the moon as viewed by lunar orbiter

8/8/2019 The Moon as Viewed by Lunar Orbiter

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N A S A SP-200

TH E M O O N A S V I E W E DBY L U N A R ORBITER

By L. J . KOSOFSKYnd FAROUKL-BAZ

Sci enf i f i c a n d T e c h n i c a l In f o r ma t i o n D i i i ~ i o t iOFFICE OF TECHNOLOGY UTILIZATION 1970L S R NATIONAL AERONAUTICS A N D S P A C E ADMINISTRATION

Washington, D.C.


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FO R SALE BY TH E SUPERINTENDENT OF DOCUMENTS, U S GOVERNMENT PRINTING OFFICEWASH INGTO N, D C 20402-PRICE 17 75-LI BRARYO FCONGR ESSCAT ALOG CARDNUMBER75-601482


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FOREWORDThroughout history men have wondered and dreamed aboutthe landscape of the distant Moon. Th e initial step in detailedknowledge of our nearest neighbor occurred with th e inventionof the telescope. A larger step came with the advent of th e spaceage. Automa ted spacecraft have provided u s photography ofvirtually the entire lu nar surface supplemented with other typesof da ta from a few discrete points. The se spacecraft have pavedth e way men ar e now following.A dedicated Go vernmen t-industry team placed five successfulLunar Orbiters into close orbits about the Moon in as manyattempts. Thousands of photographs were returned givingreality to the dreams of centuries. Some show area s smoothenough for initial manned landings; others reveal a fascinatingvariety of features for fut ure exploration missions. Some answerancient scientific questions; others raise new questions.This book contains a selected compilation of Lunar Orbiterphotographs that clearly illustrates the heterogeneous nature ofthe l unar surface. Many features shown are similar to thosefound on Ea rth ; others have no terrestrial counterpar t. Bycomparing the similarities and contrasting the differences, wecan hope to understand better our own planet and to recognizepossible implications for th e origin of the solar system. Increasedunderstandmg may profoundly affect our philosophic view ofourselves and our place in nature . The re may also be benefits

directly affecting our well-beina.The largest step of all in our search for answers is mannedexploration directly on th e lunar surface. Included in this bookare t he photographic guideposts that have been and a re beingused to plan t he most ambitious travels man has yet undertaken.I,. R. SchererDirector. Assistant Dire ctor ,Apollo Lunar Exploration,National Aeronautics andSpace Administration Space Administration

C. H. NelsonLangley Research Cen ter,National Aeronautics and

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CONTENTSChapter 1

IntroductionChapter 2

A Distant ViewChapter 3A Closeup View

MariaHighlandsCratersFaults, Rilles. an d DomesTh e Moon's Farside

appendixStereoscopic ViewsIndex MapsPhoto Reference Table

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39395262103124

138144150

V I 1


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CHAPTER 1

I N T R O D U C T I O N

T H E P R O G R A MTh e Lun ar Orbiter program was conceived, together with th eRanger and Surveyor programs, with th e primary objective ofproviding information essential for a successful ma nne d Apollolunar landing. Th e Lunar Orbiter program comprised fivemissions, all of whic h were successful. As th e primary objectivesfor the Apollo program were essentially accomplished oncompletion of th e th ird mission, the fourth a nd fifth missionswere devoted largely to broader, scientific objectives-photography of the entire lunar nearside during Mission IV andphotograph y of 36 areas of particular scientific interest on th enearside d uring Mission V. Photograph y of the farside during

th e five missions resulted in an accumulated coverage of morethan 99 percen t of th at hemisphere. Th e detail visible in th efarside coverage generally exceeds tha t previously attained byEarth-based photographs of th e nearside; in some areas objectsas small as 30 meters ar e detectable.Initiated in early 1964, th e Lunar Orbiter program includedth e design, development, and utilization ofa complex automa tedspacecraft technology to support the acquisition of detailedphotographs of the lunar surface from circumlunar orbit. Thefive spacecraft were launched at 3-month intervals betweenAugust 10, 1966, and August 1, 1967.In addition t o its photographic accomplishments, th e programprovided information on t he size and shape of th e Moon andth e major irregularities of its gravitational field. Th is seleno-detic information was derived from th e tracking data. Micro-meteoroid and radiatio n detectors, mounted on the spacecraftfor ope rationa l purposes, monitored those aspects of the luna renvironment.

PHOTOGRAPHIC ACCOMPLISHMENTSPhotog raphs for Apollo (MissionsI, 11, an d 111)

The primary objective of the Lunar Orbiter program was tolocate smooth, level areas on the Moon's nearside and to con-firm their suitability as m anned l anding sites for th e Apollo

program. To accomplish this, photographic coverageat a groundresolution of 1 meter was required of are as within 5" of theequator between longitudes 45" E an d 45" W-the zone ofprimary inter est to th e Apollo program.Twenty potential landing sites, selected on the basis of Ear thobservations, were photographed d uring thesitesearch missionsof Lunar Orbiters I an d 11. Lunar Orbiter I11 rephotographed12 of th e most promising of these ar eas dur ing its site-confirma-tion mission. Following analysis of these photographs, con-sideration was furthe r reduced to t he eight most promising areas.However, to make the final selection of th e candidate Apollolandin g sites, additional photo graphs of various ty pes wererequired a t all but three of these areas. Thes e photographs,obtained during Mission V, rovided sufficient dat a to permitth e final site selection an d mapping.Approximately three-fourths of the film supply of the firstthre e missions was used to photograph areas of interes t to th eApollo program primarily. The remainder could not be usedfor such are as because of operational film-h andling require-ments; i.e., th e film could not re main statio nary in the camerafor long periods of time lest it deterior ate. Photo graph s takenwhen th e areas of primary interest were not in view, referredto as film-set frames, were expended in a variety of ways andfor several reasons. In t he Mission I flight plan, s uch sites wereselected, in real time, for diagnostic tests of certain spacecraftmalfunctions, for reconnaissance of potential photo sites forsubsequ ent missions, an d for photog raph y of th e Moon's farside.T o minimize operational d emand s on Mission I. nearly all ofth e film-set exposures were made using conventional maneuversof th e spacecraft. Th is resulted in near-vertical photographsfor all but two are as covered during Mission I. Two obliquephotographs of the Moon's farside, with the E art h in th e back-ground, were taken while the spacecraft was passing behindth e Moon's eastern limb. Th e scene provided in these obliqueviews and the flawless execution by the spacecraft of everysingle maneuver command during Mission I prompted morerigorous performance demands for the following missions.Specific plans t o u se th e film-set frames were included in th epreflight design of Missions I1 an d 111. Several outstanding


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Nearside Farside

Lunar Orbiter I5_$. . . . : 1 1 1 ,@. . ., . Lunar Orbiter 1 1

/ I

V

Lunar Orbiter Il l

Lunar Orbiter I V

Figure I. Photographic Coverage , R E P R I N T E D R Y PERhI I SSl Oh FROM HE L M A RO R R I T E R U l S S l O N S T O THE M O O N BY L F V I N . V l E L E AND E L D R E N K u I P C O P Y R I G H T MA Y l P i 8 R YSCI ENTI FI C AhtERICAV. lN C .ALL R I G H T S RBSERYED 1

oblique photographs were obta ined on both t he nearside andthe farside. Th e Mission I1oblique view of t he cra ter CopernicusIS a notable example.Because the area of Apollo interest was near t he equator andI-meter resolution was required, photographs taken duringMissions I, 11, and 111 were made from low inclination, close-inorbits. Thi s restricted the north and south latitude range for

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photography and also the total area coverage obtained. Theserestrictions were relaxed for th e final two missions.Photog raphs of General Scientific In tere st (Missions JV and V )

T he flight plans for Missions I V an d V incorporated near-polar circumlunar orbits from which virtually any part of theMoon could be photograph ed. Mission I V photography, con-ducte d from high-altitude orbit, was a broad. systematic surveyof the enti re nearside. Most of this photograp hy contains detaildown to 60 meters ground resolution, and the remainder is nocoarser tha n 150 meters. Th e east and west limbs and bothpolar regions were covered in near-vertical views.T h e primary objective of Mission V was to obtain closeupphotographs of geologically interesti ng feature s in 36 selectedarea s of th e Moon's nearside. In ad dition, some photographswere taken t o complete the Apollo requireme nts and t o completethe coverage of the lunar farside. A ll of these objectives wereatta ined with th e faultless execution of Mission V, completingthe Lunar Orbiter program.Figure 1 summarizes the five missions, showing the orbit ofeach one an d t he a rea th at each covered photographically.

TYPICAL M I SSI ON PROFILEEach mission started with the launch from Cape Kennedy

by an Atlas-Agena D launch vehicle. Following separation fromth e Atlas, the Agena engine put th e spacecraft into E art h orbit.After a coasting period, a second burn of the Agena engine,before se parati ng from it, placed th e spacecraft on a translunarcourse. A small correction in th e traject ory was accomplishedby a sho rt burn of th e spacecraft's velocity-control enginesome20 to 30 hours after leaving Ea rt h orbit. Upon arriving at thelunar encounter point, after some 90 hours, the spacecraftvelocity was reduced by a retrofiring of its engine, leaving it inan elliptical posigrade lunar orbit. Inject ion into orbit wasscheduled in all cases within a few days of new Moon, and a norbit was established with pe rilune (poi nt of closest approa ch)near th e equator on th e Moon's eastern limb.After being tracked in this orbit for several days, the space-craft was slowed again, lowering th e orbital perilune t o thedesired photographic a ltitude. Th e perilune altitude was about46 kilometers on the first three missions, lo00 kilometers onMission IV, and 100 kilometers on Mission V.The placement of th e orbital plane had t o be such tha t, whenth e Moon's rotation brought t he selected sites benea th theperilune, th e si te would be properly illuminated for photography(Le., have the Sun 10" to 30" above the local horizon). Ingeneral, the sites on the Moon's nearside were photographedwith sunrise illumination an d the farside areas with sunsetillumination.

