The Mariner 6 and 7 Pictures of Mars

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THE MARINER 6 AND 7PICTURES OF MARS


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This color picture of Mars shows greater detail than any Earth-b ased photo-graphs could provide. It was made by combining three black-and-white framesthat w ere take n b y Mariner 7 through color filters.


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NASA SP-263

THE MARINER 6 AND 7PICTURES OF MARSBY

Stewart A. Collins

Prepared at Jet Propulsion LaboratoryPasadena, California

Srrentlfic an d T e r h ~ li c a l n f o r n ~ a t ~ o wffice 1971NATIONAL AERONAUTICS AND SPACE ADMINISTRATION


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For sale by the Superintendent of DocumentsU.S. Government Printin g Office, Washington, D.C. 20402Price $4.25 Stock Number 3300-0367Library of Congress Catalog Card No. 78-610670


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ForewordMars, the fourth planet, is a subject of romance and mystery in human

culture. Astronomers, over the past century, have revealed that thisclose neighbor of Earth is in many respects its twin among the satellitesof the Sun. Its transparent atmosphere permits observation of the sea-sonal variation of its surface markings that long ago gave rise to specu-lations that Mars also harbors life as does Earth. The meager informa-tion we have had about Mars has stimulated a whole literature ofimaginative conjecture about the planet, which engendered and sus-tained the wide public interest in the scientific exploration of Mars byastronomical observation and space flight.

Mars is the planet most accessible for study from Earth, and mostamenable for research by modern space-flight techniques. It also posesscientific questions most likely to better our understanding of our homeplanet's origin, evolution, and fundamental processes, and thus to pro-vide knowledge potentially as beneficial to human affairs as it is inter-esting in an absolute sense. For these reasons the study of Mars hasbeen ranked top priority by the scientific community, as for instancein the recommendations of the Space Science Board of the NationalAcademy of Sciences. The National Aeronautics and Space Adminis-tration early in its history embarked on a progressive series of missionsto enlarge our knowledge of Mars. The initial reconnaissance of Marswas carried out in 1964 by the Mariner IV spacecraft, which transmittedto Earth close-up television pictures of the lunarlike, cratered, moun-tainous surface, and reported on the condition of the planet's atmos-phere and space environment. Mariner VI and VII in 1969 extendedthis reconnaissance in both detail and diversity of observations. Theplanned succeeding phases of investigating Mars will continue withMariner Mars Orbiter missions, to be launched in 1971, whose task isto lay the groundwork for atmospheric entry and soft landers on thesurface by the Viking program in 1976. The present volume presentsthe results of the Mariner VI and VII missions, in a more finished formthat has been issued hitherto. Greatest interest attaches to the 200-oddtelevision images which the world first viewed in their crude form asthey were received on Earth. This book tells the story of the teamworkthat produced this splendid result, and provides to the reading publicthe fruits of a venture that well characterizes the age of space ex-ploration.

HENRY J . S M I T HDe puty Associate Administrator (Scie nce )O fi ce of S pace Science and ApplicationsNational Aeronautics and Space Administration


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PrefaceThis book presents a comprehensive set of the television pictures

taken of Mars by the Mariner 6 and 7 spacecraft. These pictures arethe final results from the ambitious and complex television experimentof the Mariner Mars 1969 Project, a project managed by the JetPropulsion Laboratory (JPL) of the California Insti tute of Technologyfor the National Aeronautics and Space Administration. To most fullyutilize this television data, NASA has sponsored extensive post-flybycomputer processing and analysis of these pictures.

The purpose of this book is to make available high-quality repro-ductions of the final, computer-processed pictures. The text servesonly to explain the genesis and unique characteristics of the pictures,to point out interesting features in them, and to provide some indica-tion of their significance in the history of Mars investigations.

Detailed analysis has been avoided in this volume. Such interpreta-tion is the subject of the special supplenlent "The Mariner 6 and 7Pictures of Mars" in the January 1971 issue of the Journal of Geo-physical Research, a supplement which presents the observations andconclusions of the Television Experiment Team under the leadershipof Dr. Robert B. Leighton. The television team has not participateddirectly in writing this book.

The Mariner pictures are not copyrighted and may be obtainedthrough the National Space Science Data Center, Goddard SpaceFlight Center, Greenbelt, Maryland 20771 .

The author is indebted to the JPL Image Processing Laboratory,which prepared all the hlariner pictures used in this book, and toJaines K. Campbell, who provided the trajectory and viewing data.The valuable assistance of Mary Frail Buehler, Patricia B. Conklin,Patricia Shutts, David Thiessen, and Jaines H. Wilson is gratefullyacknowledged. The administrative and scientific judgment of Dr. A.Bruce Whitehead has also been essential to the preparation of this vol-ume. Chapters 1, 3, and 4 are based in part on material prepared byClaude M. Michaux, who also made the drawings. Finally, Drs. RobertB. Leighton, Bruce C. Murray, and Robert P. Sharp, all of the Tele-vision Experiinent Team, and G. Edward Danielson, Television Experi-ment Representative, have been very helpful in reviewing portions ofthis manuscript, correcting inisstatements, and helping the authorclarify the expression of many ideas.December 1970JET PROPULSIONABORATORYCALIFORNIANSTITUTEF TECHNOLOGYPASADENA,ALIFOI~NIA Stewart A. Collins

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ContentsChapter 1

a ions . . . . . . . . . . . . . . . . . . . . . . . . . . . .revious Investig t' 1Chapter 2

. . . . . . . . . . . . . . . . . . .he Spacecraft and the Mission 6Chapter 3

. . . . . . . . . . . . . . . . . . . . . .he Far Encounter Pictures 24Chapter 4

. . . . . . . . . . . . . . . . . . . . .he Near Encounter Pictures 80Chapter 5

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ummary 147

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ibliography 148

Appendix. . . . . . . . . . . . .ar Encounter Photoreference Table 153

. . . . . . . . . . . .ear Encounter Photoreference Table 157. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ASA Mars Map 160


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CHAPTER 1Previous Investigations

For thousands of years, Mars has intrigued man, for it has stoodapart as an unusual heavenly body. The ancients identified it as a"star7' which wandered about the sky and periodically varied in bright-ness. The early Greeks recognized that Mars was a "neighbor" of theEarth and first called it a planet.

Modern Martian exploration began during the seventeenth centurywhen Francesco Fontana first studied Mars with a telescope, identi-fied its gibbous phase, and thus found that Mars shone by light re-flected from the Sun. Fontana also saw on Mars a marking which hebelieved to be permanent, probably the dark, triangular Syrtis Major.In 1659, Christian Huygens sketched this feature and, by timing itspassage across the Martian disk, concluded: ". . . . the rotation of Marsseems to take place like that of Earth in 24 of our hours." In 1672,Huygens and J. D. Cassini observed the white area known as theSouth Polar Cap. In the early eighteenth century, Giacomo Maraldinoted that the polar caps changed size with seasons and that thesmall summertime southern cap was slightly offset from the SouthPole, a fact not then known to be true of the Earth's polar caps. Hewas also the first to observe changes in the location and size of surfacemarkings and remarked that some of these changes might be due toclouds.

About 1780, Sir William Herschel, continuing the work of Mdraldi,sought to correlate the color and size changes of features with theMartian seasons. In doing so, he located the Martian spring in theplanet's solar orbit. Herschel concluded that the polar white areaswere ice caps, the dark areas were oceans, the light areas were conti-nents, and that Mars had an atmosphere "so that its inhabitantsprobably enjoy conditions analogous to ours in several respects." Thesestatements, from such a respected authority, influenced subsequentinvestigators for over one hundred years.

The nineteenth century brought a host of Martian map makers. Twoof these men, Wilhelm Beer and Johann von Madler, established a


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Martian longitude-latitude system much like that accepted today andmore accurately defined the Martian rotation period to be 24 hours,37 minutes, 23.7 seconds. Giovanni Schiaparelli, starting in 1878, pub-lished a series of maps identifying features with Latin names, most ofwhich are still in use today. His maps' greatest significance, however,was not the settlement of international naming feuds. Rather, his mapsshowed many dark lines-he called them "canali" (channels) -inter-connecting the dark areas in a strange-looking network. "Canali" wassoon mis-translated into "canals," and intelligent life on Mars was sud-denly an intriguing popular concept.

As the idea of Martian life took firm root in public thought, anotherastronomer, Asaph Hall, discovered two small moons of Mars andnamed them Phobos and Deirnos. Phobos was found to revolve aroundMars three times faster than the planet rotates and would, therefore,

T he ma ps of Giovan ni Schiaparelli were th e first to use Latin nome nclaturefor Martian features. T his map, draw n in 1888, was mad e from visual, not photo-graphic, observations. I t shows many features visible in the Mariner pictures andalso man y "canali" (channels), which later caused e xcitement about the possibilityof M artian life .


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appear to rise in the west and set in the east twice daily. Deimos, witha period slightly longer than the rotation of Mars, would rise in theeast and travel slowly across the sky before setting in the west threedays later.

