBITER 2 CHRONOLOGY

Event

Mars orbit insertionPeriod and altitude adjustment; begin westward walk

Increase of period t o increas e walk rateDecrease of walk rate to proceed to landing siteSynchronous orbit over landing siteVL-2 landing a t 2237:50 UTCChange of orbit plane to75" inclination an d beginning of w estward walkSolar conjunctionLowering of periapsis to800 km and increasing of inclination to80"Synchronous over VL-2Period change: 13 revolutions equals 12 Mars daysChange of orbit period t o approach DeimosOrbit synchronization with DeimosChange of orbit period to24.0 hours a nd low ering of periapsis to300 kmPower down


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Figure Neg number

Figure 1Figure 2Figure 3Figure 4Figure 5Figure 6Figure 7Figure 8Figure 9Figure 10Figure 11Figure 12Figure 13Figure 14Figure 15Figure 16Figure 17Figure 18Figure 19Figure 20Figure 21Figure 22

'Figure 23Figure 24Figure 25Figure 26Figure 27Figure 28Figure 29Figure 30Figure 31

646A28731A41146S23627A28Mosaic664A5654 1 A20Mosaic466A54Mosaic737A65743A 1 5673A 12673830575B607281964693A38763A16184SllMosaic56B86383B49PanoramaPanoramaPanorama738A27783144221 1B24MosaicMosaic413B83

Cover: This painting by Gordon Leggof Graphic Films, Inc., Hollywood,Calif., was done for a NASA film ofViking. The m ulti-ringed caldera ato pOlympus Mons rises above the cloudbank which obscures the lower two-thirds of the volcano. The painting is

based o n Viking images obtained July31, 1976, from Viking Orbiter 1.


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Images of Mars the Viking Extended Mission

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