Th e picture-taking phase was completed about the time ofthe full Moon, and the entire photographic mission ended withthe readout and transmission of the last of the photographicdata in about 30 days. The spacecraft remained in orbit andwas tracked for extended periods to provide additional lunargravitational and o ther environmental data. Th e longest life-time in orbit was 335 days, for Lunar Orbiter 11. A ll thespacecraft except Lunar Orbit IV were deliberately crashedonto the Moon, by a final burn of the velocity-control engine,to ensure that they would not interfere with communicationbetween the Ea rth and later spacecraft. Communication withLunar Orbiter IV was lost after 70 days in orbit, about 3monthsbefore it is believed to have crashed.Lunar Orbiter Spacecraft

Figure 2 shows the Lunar Orbiter spacecraft in its flight con-figuration. It weighed approxima tely 390 kilograms (850 pounds)at launch. A t launch, the spacecraft rode within a n aerodynamicnose fairing atop the Atlas/Agena D launch vehicle, its solarpanels folded under the spacecraft base and antenn as heldagainst its sides. In this launch configuration the spacecraftwas approximately 1.5 meters (5 feet) in diameter and 2 metershigl:. After injection into the cislunar traje ctory, with t he solar


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panels and antenna s deployed, the maximum span became5.2meters along the an tenna booms and 3.8 meters across the solarpanels.Three-axis stabilization was provided using the Sun and thestar Canopus as primary references and a three-axis inertia lsystem for periods wh en th e spacecraft was required to opera teoff celestial references durin g maneuvers or when th e Su n andCanopu s were occulted by th e Moon. After assuming th ecommanded attitude for a picture-taking sequence, th e space-craft would maintain that attitude through the sequence.Attitu de control was mainta ined by cold-gas thrusters. A flightprogrammer w ith a 128-word memory provided the capab ilityfor up t o 16 hours of automatic spacecraft and camera operationor for action o n real-time commands.Photographic System

The complete Lunar Orbiter photographic system includedth e spacecrafts photographic subsystem: the ground recon-struction electronics (GRE):nd the communications system.

Rocke t enuine/Att i tude control jetsnropellant tank

eteoroid detectorDirect ionalantenna Flight

/ proqramrner/Canoms tracker

,/Omnidirectionalantenna

/ Solar panelPhotographic subsystemFigure 2. Lunar Orbi ter Spacecraft

The photographic subsystem recorded a negative image of lunarscenes on film that was developed and scanned to provideelectrical signals for transmission to the deep space stations(DSS). The video signals from the communications systemwere fed to the GR E which reconverted th ese signals int ophotographic images at a scale 7.18 times the spacecraft scale.The transmitted signals were also recorded on magnetic tape.A brief description of the Lunar Orbiter photographic systemfollows. For a more detailed description, the reader is directedto the group of five papers in the Journal of Society o f MotionPicture and Teleiiision Engineers, August 1967. pages 733-773.The Photographic Subsystem

The spacecrafts photographic subsystem. shown schemati-cally in figure 3. comp rised a dual ca mera, a film processing unit ,a readout scanner, and film-handling apparatus. The two cam-eras operated simultaneously. placing two discrete frame expo-sures on a common rollof 70-mm film. Each camera operated a t afixed f/5.6 lens aperture, at shutter speeds of either 1/25, 1/50,or 1/100 second. Th e high-resolution ( H ) frame was exposedthrou gh a 610-mm narrow-angle lens and a focal plane shutte r.The medium-resolution ( M ) frame was exposed through an80-mm wide-angle len s and a between-the-lens shutter .T h e film supply con sisted of 79 meters of unp erforated 70-mmKodak special high definition aerial film, type SO-243. Thisfine-grain film has a recording cap ability (450 lines/mm) well

above the photographic su bsystem requirements (approximately76 lines/mm) an d a low enou gh speed (ae rial index of approxi-mately 3.0) to make it relatively insensitive to space environm entradiation.The selection of a slow-speed film to meet t h e Apollo require-ments for 1- and &meter resolution photographs necessitatedthat image-motion compensation (IMC) be provided to minimizesmear. An electric-optical sensor viewed the lun ar surfacethrough a portion of the 610-mm lens and determined the ratioof th e spacecrafts velocity to its altitude-referred to as th evelocity-to-height (V/H) ratio. Th e V/H senso.. outpu t, in th eform of a mechanical camshaft rotation, was used for directdrive of the camera platens (and film) at the proper rate toensure IMC during exposure. T h e V/H sensor also controlledthe spacing of exposures dur ing multiple exposure sequences.Th e two camera axes were coincident, so tha t the coverageof th e H-frame was cente red with in the. M-frame coverage asshown in the upper left portion of figure 4. Because of thephysical a rrangement of th e two-lens system, adjace nt exposureswere recorded on the film in the interlaced manner shown inthe lower portion of th e figure, Exposure times were recordedin digital form on th e film alongside th e M-frames. Th e leastreading of time was 0.1 second.Th e upper right part of the figure shows a n enlarged portionof th e edge data preexposed on the film. Th e pattern includeda gray scale and resolution bars to permit late r calibration andevaluation of th e p hotographs, various markings for the controlof th e readout operation, and framelet numbe rs to facilitate th ereassembly of the frames on th e ground .The film-processing method was the Kodak Bimat diffusiontransfer technique. Th e film, on enteri ng th e processor, waslaminated wit h th e processing web, as indic ated in figure 3.A gelatin layer on the processing web was slightly damp , havingbeen soaked in th e monob ath processing solution before beingloaded into th e spacecraft. Th e monoba th solution developedth e exposed p ortions of th e SO-243 film to a negative imageand transferred the undeveloped silver ions to the processingweb, where they were reduced to form a positive image. (Th isis essentially the technique used wi th Polaroid Land black-and-white film.) As the process went to completion within 3%minutes of co ntact time, image quality wa s no t affected byprolonged contact. Coming off the processing drum, the twofilms were separated. T h e negative film went through the dry-ing section, and the processing web was wound on a takeupspool. ( N o use was made of t he positive images on th e web.)After being dried, the negative film went through the readoutscann er to its takeu p spool. During reado ut, th e film movedbackward through the scann er. Th e readout looper shownbetween th e processor an d th e scanne r made it possible to readout selected portions of the film before photography was com-pleted.Upon completion of photography, the processing web wascut and pulled free of t he processor. Th e negative film couldth en be read out completely (from th e last exposure to the first)an d be pulled through th e processor and camera onto the supplyspool.. Th e readout scanner (fig. 5) converted the photographicimages into electrical signals by scan ning th e negative film witha microscopic spot of high-intensity light. The source of thelight was the linescan tube shown at the upper left. This wasa special cathode-ray tube whose phosphor layer was coatedon a rotating cylindrical metal anode. Its outp ut was a brightspot of light th at repetitively traced a line across th e phospho rdrum.The scanner lens focused a 0.005-mm spot of light on th efilm. Th e electrical scan of th e spot traced a line 2.68-mm longon t he film in the direction parallel to the film edge.Th e mechanical scan of th e line across th e width of the filmwas accomplished by the slow back -and -forth movement of thescann er lens. One t.raverse of the scanne r lens required 22seconds, during which time the electrical scan was repeatedover 17,000 times. Before the s canne r lens started across th efilm in th e reverse direction, th e film was moved 2.54-mm in th ereadout M e . Th e resulting sections of spacecraft film scann ed

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in this manner, referred to as framelets. are the basic unitseventually used for the ground reassembly. Th e scanning of acomplete dual exposure took 43 minutes.The intensity of light reaching th e photomultiplier tube wasmodulated by the density of th e image on the film. Anelectrical signal proportional t o th e intensity of th e transmittedlight was generated, amplified, and fe d to the spacecraft com-munications subsystem.

TRANSMISSION AND RECONSTRUCTION OF PHOTO-GRAPHSThe video data coming from the photographic subsystemoccupied a frequency spectrum from 0 to 230 kilohertz. Thissignal was modulated on a 310-kHz subcarrier (single sideband,suppressed carrier). The video signal, telemetry signals, and a38.75-kHz pilot to ne were summed, and th e resulting compositesignal phase-modulated th e S-band (2295-MHz) carrier.A 10-watt traveling-wave tube amplifier and a 92-cm para-bolic antenna transmitted the signal to Earth, where it wasreceived at one of the three d eep space stations (DSS). Th e10-MHz intermediate frequency of th e DSS receiver, containingth e composite signal. was recorded on magnetic ta pe fo r perma-nent storage. At t he same time, it was passed to th e groundcommunications equipment which recovered th e telemetry andvideo.The video signal was fed to the ground reconstructionelectronics (GR E) where it was converted int o an intensitymodulated line on the face of a cathode-ray tube. In a con-tinu ous motion camera, 35-mm film was pulled past th e imageof this line, recording each readout framelet at 7.18 times th e

Film takeupand storage

Readout looper

Figure 3. Photographic Subsys tem

Figure 5. Readout Scanner

spacecrafts image size. T h e recording film was cut up int oframelets, which were th en reassembled into enlarged replicasof the original spacecraft frames. T h e M-frames were re-assembled in complete form, while the H-frames, which wouldbe about 1.5 meters long if fully reassembled, were reassembledinto th ree co mponent sections.