In 1892, as astronomers began to study canals more carefully,William Pickering discovered a canal crossing the dark area of MareErythraeum. This finding refuted the theory, surviving from Herschelone hundred years earlier, that the dark areas were oceans.

A new explanation of the changing sizes and colors of the dark areaswas then proposed: that these were land areas covered with a vegeta-tion that flourished in the spring and dried in the autumn. This theoryremained popular through the 1950's.

As Martian exploration entered the twentieth century, Martian lifefound its most ardent defender, Percival Lowell. Enthusiastic overSchiaparelli's canali, Lowell devoted his life and a fully staffed obser-vatory to the study of Mars. The canals, he proposed, were constructedby intelligent Mars inhabitants seeking to survive on a dry and for-bidding planet. As the polar caps melted during their summer seasons,the canals carried the melt-water away to the drier equatorial regionsto irrigate the life-sustaining crops there. Canals sketched by Lowellwere thin, straight lines so precisely arranged as to require an intelli-gent origin. During the ensuing debate, E. M. Antoniadi announcedhe had identified canals as an alignment of spots or ragged edges, notstraight, continuous lines. While many of Lowell's canals disappearedfrom later maps, they were erased much more slowly from the mindsof observers and the public. By 1930, Mars had been fastidiouslymapped within the limitations of visual observation.

The improvement of photography at the turn of the century intro-duced a new capability with which astronomers could compare obser-vations made many years apart. Thus began a systematic study ofseasonal variations, like the "wave of darkening7'-a progressive dark-ening from pole to equator of the dark areas in the hemisphere of themelting polar cap, and daily variations, such as the reported appear-ance of blue, white, and yellow clouds.

This century also introduced the use of new analysis instruments,such as spectroscopes, thermocouples (infrared radiometers ) , polar-irneters, and photometers, to planetary study.


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Th is Earth-based photograph w astaken in 1956 by Dr. Robert B. Leightonat the Mount Wilson Observatory. Justappearing near th e western lim b is SyrtisMajor, and just disappearing at th e east-ern terminator is Cerberus. Borderingthe South Polar Cap is the light areaAusonia. North is at the top.

Using a spectrometer, G. P. Kuiper discovered carbon dioxide in theMartian atmosphere in 1947. Similar ground-based studies later dis-closed small amounts of water and carbon monoxide and indicatedthat the Martian atmospheric pressure might be as low as 10-15 milli-bars, roughly 1%of that on Earth. With a thermocouple it was deter-mined that the surface of Mars was very cold, with temperaturesabove freezing only during summer days in the tropical latitudes.Polarimeters, measuring polarization, and photometers, measuringbrightness, suggested the bright areas included finely divided materialcontaining at least some ferric iron.

In 1965, more than 350 years after Galileo sought the first close-upview of Mars, the Mariner 4 spacecraft flew close enough to the planetto make a number of new measurements and acquire 22 televisionpictures. Mariner 4 found an extremely thin (5-10 millibars) carbondioxide atmosphere and sent pictures revealing Mars to be extensivelycratered.


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Mariner 4 provided man's first close-upctures of Mars. Frame 4N1 show ed th e'ar t ian l imb and the area Phlegra.rame 4N11, taken farther south, pre-' n t e d a c r a t e r 17 5 k i l o m e t e r s i nameter.


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CHAPTER 2The Spacecraft and the Mission

Shortly after the successful Mariner 4 mission, NASA authorized theMariner Mars 1969 Project. Mariners 6 and 7, launched by the morepowerful Atlas-Centaur rocket, were to greatly increase and improvethe observations made by Mariiier 4 and by Earth-based investigators.Thus scientists and engineers began to design a more ambitious ex-ploratory mission and to build larger, more sophisticated spacecraft tocomplete this mission.

The Mariner 1969 spacecraft we re larger (5.8 meters or 19 fee t) across the sola;panels and heavier (380 kilograms or 840 pounds) than any previous NASAplanetary spacecraft.


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This Atlas-Centaur, a massive vehicle of 145 metric tons, successfully launchedMariner 7 on March 27, 1969. Mariner 6 had been launched by a similar vehiclea m onth earlier, on F ebruary 24,19 69.

After more than 3 years of preparation, Mariner 6 was perched atopits Atlas-Centaur rocket 10 days before its scheduled launch towardMars. Unexpectedly, a faulty switch opened the main valves on theAtlas stage, and the rocket, as tall as a 12-story building, began tocollapse like a punctured tire. As the air roared out, two ground crew-men ran into the vehicle, started the pressurizing pumps, and thusprevented further "deflation" of the launch vehicle. While NASA pre-pared Exceptional Bravery Medals for these two crewmen, engineersbegan a thorough inspection of the complex Mariner 6 spacecraft anddetermined that it had sustained no damage during the mishap. Thespacecraft was removed from the wrinkled rocket and was placed


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upon another Atlas-Centaur. So successful was this switch thatMariner 6 was launched, on schedule, 10 days later toward its Marsencounter.

This ingenuity and flexibility of operation typified the entireMariner Mars 1969 Project. The two spacecraft, Mariners 6 and 7,incorporated two major improvements over previous planetary probes,improvements that encouraged adaptive operation. The first was theuse of programmable computers aboard the craft. In previous plane-tary missions, most of the sequences and other spacecraft instructionshad been read into the on-board computer prior to launch, and it wasdifficult or impossible to modify these instructions after launch. TheMariner 6 and 7 computers could be reprogrammed from the groundat any time during the mission. The second advance was the experi-mental high-rate telemetry system. This system, due in part to the new64-meter-diameter receiving antenna at Goldstone, California, enabled

Mariners 6 and 7 bo th followed a long solar orbit that carried t h e m graduallyout t o Mars. Mariner 7 was launched a ntonth later than Mariner 6 but arrivedonly 5 days later because of th e "inside track" ta ke n by Mariner 7. At the t imeof enco unter , Mars was 96 million kilometers (6 0 million miles) from Earth, andradio signals, traveling at th e speed of light, from th e spacecraft wer e receivedat Earth 5 minutes later.

\ \\ 96 m i l l i o n k i l o m e t e r s--,f -


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the Mariners to communicate 2000 times faster than Mariner 4. Thesetwo advances figured prominently in many after-launch decisionsaimed at increasing the quality or quantity of data or at correctingproblems that had arisen on the spacecraft.

The giant antenna, 64 meters (210 feet) in diameter, at the Deep Space Net-work's Goldsto ne, California, station toas an essential eleme nt of the h igh-ratetelemetry system. Other stations located around the world used antennas 26 me-ters (85 feet) in diameter.


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T h e science instrum ent scan platformwas mounted beneath the spacecraft, asshown in th e photograph. T h e platformwas movable so that the instrumentscould be pointed at different regions onMars. Un like previous Mariners, thesespacecraft carried no instruments togather interplanetary data during theEarth-Mars cruise. Th e entire missionwas focused on obtaining informatio nabout the Martian surface and atmo-sphere . Ins trum ents are : (a ) in fraredradiometer, ( b ) wide-angle television,(c ) ultraviolet spectrometer, ( d ) narrow-angle television, and ( e ) infrared spec-trometer.

Picture-taking activities for both Mariners were divided into twosequences: far encounter sequence and near encounter sequence. Tbefar encounter sequence took place during several days prior to flybywhen all of Mars appeared as a disk in the television pictures. Nearencounter included the 30 minutes during flyby when detailed pic-tures were taken of small areas on Mars. The pictures are identifiedby 'spacecraft, sequence, and picture number within that sequence.Thus 6F38 is the thirty-eighth picture taken by Mariner 6 during itsfar encounter, while 7N13 is the thirteenth Mariner 7 near encounterpicture. An abbreviated account of operations during encounter weekis given below.

Encounter EventsT u e s d a y , J u l y 29. Throughout Tuesday, Mariner 6 records 33 farencounter pictures on its tape recorder. The tape is played back and

the pictures are transmitted to Earth that evening. Originally, Mariner 6was to take only eight far encounter pictures, but the experimentalhigh-rate telemetry system has proved so successful that 50 such pic-tures will be returned by this spacecraft.


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Wednesday, July 30. Mariner 6 records an additional 16-1/5 pic-tures and transmits them back late in the afternoon. As flight con-trollers prepare for the complex Mariner 6 near ellcounter sequence, tooccur Wednesday night, contact is suddenly lost with Mariner 7. Mostpersonnel continue to prepare Mariner 6 while a smaller team concen-trates on solving the Mariner 7 problems. Both efforts climax at thesame time. While Mariner 6 begins recording its 25 near encounterpictures, a cheer goes up at the announcement that Mariner 7 com-munication has been re-established after a 7-hour silence. The dayends as Mariner 6 passes behind Mars.

Thursday, July 31. Spacecraft engineers analyze the data now beingreceived from Mariner 7 and determine that several problems stillexist. Post-encounter study will reveal that the Mariner 7 batteryprobably ruptured and vented its contents into the spacecraft. This inturn caused electrical transients that induced the spacecraft to spinlike a pinwheel and to lose contact with Earth. Now, however, themost serious consequence appears to be damage to the equipment thatreports the pointing direction of the television cameras. Since theMariner 7 cameras cannot be pointed properly without this informa-tion, work is begun t~ find a solution. On Thursday night, the25 Mariner 6 near encounter pictures, recorded a day earlier, areplayed back.

Friday, August 1. A scheme has been devised to calibrate the point-ing indicator for the Mariner 7 cameras. The cameras are turned onand begin transmitting pictures of black space. They are then movedaround in a search which climaxes when Mars appears in the cornerof one frame. Several additional corrections center Mars in the frameand provide the needed calibration. This operation, essential before anytelevision pictures can be acquired by Mariner 4, is possible because ofthe high-rate telemetry system which sends an entire picture in 42 sec-onds instead of the 35 minutes required by the standard system.

Saturday, August 2. Properly oriented once again, Mariner 7 records33 far encounter pictures and plays them back during the evening.

Sunday, August 3. Mariner 7 records and transmits an additional 33far encounter pictures. Analysis of the Mariner 6 data continues in aneffort to determine whether Mariner 7's plan should be altered in anyway to study interesting features seen by Mariner 6.


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Monday , August 4 . Mariner 7 records its final 25 far encounter pic-tures and plays them back. Mariner 7 now has taken a total of 91 farencounter pictures, quite a contrast to the eight originally planned.Mission planners have completed their study of Mariner 6 data andhave decided to assign to the still-limping Mariner 7 a more ambitiousjob than that performed by its sister craft. Far encounter data will besent back until one hour before near encounter-Mariner 6 stopped6 hours prior to encounter. Also, Mariner 7's near encounter coverageis increased to 33 pictures. This aggressive, last-minute plan is exe-cuted perfectly; and Mariner 7, following its sister's path, passesbehind Mars.

Tuesday ,August 5 . Mariner 7 plays back its 33 near encounter pic-tures, and both spacecraft continue in orbit around the Sun.

Postscript. At this writing 16 months later, both spacecraft areoperational and in regular radio contact with NASA's ground stations.As the spacecraft passed behind the Sun, the radio signal was used inthe most sensitive test yet made of Einstein's General Theory ofRelativity.

The Television SystemMariners 6 and 7 each carried two television cameras to photograph

Mars. At the near encounter distances from Mars, Camera A, with awide-angle lens, showed large areas of the planet (approximately1000 x 1000 kilometers, about the size of Alaska) and details as smallas 3 kilometers ( 2 miles). Camera B, using a telephoto lens, at thesame distance from Mars, showed smaller areas (100 x 100 kilome-ters, about the size of the Los Angeles basin) and details as small as300 meters (300 yards). The fields of view and shutter sequence wereplanned so that the A frames, taken sequentially through blue, green,and red filters, would overlap, and the B frames, taken through aminus-blue filter, would be located in the overlap area of two A frames.Most far encounter pictures were taken using the B camera.

A television picture taken by Mariners 6 and 7 is actually an arrayof points, each of which has a numerical value from zero to 255, rep-resenting the brightness at that point. Zero represents black, 255 indi-cates white, and the 254 intermediate numbers correspond to theintermediate shades of grey. Each picture is composed of 704 lines


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The two cameras carried by each spacecraft differed only in their opticalsystems. The wide-angle Camera A (t op ) used a 50-millimeter focal length Zeissplanar lens with blue, green, and red filters, while the high-resolution Camera B(bo ttom ) used a large (508-millimeter focal length) Cassegrain telepho to lens.

with 945 points, or pixels (picture elements) per line (665,280 pixelsper picture ) .

This numerical information was received in the telemetry from thespacecraft, stored on magnetic tape, and readily processed as numeri-cal data by computers. Through the use of a system roughly similar toa home television set, pictures were read off these tapes and werephotographed as they appeared on an electronic display screen.


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Shou;n here are the actualnumerical values of th e pointsi n a small portion of this pic-ture. In this large array ofnumbers, it is possible t o iden -tify a crater by the low datanum bers of its dark slopesand the high data numbersof the b right, sunlit slopes.


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This block diagram shows the television system in its near encounter modeand indicates the on-bo ard processing of the television signal.

CAMERAA

The Mariner 4 television experiment had shown Mars to have a verylow-contrast surface with only subtle detail. For this reason, duringnear encounter the electronic television signal was processed on thespacecraft into two forms of data: analog video and digital video.

The primary data form, the analog video, was processed (high-passfiltered) to emphasize small-scale details. This signal was nonlinearlyamplified to enhance high-frequency detail while sacrificing the fidelityof large-scale brightness variations. If such pictures had been taken ofEarth, small detail such as mountains, valleys, rivers, and coastlineswould have been enhanced, but differences between large deserts,oceans, and forests, for instance, would have been minimized.

The secondary data form, the digital video, was not enhanced andtherefore accurately preserved the large light-to-dark variations. Digi-tal video, however, was taken for only selected picture elements andrequired extensive computer processing before it could be used. In thefar encounter sequence, there was only one data type, a form of analogvideo to which the enhancement technique had not been applied andwhich therefore more accurately represented the actual scene.

-

Obtaining and transmitting the pictures to Earth was only half thejob. Remaining was the task of computer processing the pictures sothat they most accurately represented Mars. Eventually two versionsof pictures were produced-a maximum-definition version using onlythe analog video and a photometric version combining the analog anddigital video. The maximum-definition pictures showed maximum finesurface detail and the photometric version portrayed Mars as it actu-ally appeared, revealing fewer details but better showing the large-scalevariations.

AUTOMATICGA I N

CONTROLANALOG

TAPERECORDER

--CAMERA

CUBINGCIRCUIT

4P_,B

RADIO- TAPERECORDERLIPPERAMPLER DIGITALBIT- -


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Finally, several effects had beell introduced into the pictures by thetelevision system and had to be removed by the Jet Propulsion Labora-tory's Image Processing Laboratory, the computer facility designed forand devoted to processing television data. The primary unwanted fea-ture of the pictures was the coherent, or periodic, noise, whichappears as a basket weave pattern overlying the picture. Through theuse of computers it was possible to extract this and other patterns.A second uninvited feature in the pictures was the residual image

of previous pictures. Because vidicon television tubes do not entirelyerase the previous picture before they record the next scene, a faintimage of the previous picture can be seen in most pictures. This effectwas especially pronounced in limb pictures. Using computers, theimage processor removed this residual in the photometric pictures.Because of the effects of the enhancen~ent echnique used, such re-moval was impossible in the maximum-definition pictures in this vol-ume. Finally, the slightly nonrectangular shape of the pictures is dueto a geometric correction applied to them to compensate for opticaland electronic distortions.

Thus the pictures shown here are the final output from a long andcomplex sequence of operations both on the spacecraft and on Earth.

Opposite: A comparison between the maximum-definition and photometricversions of 6N13 is presented here. The top figure is a maximum-definition v er-sion, and th e bot tom slzows th e photometric version of the same picture, after th eanalog and digital data have been recombined. In the bottom figure, the darkeastern point of M eridiani S inus appears prominently as th e dark area in thecenter of th e picture, contrasting mitlz th e lighter desert to th e right. In th ema ximu m-de finition version, this light-dark contrast, wh ich actually appears onMars, has be en remov ed, and bo th areas are about t he same shade of gray. How -ever, in the max imum-definition version, craters are m uch more clearly visible inboth the light and dark regions.


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This sequence illustrates the way inwhich computer processing was able toremove c oherent noise from th e pictures.Notice the "basket weaue" pattern over-lying the picture information (top) . Th ecomputer analyzed such a picture andseparated the repeating pattern (center)from the random scene. This pattern wasth en subtracted from th e original pic-ture, leaving only the noise-free picture(bottom).


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ULTRAVIOLET WAVELENGTHSDETECTED BY SENSORS7 DIFFRACTIO N MIRROR

ULTRAVIOLET LIGHTEMITTED BY GASESIN MARS UPPERATMOSPHERE

FOC USIN G MIRROR!!The Mariner 1969 ultraviolet spectrometer was designed to study the upper

atmosphere of Mars.

Other Scientific ExperimentsIn addition to the television investigations, Mariners 6 and 7 per-

formed several other experiments designed to improve our understand-ing of Mars and the solar system.

Ultraviolet SpectrometerAtoms, ions, and simple molecules of hydrogen, oxygen, nitrogen,and such compounds as carbon monoxide and cyanogen were soughtin the upper atmospheres of Mars by the dual-channel ultravioletspectrometer. Prototype Mariner instruments were flown aboardsounding rockets before the Mars launch, providing comparison spec-tral surveys of Earth's atmosphere. One channel covered the range of1050-1900 11 and the other covered the 1900-4350 A spectrum.