PATTERNS OF PHOTOGRAPHIC COVERAGEA single exposure of the dual-frame camera produced thenested ground coverage shown inthe upp er left portion of figure6 . (Th e ground dimensions are shown for a vertical cameraattitude and a flight altitude of 46 kilometers.) Th e groundcoverage could be expanded in the direction of flight bysequential exposures, an d in th e perpendicular direction byphotograp hing from successive orbits.

CAMERA FIELDS OF VIEWa

Direction 2.29 rnm

Time of expow

L H - f r a m e ~ ~ 3 m m 1 L M - f r a m e1610-mrn c a me r a l L 2 rnrn 1 (80-mm camera)

iTimel LTime 36FILM FORMAT

Figure 4 . Film F or mat4


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1. 4, 8.and 16 exposures. An rate could be selected. At either rate,exposures was automatica lly determinedof eight exposures a t the slow rate produced the6. The52 percen t, providing continuous stereo-over nearly the full length of the strip. Th e

5 percentrames thus providing high-resolution coveragep without gaps. Th e overlaps of th e M-frames at88 percent.6 shows the coverage patter neight-exposure sequences at th e fast rate,A small overlap between theof H-frames provided contiguous high-resolutionconsiderable area.the lower right was also produced by twoe fast rate. Here the camera was

angle of convergence between th e two orbitalfigure 6 were typical of th e first three

near their perilune. T he orbits of Missionsle th e spacecraft was going from sout h to north.are shown in figure 7.of figure 7 shows the typical ground coverage ofo successive orbits during Mission IV. This29 orbits to obtain complete cover-Note tha t for Mission IV only, thee H-frame is oriented approximately in theEa ch M-frame covered nearly all of th e lunarto t he spacecraft.

es of four exposures each duri ng Missionth e end of thi s book were all printed fromM-frame coverage of such sequences. A con-coverage pat tern (not shown) was also employed

P I CT U R ESth at have been cropped and enlarged or reduceded lu nar features at scales approp riate to thePhoto Reference Table in the Appendix suppliesas well as th e(for the medium resolution, or 80-mm focalor H (for th e high resolution, or 610-mm focalparallel lines, th at can be seen in each picture,f t he framelets introduced by th e read-

e pictures. Th ey provide the most convenient number of meters on the M o o n covered by oneTh ey also help in visualizing th e size rela-

26, and each H-frame 86, framelets.framelet lines provide a reference for the azimuth

e oriented with North approximatelyat the right, following the convention

adopted by the International Astronomical Union at Berkeleyin 1961. Oblique photographs may be oriente d in oth erdirections as they can only be viewed naturally when thehorizon is at the top. Others were rotated from th e normalorientation in order to fit selected features within the rectan-gular format of the book a t th e most favorable scale for viewing.These can easily be identified, as the framelet lines are no tparallel to th e picture edges. The se pictures include a smallarrow showing the North direction.The pictures whose framelet lines are parallel to the pictureedges do no t have the North direction precisely at th e top. T hecameras actually were oriented parallel to th e ground trac k oft he spacecraf t o n Missions I , 11, 111, an d V, in order to achieveimage - motion compensation, and the framelet lines also areparallel to t he ground track. (On Mission IV, where the orbita laltitude made image - motion compensation unnecessary, the

r\( 80 rnm p m e r a c ov er ag e52% forward overlap

16.6 km 7\Monorcopic coverage88% forward overlap

iguous coverageDirect ion of f l ight

onvergent stereo

Figure 6. Coclerage Pat/ems-Missions I . I I . and I I I

i

Figure 7. Coverage Patterns-Missions IV a n d V

Direct ion*yIf f l ight


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camera orientation was determined by righting considerations.)Th e framelet lines of these pictures are always within 22 ofthe Moons cardinal directions, and the captions do not havea No rth arr ow. In order to kn ow their orTWtBtioh more pre-cisely, the reader should refer to the Pho to Reference Table,which gives th e lunar bearing of the framelet lines.Th e pictures of t he lun ar frontside in this book were alltaken near the sunrise terminator,so that the Sun was low inth e east. Th e solar elevation at the center of each frame is alsogiven in t he P hoto Reference Table. In viewing-these picturesfor th e first time, m any people have difficulty in distinguishingbetween protuberances and indentations. This can be clearedup by rememb ering th at t he direction of illumination was fromth e right (ea st). Some viewers find it helpful to hold th e bookso tha t a window of the room is at th e right side.The farside pictures were taken near the sunset terminator,so that the Sun was in the west and the direction of illumina-tion was from th e left. (For th e purpose of this discussion, th eseries of pictures of t he Mare Orienta le region, a t th e Moonswestern limb, are considered frontside pictures.)Some of th e pictures sho w white lines or bars th at are per-pendicular to th e framelet lines. They are no t likely to beconfused with actual lunar features. Th e short ones that onlyextend across indiviual framelets are caused by momentary

sitpal dropouts during the readout and transmission of thephotographs. Th e long, very thin ones are caused by scratchesin th e spacecraft film.The careful viewer may see a p atter n of tiny white crosses(in th e sha pe of plus signs) across most of the pictures. The yappear most distinctly in shadow areas. Thes e are reseaumarks, which were preexposed on the film to aid in thephot ogra mmetr ic recovery of the original exposures geo-metrical relationsh ips. Th ey were used on all missions exceptthe first.Th e pairs of sharp-edged white triangles on a few of th epictures ar e artifac ts produced by the film-processing equipment.There are several types of irregular white marks which arecaused by processing blemishes on th e spacecraft film. Someare roughly circular, and some resemble asterisks. Atten tionis called to them in the captions wherever it seems likely thatthey could be confused with lunar features. Th e captions alsopoint out areas of processing freckles.Nearly all of the pictures in this book are portions of singlephotographs. In a few cases, mosaics of two photogra phs wererequired to show some feature completely. Th e junctio ns be-tween pho tograph s on these mosaics were made straight,so thatthey will not be mistaken for natural lunar features. Th eframelet lines are, of course, offset at the se junc tion lines.

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C H A P T E R 2A

DISTANTV I E W

Most of th e pictures in this book are closeup photographs th atshow l unar feat ures a t levels of detail from 10 to 1000 timesfiner than can ever be photographed through an Earth-basedtelescope. Before examining these pictures in detail, it isinstructive to see the Moon as a whole; to understand theregional background within which each feature is set.Th e set of pictures tha t make up this chapter covers nearlythe entire lunar surface, with a substantial overlap betweenindividual pictures. Th e general plan of organization is tofollow the Su n around, starting a t the eastern limb (as seenfrom the Ear th) , proceeding westward across the more familiarvisible side to the western limb, and continuingwestward acrossthe farside to complete the journey where it started. In thecourse of this sweep, attent ion shifts between t he norther n andsouthern hemispheres, and between polar and equatorial zones.Each picture covers a broad enough region to exhibit theeffect of th e gross curv ature of the lunar sphere. Each front-side frame is vertical at the center, with the surface progres-sively foreshortened away from the center. Many of the farsideframes are obliques in which the camera, flying on the nightside of th e Moon, was faced westward t o photograph the illumi-nated region beyond th e sunset terminator.Wherever two or three pictures have been placed on onepage, it appears more natural to place the westernmost pictureon th e left side. Therefor e, if the reader wishes to proceedsteadily in the westward direction, he should see the right-hand picture and its caption first.Wherever t he captions name features tha t will be seen ingreater detail later, the names are printed in italics. Th ecaptions for this chapter do not directly indicate scale becauseof th e great variation in scale across the pictures. Instead.wherever practicable, the dimensions of some feature visiblein t he pic ture are given in the caption. Frontside crater di-mensions were tak en from the System of Lunar Craters, a catalogprepared by the Lunar and Planetary Laboratory of theUniversity of Arizona.The dimensions a nd locations of farside features were scaledfrom the Provisional Edition of th e Lun ar Furs i de Chart (LFC-1)produced by the -4eronautical Chart and Information Center.U. S. Air Force. Th ey should all be regarded as approximateat this time.With regard to farside regional desimations, it should benoted that the 180" meridian marks the middle of the farside.Th e region th at extends eastward from there to longitude 90"Wis called th e "eastern farside." Similarly. th e "western farside"extends from the 180" meridian westward to longitude 90" E.