The ultraviolet spectrometer experiment found no ozone in theatmosphere of Mars and indicated that solar ultraviolet light wasreaching the highly reflective South Polar Cap virtually unimpededby the atmosphere. Nitrogen, the major constituent of Earth's atrno-sphere, was conspicuously absent. Hydrogen and oxygen, both ionizedand neutral, were detected in small quantities, possibly the result ofthe breakup of water vapor and carbon dioxide by solar energy.


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Infrared SpectrometerThe infrared spectrometer was designed to detect a wide variety of

possible atmospheric species, including oxides and other compoundsof hydrogen, carbon, nitrogen, and sulfur. In addition the instrumentprovided a measure of surface temperature and offered the possibilityof obtaining reflection spectra identifying surface constituents.

The instrument used two semiconductor detectors, one cooled to165"K by radiation, the other to 22OK by a two-stage Joule-Thompsoncryostat using N, and H,. Rotating filters provided a spectral scanfrom 1.9 to 6.0 microns on the first channel and from 4.0 to 14.3mi-crons on the cryogenic channel. Most of the chemical species soughtwere not present at the detection limit; however, clouds of solid car-bon dioxide and of water ice were observed, and solid carbon dioxidewas detected in the vicinity of the South Polar Cap. In addition,reflection spectra indicative of silica or silicates were detected abovethe limb, suggesting either dust clouds or finely divided surfacematerial. Surface topography could be inferred from varying carbondioxide abundance (corresponding to the height of the atmosphere).Infrared Radiometer

The infrared radiometer measured the surface temperature alongthe path viewed by the television cameras. It consisted of an optical

This spectrum of the SouthPolar Cap, obtained by theinfrared spectrometer, con-tains features (labeled X andY ) ndicating solid carbon di-oxide is present either on thecap or in the atmosphereabove the cap.

WAVELENGTH, microns


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SPACE N IG HT SPACE

HELLAS

\POLAR CAP

Since the infrared radiometer was aligned parallel to the television cameras,this infrared temperature data acquired by Mariner 7 shows the temperatureat the centers of televis ion pictures an d along lines connecting these cen ters.Notice the temperature of the Polar C ap , approximately as cold as frozen carbondioxide wo uld b e at the prevailing Martian conditions.

system with dual thermopile detectors which sensed the thermal radia-tion in the 8- to 12-micron and 18- to 25-micron bands from a tinyregion along the track of the centers of the television pictures.

Temperatures as warm as the 280-290K range were observed inthe equatorial latitudes, and a value approximating the frost point ofcarbon dioxide at prevailing conditions was reached near the SouthPole. Few thermal anomalies were observed; generally the sunlit darkregions were warmer than corresponding bright deserts, and the tem-perature declined as expected as the field of view approached andcrossed the evening terminator. The darkest classical feature on Mars,Syrtis Major, was observed beyond the terminator and appeared stillto be warmer than the surrounding terrain.S-Band Occultation

Four times during the Mariner Mars 1969 encounters, the radio signalbetween the spacecraft and Earth passed through the atmosphere ofMars. Each spacecraft trajectory was designed so that the Marinerpassed behind Mars as seen from Earth, permitting the occultationanalysis at four widely separated points above Mars. The coherentradio signal was bent and retarded by the intervening atmosphere, and


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the physical properties of the air were investigated. The four locationsand the planetary radius and atmospheric pressure and temperature atthe surface are given below:

Radius, Pressure, Temperature,Location kilometers millibars O FMeridiani Sinus,4"N, 4"W 3393 6.6 37North Polar, 7g0N,276"W 3373 6.4 - 72Hellespontus,58"S, 330"W 3383 3.8 - 79Amazonis, 38"N, 148"W 3378 7.0 - 99

Celestial MechanicsThe accuracy with which the Mariner spacecraft were tracked per-

mitted investigators to infer the masses, positions, and motions ofthose celestial bodies whose gravitational fields influence the space-craft. These include the Sun, the Earth and Moon, Mars, and to alesser extent, Jupiter and other planets. Data obtained from Mariner 6and 7 confirmed calculations based on previous flights.


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FAR ENCOUNTER PICTURES


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CHAPTER 3The Far Encounter Pictures

Earth-based investigators were unable to photograph details smallerthan about 100 kilometers (62 miles) on Mars. The Mariner 4 tele-vision experiment, therefore, was a significant advance, for it showeddetail as small as about 3 kilometers. However, the area covered by anentire Mariner 4 picture was comparable to the smallest "point" seenfrom Earth, and thus it was not possible to confidently relate the"microscopic" Mariner 4 views to the telescopic Earth-based views. Tocompensate for this resolution disparity, Mariners 6 and 7 took a farencounter sequence of pictures showing the entire Martian disk atmuch higher resolution than was possible from Earth. These far en-counter pictures permitted more reliable interpretation of the laternear encounter pictures. Moreover, since the near encounter picturesshow only about 20% of the Martian surface, the far encounter pic-tures, providing coverage of almost the entire planet, contain muchdata that is independently interesting.


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Two days before its closest encounter with Mars, Mariner 6 begantaking telephoto pictures of the approaching planet. Mariner 7, start-ing 4 days later, took such pictures during 3 days prior to encounter.Both spacecraft approached Mars from slightly south of the equator,so that the South Pole was always tilted about 5 deg toward the cam-era and the North Pole was out of view just over the northern horizon.

As Mars rotated, features emerged from the western morning termi-nator, moved to the right (north is at the top) across the planet's disk,and disappeared behind the eastern late afternoon limb. Because thesun was not directly behind the spacecraft, a portion of the disk wasnot illuminated. It should be remembered, also, that the automaticgain control, described in Chapter 2, was not used during far encoun-ter, and thus the pictures closely represent the actual appearanceof Mars.

During th e 3 day s of Mariner 7's far enco unter , the spacecraft's distance fromMars chang ed from approxima tely 1,840,000 t o 130,000 kilom eters , causing a corre-spon ding increase in the apparent size of Mars.


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NORTH POLAR HO ODMARGARITIFER SINUS

MARE AClDAtlUMJWENTAE FONSTRACTUS ALBUS MERIDIAN1 SlNUSTITHONIUS LACUS AURORAE SINUS

MARE ERYTHRAEUM

AONIUS SINUS SOUTH POLAR CAP

NORTH POLAR HOOD MARE AClDALlUM

TITHON IUS LACUSNI X OLYMPICAAMAZONIS

)PRATES

PHAETHONTIS SOUTH POLAR CAP

7F0, the last picture taken to calibrate the camera pointing direc-tion, is interesting because it was one of the few taken of this areaof Mars. Normally during this segment of Mars' rotation, the taperecorders were being played back to Earth and thus no pictures wereacquired.

In 7F0, the dark features in the center are Aurorae Sinus andMargaritifer Sinus (see sketch simulating 7FO). Protruding from theeastern limb is Meridiani Sinus, and just emerging from the westernterminator is the Earth-observed "canal," Coprates. Frame 7F1, takenalmost 5 hours later, shows that Coprates has rotated to the extremeeastern side of the disk (see sketch simulating 7F1). Also visible, justsouthwest of Coprates, is the prominent dark feature Solis Lacus.Across the center of the disk stretches the desert Amazonis, whosemottled and streaked appearance suggests that greater detail is presentthan can be seen in this very early view. The dark area betweenAmazonis and the South Polar Cap is Mare Sirenum and Aonius Sinus.


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NORTH P OU R H O O D 7

PROPONTIS-ELYSIUM

CERBERUSAMAZONIS

/--NIX OLYMPICA

. -./. C.. -- .. -4 .. "W " CLOUD-.....-- --------MARE ClMM ERlU M MARE SIRENUMPHAETHONTIS

SOUTH PO UR CAP

From these far encounter pictures, it has been determined that theSouth Polar Cap extended northward to about 60 degrees south lati-tude. This is within a degree of the seasonal location predicted byastronomers and illustrates the regularity with which the cap advancesand recedes. Just visible near the terminator in 7F9 are two small darkspots: Cerberus and Propontis (see sketch simulating 7F9). Thesefeatures border the eastern part of the desert Elysium. Also, near thelimb of 7F9, there is a bright area which becomes brighter in the laterafternoon pictures, 7F10-11, climaxing as a very bright spot right atthe limb in 7F12 and 7F13. This afternoon brightening correlates withEarth observations of this region but remains unexplained. Release ofwater vapor from the soil is an interesting possibility.


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NORTH POLAR HOOD

NODUS LAOCOONTIS

MARE TYRRHENUM MARE ClMMERlUM

SOUTH POLAR CAP

As Cerberus and Propontis continue across the disk, the Polar Capbegins to show ragged detail along its northern edge, as in 7F15.Similarly: in 7F16, it becomes evident that the boundary between thedark Mare Cimmerium and the light Aeolis is ragged and broken, notsmooth and regular. Also, light and dark variations become prominentnear the North Pole (see sketch simulating 7F17).


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NORTH POLAR HOOD-

TRIVIUM CHARONTIS

MARE TYRRHENUMMARE ClMMERlUM

SOUTH POLAR CAP

Syrtis Major, a large, dark, triangular-shaped feature, appears in themorning sunlight in 7F23.Midway between Syrtis Major and Cerberusis the dark spot Nodus Laocoontis. Also more apparent in these pic-tures is the bright "hood around the North Pole. This hood appearsto consist of a haze which had formed over the north polar region atthe time of encounter.


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NORTH POLAR HOOD-7

NODUS LAOCOONTISSYRTIS MAJOR

MARE TYRRHENUM

MARE SERPENTIS

SOUTH POLAR CAP

The circular desert Hellas is very apparent south of Syrtis Major andjust north of the South Polar Cap (see sketch simulating 7F25).Hellas, like the regions in Amazonis, brightens as it approaches thelimb. However, unlike the Amazonis features, Hellas is plainly visiblefrom the early morning terminator throughout the day.


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NORTH POLAR HOOD7SABAEUS SlNUS

SYRTlS MAJOR

MERlDlANl SlNUSDEUCALIONIS REGlO

SOUTH POLAR CAP

MARGARITIFER SlNUS

MARE AClDALlUMJWENTAE FONSTRACTUS ALBUS MERIDIAN1 SINUS

TlTHONlUS LACUS AURORAE SlNUSMARE ERYTHRAEUM

AONIUS SlNUS SOUTH POLAR CAP

Extending to the west of Syrtis Major is the long dark Sabaeus Sinus,culminating in the two-pronged Meridiani Sinus (see sketch simulat-ing 7F33). Meridiani Sinus marks the zero point of the Martian longi-tude system.

7F33 was the last picture to be recorded on the first Mariner 7 tapeload. During the next 6 hours, these 33 pictures were read from therecorder and transmitted to earth. Also, during this time Mars rotatedso that Meridiani Sinus was on the eastern limb when the next picture,7F35, was taken. Frame 7F35, showing much the same view of Marsas 7F0, now reveals greater detail. The northern boundary ofAurorae Sinus is seen to be ragged with several disconnected smallmarkings in the lighter area. Another dark spot, Oxia Palus, is nowvisible just north of the tip of Margaritifer Sinus. North of Coprates isan additional marking, Juventae Fons.


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NORTH POLAR HOOD r HRysEMARE AClDALlUM

MARGARITIFER SINUS

JWENTAE FONSTRACTUS ALBUS MERIDIAN1 SINUSTlTHONlUS LACUS AURORAE SINUS

MARE ERYTHRAEUMSOLIS LACUSAONIUS SINUS

This page begins the side-by-side comparison of similar Mariner 6and 7 far encounter pictures. For both spacecraft, these pictures weretaken between 48 and 24 hours prior to flyby. Each Mariner 6 picturewas taken 5 days before the corresponding Mariner 7 picture. Afterextensive analysis and computer correction, there remains a significantdifference between the appearance of pictures from the two space-craft, a difference that is still unexplained, but is probably due to thetelevision system, not to Mars.

These pictures show more clearly the irregularity of the South PolarCap edge and the dark Mare Acidalium, in the northern latitudes.


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NORTH POLAR H O O D 7MARE AClDALlUM

TlTHON lUS LACUSNIX OLYMPICA

AMAZONISPHOENlC lS LACUS COPRATES

SOLIS LACUS

MARE SIRENUM ,-.----* AONIUS SINUSPHAETHONTIS SOUTH POLAR CAP

As Solis Lacus and Coprates move towards the limb, it becomesevident that Amazonis, long thought to be an uninteresting area ofMars, exhibits a great deal of fine detail. Apparent in 7F44 is thecircular feature Nix Olyrnpica, which had been known from Earth asan area that often showed seasonal variations in brightness. Thereappears to be a very complex and interesting arrangement of lightfeatures on this face of Mars.


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NORTH POLAR HOOD-

TlTHON lUS LACUSNI X OLYMPICA

AMAZONISPHOENlC lS LACUS COPRATES

MARE SIRENUM AONIUS SINUSPHAETHONTIS SOUTH POLAR CAP

Both 6F8 and 7F47 show Cerberus and Propontis once again emerg-ing from nighttime. They also reveal the gradual brightening of thefeatures in Amazonis as these features nioved toward afternoon.


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NORTH POLAR HOOD---\

.-.:PROPONTIS ,=-

ELYSIUM ,.---,CERBERUS

AMAZONIS

MARE ClMMERlUM MARE SIRENUMPHAETHONTIS

SOUTH POLAR CAP

The brightening of the Amazonis features climaxes in 6Fl l and7F50, where several of the spots are seen right at the limb. The brightregion seen in 7F9 can now be identified as several smaller spots,Another bright region, Phaethontis, does not brighten appreciably asit moves toward the afternoon limb. Rather, like Hellas, it appears toremain fairly constant in brightness.


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NORTH POUR HOOD-

TRIVIUM CHARONTIS

NODUS LAOCOONTIS


PHAETHONTIS

SOUTH POLAR CAPpF17Careful conlparison of the Mariner 6 pictures with those from

hfariner 7 suggests that the Polar Cap edge had changed very little ifat all during the 5 days between observations. Comparing these pic-tures with those taken farther from the planet, e.g., 7F15, one noticesthat these pictures show much greater detail in the northern boundaryof Mare Cimmerium. Particularly prominent is the linear projectionCyclopia, pointing toward the circular Elysium. Also, the northernpolar "hood" is more clearly defined than in the earlier pictures.


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NORTH POLAR HOOD-

TRNIUM CHARONTIS

MARE TYRRHENUMMARE ClMMERlUMw OUTH POLAR CAP

In these pictures, Nodus Laocoontis is seen more clearly to be adiffuse dark region in Aethiopis. Also, there now appears to be a fairlydefinite western boundary or gap in the north polar "hood."


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NORTH POLAR HOOD-

NODUS LAOCOONTISSYRTlS MAJOR

MARE TYRRHENUM

MARE SERPENTIS

SOUTH POLAR CAP

The region between Syrtis Major and Nodus Laocoontis is now seenin greater detail and reveals a mottled appearance. Compare thesepictures with the Earth-based photograph in Chapter 1.


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NORTH POLAR H O O D 7

NODUS LAOCOONTISSYRTIS MAJOR

AERlAIAPYGIA MARE TYRRHENUM

/--.. ..MARE SERPENTIS

HELLAS AUSONIA

SOUTH POLAR CAP

At this distance, a small dark feature may be identified just west ofthe tip of Syrtis Major. The resolution of these pictures is substantiallybetter than that attainable from the best Earth-based observations.


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NORT H POLAR HO OD7

MERIDIAN1 SlN UDEUC ALION IS REG1

SOUTH POLAR CAP

The pictures from both spacecraft show a definite darkening overthe southern limb. This could be either a surface property or a hazethat had accumulated over the Polar Cap.


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NORTH POLAR HO OD7ISMENIUS LACUS

THYMIAMATAMARE AClDALlUM MERIDIAN1 SINUS

OXlA PALUS SYRTIS MAJORMARGARITIFER SINUS SABAEUS SINUSDEUCALlONlS REGlOMARE ERMHRAEUM

MARE SERPENTIS

SOUTH POLAR CAP

7F66 and 7F67 reveal clearly that the feature Edom, in the notchat the junction of Meridiani Sinus and Sabaeus Sinus, is actually anoval crater approximately 600 kilometers in diameter. Notice also thedefinite brightening of Syrtis Major as it approaches the limb. Thiseffect contrasts with the relatively constant brightness of another darkfeature, Solis Lacus, as can be seen in 7F4345.


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NOR TH POLAR HO OD -7

THYMIAMATAMARE AClDALlUM MERlDlANl SINUS

OXlA PALUSMARGARITIFER SINUS

SYRTIS MAJORSABAEUS SINUS

DEUCALlONlS REGlOMARE ERYTHRAEUMMARE SERPENTIS

NOACHISSOUTH POLAR CAP

NORTH POLAR HOOD7 rCHRYSEMARGARITIFER SINUS

MARE AClDALlUM OX lA PALUS

JWENTAE FONSTRACTUS ALBUS MERlDlANl SINUSTlTHONlUS MCUS AURORAE SINUS

MARE ERYTHRAEUM

AONIUS SINUS SOUTH POLAR CAP

The pictures on this page are arranged sequentially because theMariner 6 and 7 pictures of this region do not correspond. Frame 6F33was being recorded when the Mariner 6 tape recorder reached the endof its tape after the first day of far encounter, and 7F69 was the firstpicture to be taken by Mariner 7 during its third day of far encounter.The remaining far encounter pictures, starting with 71769, are printedat half the scale of the previous pictures.

These Mariner 6 pictures provide the best far encounter coverageobtained of the Margaritifer Sinus region and show very clearly OxiaPalus and the definite mottling north of Aurorae Sinus (see sketchsimulating 6F30). Frames 7F69 and 70 show this same Aurorae Sinusregion farther along toward the limb. Notice in these two pictures thethree dark north-south streaks in this mottled area. Notice also thatthe "canal" Coprates can now be identified as a sequence of separatedark features aligned roughly east-west.