Th e east ern limb area in th e northern hemisphere. Mare Smythii(G22) straddles the equator at longitude 90" E . North of it isMare Marginis (F20). and west of that, at the terminator, isthe circular Mare Crisium (A19). Mare Humboldtianum (C9)isabout latitude 55" N. Th e north pole is at C2.I


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Th e eastern limb are a in th e southern hemisphere. T h e dark walled basin at G20, with its spectacular radiatin g clefts, ispatch at I2 is Mare Smythii. Th e crater Humholdt (G7) is 200 located abo ut 70" S , 130" E. The very prominent craterkilometers in diame ter. Th e large irregularly-shaped. dark area Tsiolkousky (011) s due north of it, about 20" S. 130" E. Bothsouth of Humboldt is Mare Australe. Th e unna med, double- will be seen in detail in the next chapter.8


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Th e eastern regions of th e northe rn hemisphere. Mare Crisiumis at P14.and Mare Humboldtianum at L4. Th e crater Endymion(K7) is 125 kilometers in diameter. Northw est of the craterHercules (J10) s Mare Frigoris. Th e dark patch at N8 is (N18)mark approximately the 45" East meridian.

Mare Struve. Th e crater Posidonius (114) ies between LacusSomniorum t o the north and Mare Serenitatis to the south andwest. Th e craters Atlas (K 9). Macrobius (M15). and Turuntius

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~~

Th e eastern regions of th e southern hemisphere. Th e 60Eastmeridian may be traced by the craters Langrenus ( K 4 ) , Petavius(57, 177 kilometers in diameter ). Furnerius (110). oussingault(E18),and Demonax (E20). Th e great gash running southeast-

ward from Mare Nectaris (whose center is at D4) is the Rheitavalley. It is shown here in relation to i ts counte rpart, the pre-viously unknown valley th at runs northwa rd (H2 1 to119) fromthe double-rimmed depression at th e bottomof the photograph.10


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Th e central zone is her e viewed from nearly the same directionas it is seen from Eart h, but th e perspective is different. MareImbrium,at upper left, is outlined by its great circular mountainrim. Mare Sere nitat is ( N 7 ) is also circular, with a more subdued

border. Below them is Mare Vaporum, with the crater Maniliusa t L11. The small patch of mare below that, at J16, is SinusMedii. which is at the center of the frontside. Th e craterPtolemaeus (J19) is 153 kilometers in diam eter.11


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Th e no rth polar region as viewed from above. T he sunrise termi-nator runs along the 31" West me ridian , crossing (from south tonorth) Mare Imbrium and Mare Frigoris. the craters Philolaus(ElO) and Mouchez (Fa),and the north pole ( G 5 ) . ust outsidethe crater Peary. Beyond ther e, it becomes the sunset termi-nator, running southward along the 149' East meridian on th efarside. Th e crater Nansen (15) is 110 kilometers across,Rarrow (H11) is a crater with a notably square outline.

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Th e south central region. Th e sunrise terminator is about 24"W . The 0" meridian crosses the craters Ptolemaeus (J4),Walter(19). and Moretus (E18. located 70" S ) . Th e crater Pitatus (F7),marking the southern edge of M a r e Nubium, the very fresh

crater Tycho (F11).and t he 225-kilometer-diameter crater Clavius(D15). lie to the west. To the east are the craters Maurolycus(513).Manzinus (H19). Scott (E21). and A mundsen (E22). Th esouth pole (D21) s near the last-named crater.13


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1I , = I H

th e 40"West meridian is mainly mare terrain.with its widespread rays from K e p l e r (E13)d Aristurchus (B9). covers most of the picture. Sinus Iridumis the semicircular bay at the northwest edge of Mareium. Th e crater Euler (GS) s 27 kilometers in diameter .

The 10" West meridian passes through the crater Pluto (D2).which is 100 kilometers in diameter, and just east of th e cratersEratosthenes (Ell) nd Pitatus (E22). Rays from Copernicus((213)are spread across Sinus Aestuum to the east and MareImbrium to the north. Th e crater Lansberg(A16)ison he equator.15


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Running southward from the vicinity of Kepler (E.51,th e 40"Wmeridian crosses the crater Cussendl ( D E ) , which is 64 kilo-meters across, then t he circular MareHumorum. In t he highlandregion to the south. it crosses th e crater Schiller(D21). Schiller.a t 5 2 " s . is distinguished by its footprint shape.

The zone lust west of the center, mainly in th e southern hemi-sphere. Within Mare Nubium are the Slruighi lthll (E14). 12 0kilometers long. and t he crater Bullialdus (B13). Ranger VI 1made th e first closeup photographsof the Moon at B10, in MareCogniturn. Ranger IX photographed the crater Alphonsus(G11).16


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Th e western limb area in the northern hemisphere. Th e sunrise Th e western portion of Oceanus Procellarum. with its wide-terminator runs along the 98" West meridian, from the Cordillera spread, irregular bright markings near the craters Ssleucus (D9)Mountains (C22) to the no rth pole (A2). Note th e intersecting and Reiner (G13) . Th e dark-floored crater Grimaldi (D17) isrille patt ern s crossing the craters Repsold (D9) and Galvani about 220 kilometers in diameter, and can be considered as a(C10) . Th e crater Pythagoras (D6) is 128 kilometers across. small circular mare. Th e terminator is at 80"W.17


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The western limb area in the southern hemisphere. Th e centerof .\/ore Orientale (D5) s loca ted abo ut ZO"S.95"W.The prominen tcrater Hausen at C17 is about 65"s. 90"W. The light-flooredcircular plain just southeast of it (D19) is Bailly. which is300kilometers in diameter.

The southern hemisphere centered about 7O'W. Th e elongatedfeatures of sculpture and deposition radiating from MareOrientale are appare nt at upper left. Th e dark-floored craterSchickard (F13) is 230 kilometers across. A very sharp rilleruns between the craters R yrg ius (F7) and Sirsalis (H5).18


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Th e bulls eye at the center of this spectacular view is thehlare Orientale basin (t he name Mare Annulatum has also beenproposed), on th e extreme western edge of the visibleside. Thr eecircular scarps surround the inner basin, which is partially filledwith m are material. Th e outermost is the Cordillera Mountain

scarp, almost 900 kilometers in diameter. Th e craters Schliiter(581,Riccioli (M8) . and Inghirami (L20) are all located withinth e area that was blanketed by deposits of mater ial ejected fromOrientale. Detailed views of characteristic portions of th e basinar e shown on pages 125 through 131 .19


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Th e north ern region of the easte rn farside. Th e large circulardepression cen tered on E12 is more tha n 250 kilometers across,and is located about 58"N. 150"W. Its floor lacks the smoothdark-toned surface seen in maria. Such basins are somewhatmore abu ndant on the farside than on th e frontside.

The northern region of th e eastern farside. Th e north pole isat H3. The basin at C10 is quite inconspicuous in this photo-praph, where the terminator is at 99"W, although it was verydistinct on the photograph to t he left, where the terminatorwas 30" further west.21


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Northern zone of the western farside. Mare Moscouiense. C16.is shown again on page132. Th e circular depression at D8, about200 kilometers across, is located about 45"N. 150"E. Except forthe p atch of dar k mare material on part of itsfloor, it resemblesother farside basins. Th e terminator is a t 172"E.

Th e norther n zone at th e middle of th e Moon's farside. Thechain of four craters at F3 runs along the 180" meridian about65"N. The large crater at C20, which is about 100 kilometersin diameter, is located on the same meridian at 30"N. T h eterminator is at 164"W.26


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Souther n zone in th e middle of the farside. The crater at G12, Sou ther n zone just east of the middle of the farside. Th eabout 200 kilometers across, is near 175%. The termi- crater at D9 is located about 40"s. 170"W. Th e apparentnato r is at 172"W. Thi s region is unusual in the extent to which smoothness of its floor suggests a comparatively recent flooding.depressions are flooded with dark mare material. Note also the Th e crater with a central peak at E16 is located about 52"s.areas of bright discoloration in the maria, as at F2 an d D8. 170"W. The terminato r is at 156"W.27


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Th e equatorial zone of th e western farside. T h e crater a t I11 Th e basin a t bottom center is about 270 kilometers across. Itsis located about 5" S , 150" E. Th e terminator is nominally at floor is quite rough, and is itself devoid of mare material.164" E, but th e pronounced roughness of this part of theMoon However, th e bottom of the crater excavated in tha t floor a tproduces great loops and indentations i n t he visible terminator. H19 s flooded with mare material.28


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20-

21iSout hern zone of th e western farside. Since this is an obliquePhotograph facing southward, it can be viewed in its naturalPerspective by holding the book upside-down. T he termina tor isa t 174" E. The mare-filled crater Jules Verne (C16) is distin-wish ed by t he sh arp escarpment near its eastern edge. This

feature, which might be compared with t he frontside'sStraightHhll (page 105).consists of a numb er of straig ht segments withdistinct changes in direction. Th e crater with a central peaka t 53 s located about 10"S, 160"E. Th e concentric-ringed basina t I2 1 is 1400 kilometers to the south, at 55" S, 160" E.29


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The equatorial zone of the western farside. The prominent line. The line points to the crater ?sioNtovsky (520) .more thanbasin at 0 3 is located about 5" N, 140" E , and is about 300 800 kilometers away at 20" S. 130" E. The region between thekilometers across. It s floor, which is devoid of any mare two is marked by other crater chains. Some of these, as at I l l ,filling mater ial, is crossed by a chain of craters in a precise are radial to Tsiolkousky. while ot hers (e.g.. J8) are not.30


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Th e northern zone of the western farside. Th e crater atD11 islocated about 40"N, 120"E. Th e terminator is a t 140%. T h elarge unnamed crater at D2, with rilles crossing the floor nearthe central peak, is located about 55"N.105"E.Th e northern zone of the western farside. Th e crater whosecentral peak is at E l 0 is located about 40"N. 145"E. The termi-nator is at 156"E. Mare Moscoviense (F19) s about 300 kilo-meters in diameter.