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NORTH POLAR HOOD-MARE AClDALlUM

TlTHON lUS LACUS

PHO ENlClS LACUS COPRATESSOLIS LACUS

AONIUS SINUSSOUTH POLAR CAP

6F34 is the first picture taken during the final day of the Mariner 6far encounter. These views clearly show the abundant Amazonis detailpromised by the previous day's pictures (e.g., 7F42). Nix Olympica isseen as two bright concentric rings, possibly a very large crater; andother similar, circular features appear throughout the "scrambledarea northwest of Coprates. In addition, several bright linear "wisps"appear in these pictures near the North Pole. They too brightennoticeably as they move toward afternoon. It has been suggested thatthey are clouds, but their identical position after 5 days tends to refutethis possibility. Another interesting feature now visible is the dark areawith an "M" shape, Phoenicis Lacus.


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NORTH POLAR HOOD-MARE AClDAL lUM

TlTHON lUS LACUS

PHOEN lClS LACUS COPRATESSOLIS LACUS

MARE SIRENUM AON IUS SINUS

SOUTH POLAR CAP

As the Amazonis region moves toward the limb, many of the briglit"markings become less distinct while the northern wisps" continue tobrighten. The South Polar Cap edge now reveals a crater due south ofNix Olyrnpica in 6F36 and 7F75. Such apparent topographic detailsuggests that some of the ground underlying the snow is cratered,similar to other Martian areas.


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NORTH POLAR HOOD-

PROPONTIS: -...... --.-

ELYSIUM !Q, -:-.\ ' ..A- ..CERBERUS

AMAZONISI.....&.*...-"-,.,.-./ --"

MARE ClMMERlUM MARE SIRENUMPHAETHONTIS

SOUTH POLAR CAP

As Cerberus emerges from night and assumes a distinctive "fish7'shape, parts of Amazonis, which were not identifiable at the center ofthe disk, become brilliant spots near the limb. Frame 7F79 is iiiterest-ing, for it shows the larger of the two Martian moons, Phobos, as asmall dot just east of Cerberus. From this and other pictures showingPhobos, its location has been defined more accurately than Earth-based data had permitted.


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NORTH POLAR HOOD

TRIVIUM CHARONTIS

NODUS LAOCOONTlS

MARE TYRRHENUM MARE ClMMERlUMa HAETHONTISIuOUTH POLAR CAPAs the spacecraft continues to approach Mars, the ragged northern

boundary of Mare Cimmerium becomes still more diffuse and ill-defined. In the Mariner 7 pictures, the dark mottled areas now beginto reveal numerous craters, and a distinct crater is now visible at thenorthern tip of Cyclopia. Frames 7F81 and 7F82 show an interesting"lump7' on the southeastern limb. Subsequent analysis has shownthis "lump" to be a detached haze layer in the atmosphere abovethe Martian surface. The Mariner 6 pictures show a bright area,Phaethontis, southeast of Mare Cimmeriuin.


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NORTH POLAR HOOD

NODUS LACXO


SOUTH POLAR CAP

Closer views continually reveal more craters in the dark areas. Also,in 7F83 there are two very bright spots in the northern half ofElysium. These pictures correspond roughly to the Earth-based viewin Chapter 1.


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N O R T H P OL AR H O O D7

N O D U S L A O C O O N T I S

AM RE TYF!RHENUMS A B A E U S S I N U S

M A R E S E R P E N T IS

S O U T H P O L A R C A P

A large crater (about 500 kilometers in diameter) appears inIapygia, near Sabaeus Sinus.


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NORTH POLAR HOOD7SABAEUS SINUS

SYRTlS MAJOR

MERlDIANl SINUSDEUCALlONlS REGlO

SOUTH POLAR CAP

These pictures show a multitude of craters in Syrtis Major. Like7F82, Frame 6F49 shows a definite layer of haze off the eastern limb.From a study of the far encounter limb data, it has been determinedthat there are definite haze layers in the Martian atmosphere but thatthese layers are not uniformly distributed over the whole planet.


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Playback of the final 25 Mariner 7 far encounter pictures was com-pleted about 3 hours before the spacecraft was to fly by Mars. Duringthe remaining time, the cameras were once again turned toward Marsto acquire the closest far encounter pictures of the mission (down to42,000 kilometers from the surface). These pictures were not recordedon the tape recorder, soon to be needed during near encounter; instead,the digital video form of these pictures was transmitted directly toEarth as the pictures were taken. In the digital video format, a column,known as the "jail bar," in the central area of the picture is blocked outand only every seventh pixel is transmitted for the remaining four-fifths of the picture. (Three of these pictures were combined to makethe color picture in the Frontispiece of this atlas.)

This close to the planet, it was possible to begin using the wide-angle Camera A with its four color filters: red, blue, and two greens.In these pictures, the blacked-out "jail bar" obscured the eastern por-tion of the planet. As observed froill Earth, the Martian surface showsgreatest contrast in red light and least in blue. Near the North Polein the blue picture there is a conspicuous bright feature which doesnot appear so prominently in the red and green. This evidence sug-gests that there was a blue-colored haze in the polar region at thetime of Mariner encounter.


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BLUE GREEN

RED GREEN

77


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This narrow-angle picture shows the southeast limb of the planet.Visible just beyond the limb is evidence of an atillospheric haze layer.


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NEAR ENCOUNTER PICTURES


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CHAPTERThe Near Encounter Pictures

The near encounter pictures are presented here in chronologicalorder. The total set of 57 pictures has been divided into five groups,each corresponding to a contiguous series of pictures taken while thecameras were pointed in a specific direction. The odd-numberedframes, e.g., 6N9, were taken with the wide-angle camera and arecalled "A" frames; the even-numbered pictures, taken with the narrow-angle camera, are called "B" frames. The five picture groups are:

6N1-8, Aurorae Sinus6N9-25, Meridiani Sinus7N1-9, Meridiani Sinus7NlO-20, South Polar Cap7N21-32, Noachis-Mellas

Opposite: Mariner 6 (t o p ) took pictures of the equatorial region of Mars;Mariner 7 (b ot to m ) flew b y farther so uth, taking pictures primarily of the south-erly latitudes and the South Polar C ap . Th e picture outlines have been super-imposed upon a globe made from Earth-based observations.


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Aurorae SinusAs Mars appeared in the television field-of-view, Mariner 6 began

to record pictures on its tape recorders. The first eight pictures, takenof the limb, Aurorae Sinus, and Pyrrhae Regio, revealed two significantfeatures: evidence of atmospheric haze at the limb and a previouslyunidentified, uncratered type of "chaotic" terrain. Far encounter pic-tures of this area, such as 7F69, showed several dark north-southstreaks and a very mottled texture. Although it is not positively iden-tifiabre, there appears to be a haze layer just beyond the limb in 6N1.This would corroborate the thin haze layers seen in some of the farencounter pictures.

High resolution frames 6N6, 8, and 14 show a jumbled, broken typeof terrain which has been labelled "chaotic." Careful study of boththe narrow- and wide-angle frames suggests that chaotic terrain coversa substantial portion of 6N5, 7, and 9, and that it does not clearlyresemble any areas on either the Earth or Moon. In the B frames thisterrain appears to be topographically depressed, lower than the sur-rounding cratered areas. Since there are few if any recognizable cra-ters in this chaotic area, it is inferred that chaotic terrain is youngerthan the surrounding cratered terrain and, perhaps, is presently devel-oping and expanding into cratered areas. (Frame 6N14, which for-tuitously overlapped this group of pictures, is discussed in theMeridiani Sinus group. )


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Enhanced photometric version


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6N1 (opposite), of the Martian limb over the Candor region, showsevidence of an atmospheric haze layer just beyond the limb. At bottomis an enhanced photometric version of 6Nl.

Beginning with 6N1, a photometric version of each wide-angle pic-ture will be included ( except for 6N23 and 6N25) . This version, whichhas been contrast-enhanced, provides an indication of the actual ap-pearance of Mars.

6N2 (above) is a highly foreshortened, high-resolution picture ofthe region very close to the limb.


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6N3 (opposite), including northern Aurorae Sinus, shows some ofthe dark streaks that were prominent in 7F69. The dark band downthe center of the picture is due to the residual image (an instrumentaldefect described in Chapter 2) of 6N1 and does not actually appearon the Martian surface. At bottom is an enhanced photometric versionof 6N3.6N4 (above) hints at topographic detail, but no features have yet

been positively identified.


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6N5 (opposite) provides a panorama of territory in which chaoticterrain has been located. At the moderate resolution of this wide-angleview, it is not possible to identify this terrain's small tell-tale detail-such identification depends on use of the narrow-angle frames locatedwithin these A frames. At bottom is an enhanced photometric versionof 6N5.

6N6 (above) is a narrow-angle frame that clearly shows the jum-bled, broken, and blocky terrain. There is a definite boundary, downthe center of this picture, between the chaotic terrain in the westernhalf and the smoother, cratered terrain to the east.


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6N7 (opposite) is the only A frame sharp enough to allow directdiscrimination between chaotic and cratered areas on the basis of topo-graphic texture. It also contains all three B frames, 6N6, 8, and 14,which show these boundaries at higher resolution. At bottom is anenhanced photometric version of 6N7.

6N8 (above) shows another example, in the lower right corner, ofa boundary between cratered and chaotic areas. Notice the fissuresapparently extending from this boundary into the cratered terrain.Such fissures add to evidence that chaotic terrain is probably youngerthan and encroaching upon the cratered terrain.


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6N9-25, Meridiani SinusAfter recording 6N8, the Mariner 6 computer "s lewed the television

cameras to point farther north and photograph the dark featureMeridiani Sinus. Later, after 6N13, a second slew directed the cam-eras southward again to s t ~ ~ d yhe boundary between the darkSabaeus Sinus and lighter Deucalionis Regio. In far encounter,Meridiani Sinus and Sabaeus Sinus appeared as very we11 defineddark features extending to the west of Syrtis Major (7F67, 6F30). In lo 0trying to identify such albedo variations in these near encounter pic-tures, it is important to remember the on-board processing explainedin Chapter 2, which served to minimize the visibility of such largealbedo variations. Careful comparison of light and dark areas has notyielded any sure explanation of the difference between them. Thetentative conclusion has been offered, however, that some light areasare areas of lower elevation onto which light dust has been trans-ported, possibly by winds.

These 17 pictures also offer the most extensive and comprehensivecoverage of Martian cratered terrain and thus lend themselves tocomparison with pictures of the Earth's moon. Such analysis has re-vealed that, unlike the Moon, Mars has two distinct crater classes:small, young, bowl-shaped craters and larger, older, flat-bottomedcraters, which have been strongly modified by unknown processes.


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E~lllaiiced hoto~netric ersion


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6N9 (opposite) is a somewhat oblique view of the western side ofMeridiani Sinus. There are perhaps some areas of chaotic terrain inthe lower left corner. At bottom is an enhanced photometric versionof 6N9.

6N10 (above) shows several of the small bowl-shaped craters thatare believed to be relative newcomers to the Martian landscape. Theiryouth is inferred from the lack of extensive erosion evident in thelarger craters. The two faint, dark annular features in the upper centerof 6N10 are defects of the Mariner 6 B camera, characteristic of allpictures taken with this camera; they are not markings on Mars.


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Enhanced photometr ic version


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6 N l l (opposite), another view of the Meridiani Sinus area, showsan abundance of the older, flat-bottomed craters. At bottom is an en-hanced photometric version of 6 N l l .

6 N l 2 (above) provides another high-resolution view of theMeridiani Sinus area.


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6N13 is the best Mariner 6 picture of Meridiani Sinus. An enhancedphotometric version, with the albedo variations apparent, is shown inChapter 2 and should be studied to better identify the large darkshape apparent earlier in far encounter pictures. This version, how-ever, shows clearly the very definite and intricate eastern boundary ofMeridiani Sinus. At the far right of the picture is the western portionof the large crater Edom, seen in far encounter, 7F67. Notice that thefloors of many craters within Meridiani Sinus appear to be coveredpartially with light material and partially with dark material. Thisobservation has led some geologists to surmise that a light-coloredmaterial, such as dust, has been transported from the light areas intothe depressed crater bottoms.


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6N14 is the first picture taken after the cameras were slewed backto the original track and tilted westward. This is a highly foreshort-ened view of chaotic terrain; and, fortuitously, this picture overlaps6N6, taken more than 4 minutes earlier. Notice the fissures whichappear to be expanding into cratered terrain from the depressed,chaotic "valley."


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Enhanced photonletric version


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6N15 (opposite) includes a portion of the limb in the upper leftcorner of this view looking back at Aurorae Sinus and Pyrrhae Regio.Notice the same diagonal features as those seen in 6N7. At bottom isan enhanced photometric version of 6N15.

6N16 (above) provides a ready conlparisoil between the two char-acteristic kinds of Martian craters. The large crater just right of centeris an example of a large (approximately %-kilometer diameter) flat-bottomed crater, with subdued edges and evidence of extensive modi-fication. On its rim is a small bowl-shaped crater with very sharpedges and a lip that appears to be slightly elevated above the sur-rounding ground.


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6N17 (opposite) shows another expanse of cratered terrain. At bot-ton1 is an enhanced photometric version of 6N17.

6N18 (above) contains in the lower left the edge of what is appar-ently a large, nearly obliterated "ghost" crater. While the prominentcrater in the upper middle of 6N18 may be easily identified in 6N14,this larger "ghost" crater edge is not apparent in the A frame.


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Enhanced photonletsic version


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6N19 (opposite) continues the panorama of Martian craters. Atbottom is an enhanced photometric version of 6N19.

6N20 (above) shows at the left a crater with a concentric double-ring appearance and, at the right, a ridge-like feature more than50 kilometers long.


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Enhailced photometric versioil


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6N21 (opposite) includes the boundary between dark Sabaeus Sinusand light Deucalionis Regio. Careful crater counts in both regions indi-cate there is no significant difference between crater distributions inlight and dark areas. At bottom is an enhanced photometric versionof 6N21.

6N22 (above), illuminated by a low Sun (14 degrees above thehorizon), reveals a surface with a great deal of subtle topography.


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6N23 (above) was taken at the afternoon terminator. Detail is lessapparent than in 6N21, an effect due perhaps to greater surface ob-scuration by an atmospheric haze or to the difference in filters throughwhich the pictures were taken.

6N24 (opposite, top), taken in very dim light, shows several pos-sible craters.

6N25 (opposite, bottom) was taken beyond the terminator.


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7N1-9, Meridiani SinusMariner 7 also obtained pictures of Meridiani Sinus during its nearencounter sequence. One of the most interesting aspects of these pic-

tures, however, is the information they have provided about possiblehaze layers in the Martian atmosphere. Meteorologic analysis of thisinformation has led to the following conclusion: Above this portionof the Martian surface there were probably three distinct, colorlesshaze layers located between 5 and 45 kilometers above the surface.


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7N1 (opposite) clearly presents the limb haze at the bottom of thepicture. At bottom is an enhanced photometric version of 7N1.

4N2 (above) was fortuitously taken of the limb. This high-resolutionview clearly shows the detachment of the haze layer from the surface.


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7N3 (opposite) shows the cratered terrain north of Meridiani Sinus.At bottom is an enhanced photo~netr ic ersion of 7N3.

7N4 (above) shows the fairly indistinct outline of several highlyforeshortened craters.


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7N5 (opposite) presents the dark mass of Meridiani Sinus. Again,reference to the photometric version is useful. Many of the cratersseen here are readily identified in the Mariner 6 near encounter pic-tures. Also, near the limb at the bottom of the picture is the easternportion of dark Oxia Palus (compare 7F35 and 6F33) . At bottom isan enhanced photometric version of 7N5.

7N6 (above) probably overlaps a small portion of the Mariner 6B frame, 6N12. Again notice the light appearance of part of many ofthe crater bottoms.


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7N7 (above) shows again the intricate detailof the eastern edge of Meridiani Sinus.

4N8 (opposite, top) provides a more detailedview of the craters south of Meridiani Sinus.The Sun is almost directly above this region, apossible explanation of the subdued appearanceof this topography.

7N9 (opposite, bottom) reveals more of thecrater Edom than was visible in 6N13. This pic-t.ure, taken through a blue filter, shows lowercontrast than 4N5 or 7, supporting Earth-basedobservations that the Martian surface exhibits 7N7reduced contrast in blue light.


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South PolarMariner 6 far encounter pictures had shown there was tantalizing

detail prominent both in the interior and along the edge of the SouthPolar Cap. This observation motivated the mission scientists and engi-neers to increase the Mariner 7 near encounter Polar Cap coveragefrom six pictures to ten pictures. After finishing their trace acrossMeridiani Sinus, the television cameras were slewed far south to thePolar Cap edge. These two mosaics provide the most graphic illustra-tion of the operation of the automatic gain control, described inChapter 2 . The top mosaic shows the Polar Cap as it would haveactually appeared to an observer aboard the spacecraft. The secondmosaic shows the maximum definition versions of these pictures. Inthis lower version, notice that the Polar Cap is about the same shadeof grey as the bare ground to the left and that a very dark band hasbeen artificially introduced along the cap edge. The attributes of thissecond version, however, are obvious when one compares the finedetail apparent both on and off the cap to the much less detailedrendition of these same areas in the upper mosaic.

The depth of snow inferred from these pictures and the low tem-peratures measured on the cap by the infrared radiometer have ledmost investigators to conclude that the snow is frozen carbon dioxide,"dry ice," not frozen water like the Earth's polar caps.