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Th e southern zone of the western farside. Th e terminator is at147" E. Like the other southward-facing oblique on page 29,this photo graph shows correct perspective when viewed upside-down. T he crater Tsiokocsky (K8) is located about 20" S, 130"E.

Some of th e remarkable fe atures of this conspicuous dark-flooredcrater a re shown in detail on pages 133 an d 134 . The central-peaked crater at B E is located about 28" S. 110" E. The largecircular depression a t K21 is centered about 55" S, 130" E.32


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just beyond the eastern limb area. Th e116' E. Th e left third of th e photographons of th e eastern limb that were pointed out at thef this chapter. Mare Marginis is at the top. The(A3). which is 1 4 2 kilometers in diameter, is9" N, 84" E. Mare Smythii. centered at B7, resem-a considerableghost rings." T he cra ter Gibbs (B17) is at thehe secondary c rate r chains a nd deposits of ejecteding from the large crater Humboldt. whose nort h-

ern rim is seen at B20. Th e interior of Humboldt is shown inmore detail on page 96.The eastern half of this photograph covers th e area seen sostrikingly in the oblique picture on pages 34 and 35. with theEa rth in the background. T h e basin centered at K13 (locatedabout 12" S. 105" E ) is exhibited he re a s a very distinct depres-sion. It is abou t 250 kilometers in diameter. In the obliqueview. where it occupies about half the length of the picture,the evident roughness of the floor almost completely obscuresthe height and continuity of the rim.


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This Lunar Orbiter I photograph, taken August 23, 1966. at4:36 p.m., Gre enwich Mean Tim e. was our first view of th e Earthfrom th e vicinity of he Moon a nd also provided our first detailedoblique view of the lun ar landscape. The spacecraft was380,000kilometers from the Earth and 1200 kilometers above the lunarsurface. At th at time th e sunset terminator on Ear th was nearOdessa in th e Soviet Union and Istanb ul, Turkey, and passedslightly west of Capetown. South Africa. Th e Earths South Polewas within t h e field of view but on t he dark side of th e erminator,

as it always is in August.The homeward look emphasizes the spatial relationship be-tween t he unmann ed spacecraft and th e farflung mission opera-tions team that controlled it. It was rnidmorning a t the SpaceFlight Operations Facility in Pasadena, California, and at thenearby Goldstone tracking station, where t he Moon was not dueto rise for another 3 hours. At th e Woomera, Australia trackingstation, where it was th e middle of the night, t he Moon had justset. Th e Moon was high in the midafternoon skyat th e station

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near Madrid, Sp ain, but the spacecraft was about to interrupt allcommunication by going behind t he Moon.Th e portion of t he Moon seen in this photograph (which coverstwo -th irds of th e original high-resolution f rame) lies with in thefarside region that is shown in vertical view on page 33. Thecenter of this photograph, located about 10" S, 105" E, corre-sponds to K12 in t he vertical photograph. As the camera wasfacing westward, north is to the right. Th e horizon coversabout550 kilometers from north to south.

With t he S un nearly overhead, very few lun ar surface feature scast shadows. Eve n so, the oblique view conveys a strongimpression of th e roughness of the surface. Th e lighting on theinterior walls of cr ater s suggests a general relationship in thisarea between the a pparent freshness of th e craters and th e reflec-tivity of their wall materials. Tho se craters tha t are not notablymodified by later cratering or slump ing generally hav e brighterwalls. Th e upper part of the crater wall commonly appearsas adarker horizontal band.

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C H A P T E R 3A

C L O S E U PVIEW

Mans early interest in the Moon is recorded largely inmythology. Ancient Egy ptians honored th e Moon as their godThoth (Dhouti),god of wisdom andmagic. T o he ancient Greeksth e Moon was their goddess Selena. from whose name th e termselenology (study of the Moon) is derived. Even those civiliza-tions that did not worship the Moon fixed their religiousfestivals in term s of t he 29%-day cycle of visible pha ses whichconstitutes the lun ar month. With t his awareness, a great dealof accu rate information was accumulated in ancien t times aboutth e motions of th e Moon with respect to oth er celestial bodies.Galileos application of the telescope to the Moon in 1610marked t he birth of a new a rea of science, selenography (studyof lu nar surface morphology). Observation of t he Moon, usingtelescopes of various sizes and optical designs, has continuedto th e present t ime at many observatories aro und t he world.

Two factors limit what can be accomplished by telescopeobservation. Instability of th e Earths atmosphere has preventedobservations of l unar detail finer tha n a few hundred meters.Because th e Moon always presents nearly t he same face to theEa rt h, a fixed viewpoint is imposed on the observations. Withinthe past 10 years, photography from spacecraft ha s circumventedboth of these limitations.Th e photographs of the western farside transmitted to Earthfrom th e Soviet spacecraft LUNA 3 when it flew past th e Moonin October 1959 freed selenography from its fixed viewpoint.Man s first closeup view of the lunar surface was provided byth e American spacecraft Ranger VI1 July 31,1964. Photographstransmitted from soft-landed spacecraft, particularly theSurveyor missions, more recentiy have shown us local detailsat th e millimeter scale. Th e Lunar Orbiter photographyrepresents the largest single advancement in selenography todate.

To display all that was revealed by Lunar Orbiter photog-raphy is beyond t he scope of this book. A modest photocollection of lun ar surfa ce deta ils is pres ente d, beginning with

closeup views of th e frontside, grouped i n sections und er fourheadings: Maria; Highlands; Craters; and Faults, Rilles, andDomes. These sections are followed by a selected group ofdet ailed views of t he farside.MARIA

Since the 17th century, when they were actually consideredto be oceans, th e dark ar eas of th e Moon have been calledM aria(plural of th e Latin mare , sea). Luna r surface materials havebeen found, in general, to be poor reflectors of light, with thebrightest spots on the Moon reflecting about 20 percent andth e darkest regions as little as 5 percent of t he incident sunlight.A quantita tive basis for differentiating between th e two majorsurface units of th e Moon, the relatively da rk mare regions orseas and th e relatively bright t errae or highlands, is providedby comparisons of their albedo (the ratio between the lightreflected from an unpolished surface and the total light fallingon it).Oceanus Procellarum, the maria Crisium. Fecunditatis,Frigoris, Humorurn, Imbrium, Nectaris, Nubium, Serenitatis.and Tranquillitatis on the Moons frontside and the mariaOrientale , Moscoviense, Australe, Marginis, and Smythii on itslimbs and farside, together with several smaller regions, con-stitut e th e dark. relatively flat an d smooth area s of the lunarsurface. Many of th e maria ar e approximately circular. MareImbriu m, th e largest of th ese fe atures, is abo ut 1300 kilometersacross and can easily be seen with t he na ked eye when th e Moonis full. There does not appear to be any shar p distinctionbetween th e circular maria an d individual crate rs with mare-filled floors. such a s Grimaldi.The photogaphs provided on the following pages displaysome of the salient characteristics of mare surfaces, with specialemphasis on those observed near the candidate Apollo landingsites.

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Thi s oblique view to the southwest shows part of th e extensivemare of Oceanus Procellarum. Th e smooth plain is pitted withsharp-walled craters in the foreground. A wrinkle ridge isvisible extending diagonally across the mare to th e small craterDamoiseau L . Th e a rcuate cliffs (up to 1300 meters high) at th e

mare-highland s boundary in th e middle background are marked-ly evident. Behin d the rig ht-han d cliff is th e crater Damoiseau,located about 5"s. 1'W. This crater, with its intricately crackedfloor 37 kilometers across, is seen to be in th e middleof a largercrater, about 65 kilometers across.40


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.. I' # - - I CI 6 . .. 9 ,i. *' * :

* a 1 4 . 0

-

f long. arcu ate , branching ridges is evident in the15 about 350 lulometers inThes e ridges extend across the mare plain from t heGassendi in the upper center almost to the crat er Vitellolower center. Th e left-hand ridge is about 200 kilometers 38"30'W. Framelet width 86 kilometers

long. but only 8 to 16 kilometers wide Th e dark mare materialfilling the basin nearly obscures one crater in th e lower cente rThe arcuate rilles close to the lower right edge run approxi-mately concentric wlth the basin borders. Location 23"30'S,

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A highly sinuous, locally stee p scarp can be seen along th e scientists. The crater density on the flow appears to be thescalloped edge of a flat-topped plateau in the middle of Mare same as that on the bordering mare plain, and sharp-walledImbrium. Th e lobate shape of the plateau is similar to th at craters are common on both. Location: 32" N, 21"50' W.of some terrestrial lava flows and is so interpreted by lunar Framelet wi dt h 5 kilometers.

Th is high-resolution mosaic shows part of the stee p scarp of th eflow front illustrated above. Th e scarp for its rntire lengthappears to be somewhat rounded and smooth in profile No out-crops or rock ledges are visible along th e scarp. nor are an y

blocks of rock evident around the many s m a l l sharp-walledcraters alona the rim of the scarp. Details of th e flow front ap-pear to be well preserved. Location: 32"20' N . 22" W. Frameletwidth: 650 meters.44


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The wrinkle ridges extending across the picture are near acandid ate Apollo lan ding site in Oceanus Procellarum. Thi smoderate-resolution photograph shows the ridges as smooth,rounded features, with some local areas of steeper relief. T h e

ridges broaden a nd thin irregularly, but all decrease in breadthnear th e ends. Crater density is about the same on the ridges ason th e mare plain, and bright, sharp-walled craters ar e commonon both. Location:3"50'S, 6" W. Framelet width: 3.4 kilometers.