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7 N 1 0 (above) shows the area just north of the cap, and, because ofits bland appearance, is an enigmatic picture. Far encounter pictures,e.g., 6F40, suggested there was a haze over the morning portion ofthe Polar Cap; and such a haze, if present, could account for the lackof detail in 7N10.

7 N l l (opposite) provides a view of the Polar Cap edge. Topo-graphic detail is clearly seen through the snow layer. At bottom is anenhanced photon~etric ersion of 7N 11 .


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7N12 (above) is a deceptive telephoto view of the cap edge. Sincethe sunlight is coming from the left side of the frame, what appear tobe shadowed crater walls are, in fact, the sunlit slopes from which thesnow has been melted or sublimated by the direct sunlight. The brightslopes of the craters are the areas inclined away from the Sun wheresnow still remains.

7N13 (opposite) continues the picture track across the polar cap.For many craters, the rims appear brighter and the floors darker thanthe surrounding surface. In this area, crater shapes and distributionsare similar to those of nonpolar regions on Mars. At bottom is an en-hanced photometric version of 7N13.


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7N14 (above) presents some features apparently unlike any seenelsewhere on Mars. The large circular feature at the lower right, nick-named the "elephant's footprint," contains several very irregularly out-lined depressions that do not resemble craters. Here these features,referred to as "etch pits," appear to be quite shallow.

7N15 (opposite) shows more etch pits. In addition, there is a veryunusual, lumpy texture to the surface just below and to the left of thelarge, flat-bottomed crater near the right margin of the picture. Atbottom is an enhanced photometric version of 7N15.


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7N l 6 (above) introduces unusual features of seemingly positiverelief such as the bright, raised area near the picture center. Isolatedknobs and hills of this sort have not been identified elsewhere on Mars.

7N17 (opposite) includes the actual South Pole near the lower rightcorner of the picture. In the vicinity of the Pole there is a noticeablelack of craters and other features common elsewhere on the Polar Cap.Notice, also, the alignnlent of curved streaks around the Pole. At bot-tom is an enhanced photometric version of 7N14.


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7N 18 (above ) reveals the small-scale surfacetexture and features present deep within the Enhanced photometric version- -Polar Cap.

7N19 (opposite, top) displays a long, scal-loped arc which stretches about 900 kilometersacross the center of the picture and appears toseparate the heavily cratered Cap areas fromthe sparsely cratered central ones. The night-time ternlinator passes through the right side ofthis picture.

7N20 (opposite, bottom), the "giant's foot-print," is a feature straddling the scalloped arcseen in 7N19.


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After passing beyond the Polar Cap terminator, the cameras werepointed northward and back toward the limb again. The next elevenpictures showed additional cratered areas plus a new type of terrain,which has been described as featureless, in the floor of Hellas. Asseen in far encounter (e.g., 6F46), Hellas is a large circular area thatappears bright throughout its crossing from terminator to limb.


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Enhanced photo~netric ersion


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7N21 (opposite), our final view of the limb, looks north towardMeridiani Sinus, the dark area near the horizon. At bottom is an en-hanced photometric version of 7N21.

7N22 (above), highly foreshortened, shows some indistinct cratersand subtle linear markings.


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7N23 (opposite) includes much of Noachis. Craters seen here donot appear to differ significantly from those in Mariner 6 pictures. Atbottom is an enhanced photometric version of 7N23.

7N24 (above) reveals more flat-bottomed craters.


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7N25 (opposite) offers an interesting view of the transitional areabetween cratered terrain and Hellas. The diagonal ridges in the upperright corner characterize a gentle downward slope to the lower floorof Hellas, in the extreme corner. At bottom is an enhanced photomet-ric version of 7N25.

7N26 (above) is a high-resolution picture of these ridges and showsan otherwise largely smooth surface. Notice that the ridges appear topredate the craters in the lower left corner because the craters, likethose seen in 7N25, interrupt the ridges and are apparently not con-trolled by the ridges.


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7N27 (opposite) shows the distinctively featureless floor of Hellas.Three craters are visible near the western boundary, but none areclearly identified further into Hellas. Apparently, some process is oper-ating, or has operated, in Hellas which either prevents the formationof craters or erases such craters as they form. At bottom is an en-hanced photometric version of 7N27.

7N28 (above) is evidence of the lack of visible features at a resolu-tion of approximately 500 meters.


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7N29 (opposite) covers more of the Hellas floor. At bottom is anenhanced photometric version of 7N29.

7N30 (above) supports. the evidence of 7N28.


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7N31 (opposite) shows that even at the very low solar elevationangle of 8 degrees there are no identifiable features. At bottom is ailenhanced photometric version of 7N31.

7N32 (above), like 7N31, shows the lack of identifiable features onthe floor of Hellas.


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CHAPTER 5Summary

Since the seventeenth century, Mars has captivated man's imagina-tion. From rudimentary knowledge, man has imagined that Mars, ofall the planets, most closely resembles Earth and is perhaps capableof supporting life. Mariner 4 abruptly reversed these visions and sug-gested that perhaps Mars, heavily cratered and lacking Earth's denseatmosphere and strong magnetic field, more closely resembled theMoon. The Mariner 6 and 7 flights have finally revealed a uniqueMartian character, distinctly different from that of either the Earthor the Moon.

Martian crater shapes and size distributions differ significantly fromthe lunar counterparts. Chaotic terrain appears unlike anything recog-nized on either the Moon or the Earth; and featureless terrain has nolunar equivalent. Dramatic Polar Cap pictures reveal long ridges andirregular depressions of unknown nature and origin. Clearly, the handi-work of uniquely Martian phenomena is evidenced on the surface.

Tenuous, patchy layers of haze are seen in the atmosphere abovelocal regions of Mars. Mars' larger moon, Phobos, is found to be thedarkest object yet identified in the solar system.

Finally, Earthlings' views of Martian "life" have undergone majorevolution. Lowell's canal-constructing race can finally be abandoned.However, this does not eliminate the possibility that simpler microbiallife may have developed; nor does it diminish the importance of learn-ing whether life of any kind has ever existed or presently exists on theplanet. In this connection, Dr. Norman Horowitz has warned ". . . . itshould be noted that if Mars is to be a testing ground for our notionsabout the origin of life, we must avoid using these same notions to dis-prove in advance the possibility of life on the planet."

These 200 Mariner 6 and 7 pictures, taken in a brief span of 8 days,have told us much about our planetary neighbor and have raised manynew questions whose answers await the discoveries of future missions.


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BibliographyGlasstone, S., The Book of Mars, NASA-SP-179. National Aeronautics

and Space Administration, Washington, D.C., 1968.Leighton, R. B., et al., "Mariner 6 and 7 Television Pictures: Prelimi-

nary Analysis," Science, Vol. 166, No. 3901, pp. 49-67, October 3,1969.

Leighton, R. B., et al., "The Mariner 6 and 7 Pictures of Mars," SpecialSupplement, Journal of Geophysical Research, January 1971.

Mariner-Mars 1964, Final Project Report, NASA SP-139. NationalAeronautics and Space Administration, Washington, D.C., 1967.

Mariner-Mars 1969, A Preliminary Report, NASA SP-225. NationalAeronautics and Space Administration, Washington, D.C., 1969.

Slipher, E. C., The Photographic Story of Mars, Sky Publishing Cor-poration, Cambridge, Massachusetts, 1962.


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MARINER MARS 1969 TELEVISION EXPERIMENT TEAMROBERT. LEIGHTON,

Principal InvestigatorMERTON . DAVIESALANG. HERRIMANNORGAN . HOROWITZCONWAY. LEOVYBRUCE . MURRAYROBERT. SHARPBRADFORD. SMITHANDREW. YOUNG

California Institute of TechnologyRAND CorporationJet Propulsion LaboratoryCalifornia Institute of TechnologyUniversity of WashingtonCalifornia Institute of TechnologyCalifornia Institute of TechnologyNew Mexico State UniversityJet Propulsion Laboratory

MARINER MARS 1969 PROJECT MANAGEMENTN.W.CUNNINGHAM,ASAR. A. KENNEDY,ASAR. F. FELLOWS,ASAH. hl . SCHURMEIER,PLH. W. NORRIS,PLJ. R. CASANI,PLV. C. CLARKE,PLJ. A. STALLKAMP,PLM. S. JOHNSON,PLN. A. RENZETTI,PLW. R. DUNBAR,

Lewis Research Center

Program ManagerProgram EngineerProgram ScientistProject ManagerSpacecraft System ManagerDeputy Spacecraft System ManagerMission Analysis and Engineering ManagerProject ScientistMission Operations Systems ManagerTracking and Data System ManagerLaunch Vehicle System A4anager

MARINER MARS 1969 TELEVISION PERSONNELP. M. SALOMONS. B. SENGW. J. SLEIGHR. K. SLOANG. M. SMITHD. L. SMYTHL. M. SNYDERL. A. SODERBLOMJ. M. SOHAH. P. SQUYRESW. D. STROMBERGF. VESCELUS


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