A high-resolution photograph of th e wrinkle ridge visible at theextreme left side of th e picture above. Th e ridge top is generallysmooth an d rolling. but its crests and sides are steep and abun-dantly strewn with blocks of rock. Blocks are concentrated

around several craters on the upper ridge crest, especially th ebright. sharp-walled crater at t he left center of the picture. I nthis case, the blocks appear to be a product of the cratering event.Location: 320 ' S, 36"IO'W. Framelet width: 450 meters.46


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! '

I ',


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of this sinuous mare ridge lies a cand idate Apollo density on th e ridge appears to be equal to th aton he adjacentSinus Medii. Th e ridge is rounded a nd subdued mare plain. Most craters are subdued, and some below th e ridgeNo blocks of rock ar e visible are essentially smoothed out. Location: O"10'N. O"5O'W.sharp-walled crate rs on the ridge. Th e crater Framelet width: 440 meters.


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cs

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HIGHLANDSThe relatively bright, rough, and elevated lunar surfaces arereferred to as terrae or highlan ds, to distinguish them fromth e relatively dark, smooth, and low-lying maria. Much of th ehighland area, thou gh rough, is actually a much modified plain.Morphologic featu res t ha t originally were sh arp commonly havebecome subdued with time. In part, this subdual is ascribedto the movement of loosely consolidated material from higherpositions to lower levels on the surface under the influence oflunar gravity. possibly with th e aid of moonquakes. Th e result-ing texture, whe re it is gentle an d does not involve large debrisflows, is referred to as patt ern ed ground. Several examples ofpatterne d ground, which is visible only on high-resolution pho-tographs, are shown in t his section.Mountain ranges exist on th e Moon in t he form of arcs, asso-ciated w ith t he major circular basins and bounded on th e sidefacing th e basin by steeper slopes or scarps. They form a con-tinuous border aroun d basins such as Mare Crisium. Others

form a discontinuous array, as exemplified by the Ju ra , Alps,Caucasus, Apennine, and Carpath ian Moun tains bordering MareImbrium. Still other arcs, such a s th e Altai Scarp, are in thehighlands but ap pear to he concentric with a nearby mare basin,in this case Mare Nectaris. Many mou ntai ns of lesser magn itudeoccur as isolated blocks or peaks.Concerning the relative age of th e highlands and t he maria,most scientists believe that the highlands represent older seg-ments of the lunar surface. Age dating (by isotope abund ances)of representative samples from both types of terrain is plannedfollowing the re turn of samples by th e Apollo astron auts.52


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h

General view of the Apennine escarpment at th e southeasternborder of Mare Imbrium. Resolution in this view is roughlyequivalent to th at ob tained with a large telescope on Ear th ona night wi th good seeing conditions. Some of th e peaks in theescarpment rise more than 2000 meters above the mare floor.Location: 20"30'N. 3"30W. Framelet width: 89 kilometers.

View of the Caucasus Mountains (lower center) and the cratersEudoxus (upper center) and Aristoteles ( top). Th e ruggedCaucasus peaks, up to 4000 meters high, are a continuation ofth e Apen nine Mountains (opposite) and border th e eastern sideof Mare Imbrium. Location: 42"30", lO"35'E. Framelet width:97 kilometers.53


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Oblique view toward the west showing Alpine Valley and MareImbrium ( top) an d t he isolated mountain block Pic0 (top right).Alpine Valley, about 150 kilometers long and 8 kilometers wide,is a unique feature on the visible face of the moon and gives

th e ap pearanc e of a terrestrial valley cut by a winding river(sinuous rille). Th e genesis of th is featu re will und oub tedl yprovoke considerable discussion in the future . Location:48"15'N, "E.54


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Oblique view, looking southwest, of the eastern side of theAltai Scarp. Th is portion of the sc arp, seen in the middleforeground, rises above its base an average of loo0 meters.Brightness of the slopes facing the camera makes it difficultto observe the detail on much of the scarp. Location: about26"E.28"s.

Representative details of the northern borders of Mare Sereni-tatis. The upper portions of th e p hotograph show hillocks andhummocky ter rai n of unkn own origin composed of light-tonedmaterials. Part of the Calippus Rille extends northe astwardfrom the lower center in the darker, smooth mare material.Location: 37"5O'N,13'555'E.Framelet width: 6 kilometers.

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View of th e crater Murchison. center (5 8 kilometers across) andUkert, u pper center, looking north toward th e southern edge ofMare Vaporum in th e background. Th e many irregular positivefeatures on the floor of Murchison, which may be attributed tovolcanism, are dissected by a network of rilles. Some of th e

rilles are sinuous and others linear. Th e prominent lineationswhich may be observed near Ukert have a pronounced north-west-southeast trend: these have been attributed to throwout(ejecta) from the Imbrium event farther to the northw est.Location: about 5" N . O"30' W .56


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Portion of a crater cha in close to the southern rim of the look, and the patterned ground is not strongly developed. Ancrater Abulfeda. Th e shadowed area in the lower center of the almost complete absence of large blocks is characteristic of thispho togr aph is par t of a small rille connecting the elongate chain, for which a n in terna l origin has been suggested by somecraters Abulfeda T, to the left, and Abulfeda X. to th e right. lunar geologists. Location: 15S, 1355E. Framelet width:Th is part of the Southern Highlands has a very subdued 410meter s.57


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Patt ern ed ground in th e crater Gassendi. T he textures are and also the abundance of large blocks on the crests of th e hillssimilar to other highland areas where th e patterns are strongly in th e upper right. Some of these blocks are more th an 10influenced by the slopes. Note the increase in crater frequency meters across. Location: 1915S, 4Oo05W. Framelet width:in th e shallow valley floor, at th e middle left of th e photograph. 560 meters.59


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Patterned ground in the Alpes Mountains north of Rima frequency is significantly less on the ridge slope th an on th ePlat0 11. This terrain has anotab le northeast-southwestpatte rn flatter areas above or below th e slope. A small circular feature,in the surface topography. Note also the appa rent change in perhaps a ghost crater, can be seen in the lower left. Location:coarseness of th e pattern at the break in the slope. Crater 49"15'N,1 Framelet width: 1 kilometer.61


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CRATERSA cr ater is a circular, polygonal, or elongate topographicdepression, generally with stee p inner slopes. Craters aboundon the surface of th e Moon an d Mars and, to a lesser extent,the Ea rth . Lunar craters range in size fromthe microscopic u pto more than 100 kilometers in diameter. Th e individual cratersshown in this section are arrang ed i n ord er of increasing size,starting with one nearly 4 kilometers in diameter.Although scientists have genera ted a voluminous literatur eon the subject, th e origin of craters is still controversial. Priorto the availability of closeup photography, many scientistsbelieved th at most craters were formed by the impact of meteor-ites and comets, while others felt that most of them were theproducts of volcanic activity. While the Lunar Orbiter photog-raphy has provided seemingly incontrovertible evidence for theexistence of bo th impact an d volcanic craters, th e relativeimportance of th e processes is far from settled.Lunar craters abound as single features, randomly distributedon the surface. However, many o thers occur as pairs, clusters,an d chains. Some examples of these are presented at th e endof this section.The relative ages of lunar craters are hypothesized fromtheir shapes and the appeirance nftheir rims, walls, and loorsWhat are thought to be young impact craters may display asharply raised rim, steep in ner slopes, and a d eep, sculpturedfloor. Older craters may show subd ued and ro unded rims, gentleinner wall slopes, and evenly filled floors. Some apparentlyyoung craters, believed t o be of volcanic origin, also displaysubdued runs. Geologists recognize other stru ctural details bywhich they may infer the relative ages of craters. In thefollowing examples, reference will be made to some of thesestructural and textural details as they were disclosed by thefive Lun ar Orbiters.

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The crater Mosting C (3.8 kilometers in diameter) is a very abound near the outer edges of the ejecta blanket. Th e crate rfresh crater with abun dant blocks on the rim. Th e ejecta is more nearly circular tha n it appears in this somewhatblanket is hummocky, braided, and dunelike, i.e., similar to oblique view. Location: l"30' S, 8" W. Framelet width: 1.7thos e of larger, fresh luna r craters. Second ary impact crat ers kilometers.63


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Part of the rim and walls of Mosting C. Large blocks up to about60 meters in length occur near th e rim. Th e steep crater wallsare characterized by talus slopes and outcrops of broken rock.Th ey resemble many stee p terrestrial slopes, including those of

some man-made crater s produced by explosives. T he freshnessof th e materials exposed in Mosting C was predicted on thebasis of Earth-b ased infrared studies. Framelet width: 220meters.

Transverse and radial dunelike textures north of the craterMosting C. Thes e are similar to base surge deposits produced onEa rt h by chemical and nuclear explosions and t o those aroundsome volcanos. Well-developed, discrete flows, such as thoseobserved around larger craters (e.g., Aristarchus), are lacking.Framelet width: 220 meters.

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a

c'1

7v

P. ..- . - - - *.- - . - - . . -The crater Copernicus H. 4.6 kilometers in d iame ter. is super-posed on the hummocky ejecta deposit outside the rim of thecrater Copernicus. It is surrounded by an apron of material th atis much darker than the bright ejecta blanket of Copernicus.

Th e dark apro n shows up best in full-moon photographs. Th ecrater also has an anomalously high infrared emission signaldur ing eclipse. Location: 6"50' N , 18"30' W. Framelet width:3.3 kilometers.66


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Secchi X. small, young crater (5.6 kilometers across) nearthe western edge of Mare Fecunditatis. Th e striking mottlingon the crater wall may be a result of differences in slopestability. Th e brighter areas appear to be steep surfaces meters.

from which fresh fragments may periodically slide downslope.T he darker ar eas may be flatter benches on which materialaccumulates. Location: 1" S. 43"40' E. Framelet width: 450

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Unnamed crater, 6 kilometers long, next to Rima Rode 11. origin. The freshness of this crater was predicted from itsThe great number of fresh blocks suggest th at th e crater is high albedo on full-moon telescopic photographs and from itsrelatively young. Th e elongate shape of this crater and th e infrared properties. Location: 13" N, 4" W . Framelet width:chainlike a line ment of th e smaller crat ers suggest a volcanic 45 0 meters.

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Gruithuisen K. a compound crater about 7 kilometers in diametersituated west of Mare Imbrium. It consists of inner and outersaucer-shaped depressions and an intervening ring of hillocks.Similar craters have been discovered in various parts of theMoon on Orbiter IV photographs. Th ey were probably formedby volcanic processes. The freckles at the bottom of thismosaic are processlng blemishes. Location: 3520N, 4240 W .Framelet width: 700 meters.

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A crater near Gruithuisen K (an d nearly as large) has internal of shar p, funnel-shaped crat ers 100 to 20 0 meters across.domal struct ure s like those of Gruithuisen K. Th e "domes" and Craters smaller than tha t are found with about equal frequencythe irregularly rectangular outline of the crater speak strongly on t he floor and on th e surrounding terr a surface. Location:for a volcanic origin. The crater floor also exhibits a number 35"30 N, 4 2 " 2 0 W . Framelet width: 700 meters.

Dawes, a young, 18-kilometer-diameter crater between MareSerenitatis and Mare Tranquillitatis. displays many featuresusually at tri but ed to impact. Consolidated bedrock is exposedjust below the rim crest; talus close to the angle of reposemakes up the rest of th e wall. Blocks up to 150 meters across

occur on the sparsely cratered rim. A dense secondary craterfield occurs beyond the rim, mostly outside the area of thephotograph. The crat er has an exceptionally high emission inth e near infrared during eclipse. Location: 17"lO' N , 26"20' E.Framelet width: 3 .6 kilometers.70


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An enlarged view of the norther n wall of the crater Dawes, Th e blocks seen on the talus slope probably originated a t th eshown at the bottom of th e opposite page. Bedrock in place consolidated rock ledges. Th e tracks of their downslopeis clearly seen along th e upper ledges of the wall. Tal us movement are partly concealed by th e fine talus. Frameletclose to the angle of repose makes the rest of th e wall slopes. width: 470 meters.

Detail of the floor of the crater Dawes. In the second framelet the crater. The arcuate structures near th e wall may be thefrom the left is th e contact between the floor and th e wall surface expressions of faults along which movement probablytalus. Several overlapping layers of notably blocky debris took place during the late stages of th e crat er formation.have slumped from th e wall and now overlie the original floor of Fram elet width : 470 meters.71


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An unnamed crater about 35 kilometers in diameter, located secondary craters which are typical of young, probable impactwithin the Orientale Basin (see page 128). Both the crater an d craters of it s size (for example, Aristarchus). These character-th e basin material s are fresh, indicating th at the crater is young. istics suggest that this crater is probably of volcanic orisin,The rim flank is smooth, and it lacks the blanket of ejecta similar to those structu res on Earth known as Calderas.grading outward from hummocky to radial and the fields of Location: 18"S, 91"W. Framelet width: 11 kilometers.72


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Oblique view of the crater Kepler. 32 kilometers in diameter.Th e blocky rim, radial ridges, and field of satellite craters ar etypic al of relatively youn g craters of probable impac t origin.

Crater Vitello (4 5 kilometers ac ross), at t he south edge of MareHumorum. The cracks on th e floor are relatively fresh andyoung, hut the crater itself could be either young or old. Ifyoung, it is no t of impact origin. because ejecta an d secondarycraters characteristic of young impact craters are not presenton th e mare just north of th e crate r. Lo cation: 31"S . 37'40' W.Framelet w idth: 5.4 kilometers.

Kepler and its related features are superposed partly on mareand partly on rugged te rra t ha t may be part of the outer rimof the Imbrium Basin. Location: 8" N . 38" W.

Trac ks mad e by bou lders, possibly set in motion by moonquakes.as they rolled downslope from the c entr al peaks of Vitello. Th elarger track. which is ab out 25 meters wide, shows a repetitivepattern imprinted by the rolling of an irregularly sha ped mass.Study of nearly 400 such boulder tracks noted to da te is providingnew insight int o the mechanical propertiesof th e lunar surface.

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Part of the floor of Aristarchus which resembles, in many could be either of volcanic origin (especia lly the flat, fissuredrespects, the floors of some Hawaiian volcanos. Mounds, material) or debris slumped from the crater walls. Location:complex fissures, and large blocks appear very fresh. These 23-30, N . 47"lO' W . Framelet width: 550 meters.

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Concentric fault scarps an d stepp ed surface s are common fea-tures on the walls of large lunar crate rs. Here in Aristarchus.par t of th e origin al rim has been displaced down ward towardth e crater floor. Large blocks up to 115 meters long occur nearth e crater rim. Location: 23"50' N , 47" W . Framelet width:550 meters.

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Large blocks, radial fractures, and concentric ridges charac-terize the surface near the rim of Aristarchus. This surfaceappears to be locally stripped of f i e material (which is, how-ever, present in the radial depressions) and radially channeledby materials ejected from the crater. Locat ion: 22"50' N, 47"W .Framelet width: 550 meters.

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Index map of Arista rchus showing locations of th e thre e flowfeatures illustrated on this page. On all thre e photographs. th ewidth of a framelet is 550 meters.A. One of several flows near the sout h rim of Aristarchus thattrends parallel to the crater rim. Here a leveed channel(upper left) disgorges bulbous ridges of flow material.

B. Thi s hairpin-shaped feature is one of th e many flowstructures on the south flank of Aristarchus. It resemblessuperficially some secondary impact craters farther from thecrat er rim. Unlike secondary crater s it is rimless, and onechanneled leg has both a levee and a bulbous flow deposit.

C . Flows with sinuous channels and marginal levees on thenorth rim of Aristarchus. T he flows may be debris, volcanicmaterials, or shock-melted material generated by a hyper-velocity projectile wh ich produced the crater. T he flows ar edemonstrably younger tha n th e surrou nding materials.79


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This photograph. one of th e most interesting taken by Lunar ridges and rilles, and the large numb er and linearityof its satel-Orbiter I, displays the crat er Taru ntiu s and its extensive field litic craters. However, the long, linear, tangential trough atof satellitic craters. Taru ntiu s (56 kilometers across) is anom- right center is probably u nre late d to Taruntius. Location:alous because of its relative shallowness, its intern al concentric 2-40' N , 47"40' E. Framelet width: 8 kilometers.80


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A general view of t he crater Ty cho, an excellent example of ayoung, fresh, lunar crater. A high central peak, slumpedwalls, and hummocky rim deposits are well-displayed typicalfeatures. In addition, the floor is extrzmely rough, with width: 7 kilometers.mounds and fissures. and th e rim has prominent flow struc turesan d a strong concentric texture in many places. Tycho. whichis 85 kilometers across, is located a t 43"lO' . 11"lO'W . Framelet

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Typical details of th e floor and floor-wall contact of Tycho, irregular ones have variable directions. A flow lobe in theincluding mounds, fissures, and blocks. Long fissures com- uppe r right corner has moved down th e wall and bulldozedmonly parallel t he floor-wall contact, while shorter, more its way into the floor material. Framelet width: 940 meters.82


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A view of some of the roughest parts of the floor of Tycho.Some geologists consider the symmetrical rings or shellssurrounding the large mounds to be due to the flowage of shock-melted rock off the surface of the mounds. Others interpretthem as volcanic domes. Fissures and blocks abound in all partsof th e floor. Framelet width: 940 meters.

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A represen tative segment of th e crater T ychos terraced walland n orth ern rim crest (located near the top of th e photo-graph). As is typical of fresh craters, the uppermost wallscarpis th e most pronounced. Th e level terrace surfaces are almostobscured by t he abun dant flow features, which are here prob-ably debris flows. Blocks are particularly abundant on t herim, although they occur on all surfaces. Framelet width: 930meters.

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Well-developed flow features just outside the north ern rim ofth e crater Tyc ho. Overlapping lobes, eman ating from a largechannel-and-levee system, flow north ward away from thecrater. T h e small-cr ater density variations on separate flowssuggest different ages. The flows, themselves, may have beenmolten lav a, volcanic debris, or partially fluidized impact ejecta.The cross at upper left marks the site of the Surveyor VI1spacecraft landing. Framelet width: 920 meters.

Pa rt of Tychos well-developed concentric rim pattern . Th epatt ern may reflect a fractur e system produced by th e crater-ing event. Notice also the abun dant blocks and the flat,smooth areas in topographic lows. Th e flat areas are pondsof either fine debris or volcanic materials that flowed andaccumulated in th e depressions. Located on the n orthern rim,directly east of th e opposite photograph. Framelet width: 920meters.85


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Th e rayed cra ter Copernicus, to the left, and th e unrayed craterErato sthen es. Both ar e relatively young, being superposedonthe mare and having fresh and extensive ejecta blankets andsatellitic cra ter fields; the su perposition of Copernicus ray sand secondary craters on Eratosthenes shows tha t Copernicus

is the younger. Other craters in the picture ar e partly filledby mare material a nd ar e therefore older th an th e mare.The arcuate mountain chain is part of a ring surroundingth e basin of Mare Imbrium. Location: 11" N, 13"W. Frameletwidth: 85 kilometers.86


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Th is mosaic composed of two medium-resolution frames providesa vertical view of Copernicus, a relatively young crate r withan extensive ray system. The floor of Copernicus is coveredwith an intricate pattern of hills, ridges, troughs, and sin-uous cracks. T h e less rugged northwestern pa rt (upper left)

has a lower albedo (i.e., darker tone) than th e rest. Th e ex-terior rim displays a complex juxtaposition of concentric andradial structu res and local smooth patches. Copernicus, 93kilometers across, is located at 9"40' N , 20" W. Framelet width:3.4 kilometers.87


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Detail of the floor of the crater Copernicus. Hills are littered drainage of loose material into subsurface fractures. Th efloorwith blocks; some have summit depressions. which suggests is covered with swales and depressions which appear morethe possibility of internal origin. Th e irregular cracks with subdued tha n those in th e floors of Aristarchus and Tycho.crater-shaped enlargements along them may have formed by Framelet width: 44 0 meters.88


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Wide-angle oblique view, looking due north, of the crater Co-pernicus. Blocky, rough ground jus t outside th e rim crest issurrounded by a series of smooth ridges approximately radialto th e center of th e crater. Th e keyhole-shaped crater Fauthis superimposed on one of t hese ridges 60 kilometers to the

south. In t he foreground, a complex array of mounds, cones,and crater clusters mark the outer portions of the rim. Th eclusters appear to have been formed by the impact of frag-ments ejected from th e large crater. Th e origin of the moundsand cones, however, is still a matter of controversy.89


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iew of the north wall of Copernicus. Patches of smooth abrupt ly at the floor in a nearly st raight line. A comparison oferche d at several levels. Two well-developed this photograph with the oblique view of the same area is help-th e western half of the picture. T he easte rn ful in visualizing th e three-dimensional relationships amongthe floor and the western one terminates th e various features. Framelet width: 3.4 kilometers.91


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k

Posidonius, a 100-kilometer crater a t the nor theastern edge ofMare Serenitatis. T he crater is partly filled and the rim partlycovered with mare material. Th e existence of an inner ringsuggests that the floor has been uplifted, probably by isostaticadjustmen t; the linear rilles may have formed by faulting dueto tension associated with the adjustment. An intricatelysinuous rille runs along the western edge of the crater floor.Location: 32" N, 30" E. Framelet width: 12 kilometers.

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The mare-filled crater Plato, 100 kilometers in diameter, nor thof Mare Imbrium. Th e mare material in Plato is like that out-side but is not connected with it at th e surface, suggestingeitherlocal subsurface sources for the mare materials or a subsurface

duct connecting the two. Th e sharp sinuous rilles tha t headnear Plato (th e one to th e southwest is double) may or may no tbe genetically related to th e crater. Location: 51"30' N , 9" W .Framelet width: 12 kilometers.93


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Gassendi. a 110-kilometer-diameter crater at t he no rth edge ofMare Humorum. Gassendi is younger tha n the distinctly circu-lar Humorum basin upon which it is superimposed, but olderth an the mare material th at fills the basin an d the peripheraldepressions of Gassendi's floor. Considerable uplift of the width: 4 kilometers.

floor, probably through isostatic adjustment, is suggested bythe numerous cracks and the unusually high elevation of th efloor and centr al peak relative to th e rim crest (quite similarto Posidonius, page 92). Location: 18"50 , 39"50'W. Framelet

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Humboldt, a large crater 200 kilometers across, having an un -usually regu lar system of fresh-app earing rilles o n its floor,resembling a spider web. Th e rilles cut across a complex ofmassive peaks near the center, a hummocky unit in the north-west part of the floor, and a light-toned plains unit covering

th e hummocks in th e southeast. Some rilles are filled in bythe dark mare material which occurs in patches around theperiphery of th e floor. Th e rilles may have formed as a result ofslow isostatic rebo und of the floor. Location: 26" S, 3" E.Framelet width: 12 kilometers.96


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The unusual craters Sabine (right, 30 kilometers across) andRitte r, at th e southwest edge of Mare Tranquillitatis. A pos-sible volcanic origin for these craters is suggested by theirrelatively high floors. arcuat e internal ridges. appare nt lackof secondary craters, and close resemblance to each other.These characteristics resemble those of terrestrial calderas.Similar crater pairs exist on the Moon's farside (see page 135).Location: l"40' N, 19"40' E. Framelet width: 1 2 kilometers.

A crater chain th at crosses light-toned plains-forming materialin the large old crater Davy Y (left) and continues eastwardinto the adjacent rugged highlands where it culminates in thebright crater Davy G (15 kilometers across). N ote t he markedlyuniform width and spacing of th e crate rs in this chain. DavyG cools anomalously slowly a t eclipse and appears to be a freshvolcanic crater a t the intersection of two fractures. Location:lO"40' S , 6'10'W. Framelet width: 12 kilometers.

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Detail of the crater Messier, Fresh blocks and possible out-crops of ledges occur along with slump structures on the wails.T h e dark material in the elongate depressions on the floorcould be accumulated debris from the walls. Messier and the

rays shown in the photograph on the opposite paae may havebeen produced by a low-angle impact, but the coincidence ofthe asymmetric rays an d the crater triplet remains to be fullyexplained. Messier is located at L350'S,7"40'E.99


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Rima Stadius IV, a chain of craters that is part of the fieldof abun dan t satellitic craters surrounding Copernicus. Narrowridges and troughs, and strings of small crat ers form anirregular herringbone pattern with the Vs pointing south-ward in t he general direction of Copernicus. Th is patternis seenin t he small craters th at surround many large, bright-rayedcraters. Location: 1630N, 620W.Framelet width: 450 meters.

Terrain northwest of the Orientale basin, including radiallystreaked material and numerous equisized, somewhat irregularcraters. Such crate rs are commonly arranged in chains radialto Mare Orientale. Th ey may be secondary impact craters ofthe Orientale basin or volcanic craters along impact-openedfractures. Approximate location:8N, 113W . Framelet width:about 25 kilometers.102


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FAULTS, RILLES , AND DOMESTh e three previous sections have included several examplesof such s tructural features as wrinkle ridges, fractures, shrink-age cracks, and slum p blocks. Th is section is devoted to three

other prominent types of structural features.Faults: A fault is a plane along which rock masses have beenshifted. Th e displacement may be horizontal, vertical, ordiagonal. A t places. the lunar surface gives visible evidence ofsuch displacement structures. T he Straigh t Wall (Rupes Recta)is a prominent example whose long, continuous escarpment dis-plays a vertical component of displacement of over 250 meters.Rilles: These are depressions on th e lunar surface th at bearsome resemblance to terrestrial valleys. Two general types arerecognized: linear and sinuous rilles, with a few combining thefeatures of both types. Many linear rilles appe ar to be depressedrock masses bounded by parallel faults. Large linear rilles areas wide as 10 kilometers a nd half a kilometer deep and mayexten d for hundr eds of kilometers across th e lunar surface withcomplete disregard for the preexisting surface features. Sinuousor meandering rilles usually are smaller though often as long.Commonly they head at a crater or similar depression. Th ey arecommon in some mare areas and ra re in highland areas. Sinuousrilles are generally similar in form to terrestrial stream channels,and many scientists believe that t hey were formed through theaction of particles carried by a fluid flow.Domes: Circular, raised stru ctures up to 20 kilometers wideand several hu ndred meters high abound on t he Moons surface,particularly in mare regions. Althou gh most previously knowndomes .were thought to possess smooth, flat surfaces, LunarOrbiter photographs have revealed t ha t many are characterizedby steep-sided, rough, and cratered surfaces. Both ty pes ofsurface are displayed by th e volcanic domes found on t he Ea rth .

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d

1i

The Straight Wall is a unique scarp on th e eastern side of MareNubium. It originated as a fault some 120 kilometers long, witha vertical displacement of about 250 meters. Thi s simple typ eof fault scarp is less common on the Moon than t he graben whichresults from the downw ard displacement ofthe rock mass betweentwo roughly parallel faults. Rima Rirt I (left) is an irregulartrough or rille, and not necessarily a graben. Location: Zl"50'5.8"lO'W. Framelet w idth: 12 kilometers.

A portion of Rima Sirsalis

the moon as viewed by lunar orbiter

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