JOURN^t.oF GF.OVH¾S•CAL RESF•ARC}• VOL. 73. No. 22, NOV•-MB•-R15, 196g

Principal ScienceResults from Surveyor 5

L. D. JAFFE,1 S. A. BATTERSON,2 W. E. BaowN, Ja.,1 E. M. CHRISTENSEN,1 S. E. DWORNIK,3 D. E. GA!JLT,4 J. W. L!JCAS,1 P•. I-I. NORTON,1 R. F. SCOTT,5 E. M. SHOEMAKER,6 G. I-I. SUTTON,7 ANDA. L. T!JRKEVICH8 The area of Mare Tranquillitatis in which Surveyor 5 landed appears to be similar to sites in Oceanus Procellarum. The gross elemental composition of the surface material and its responseto a magnet are similar to those of a basalt. The debris layer appears to consist of aggregates of the order of I cm in diameter consisting of fine grains and set in a matrix of less-coherentfine grains (most of them 2 to 60 t• in diameter) mixed with some rocky frag- ments I mm and larger. The static bearing strength is less than 104dynes/cm 2 for the upper few millimeters and averages approximately 3 X 105dynes/cm 2 for the upper few centimeters. The evidence suggeststhat chemical differentiation has occurred in the moon, probably owing to internal heat sources; this is consistent with the hypothesis that the maria are basaltic volcanic flows.

The area of southwesternMare Tranquillitatis the other giving some magnetic characteristics in which Surveyor 5 landed appears generally of the surface material with a bar magnet. similar to the sites in Oeeanus Proeellarum The three most abundant elementsfound by observedby Surveyors1 and 3. All three areas Surveyor 5 at the mare landing site are the are fairly level dark maria with rather similar same as the most prevalent on the surface of distributions of craters and rocks. A surface the earth; in decreasingabundance, they are layer of weakly cohesivefine particles, aggre- oxygen, silicon, and aluminum. The relative gates, and rocks is present in both Mare Tran- amounts of the chemical elements are similar quillitatis and OeeanusProeellarum. Differences to the amounts in a silicate rock of a basaltic between the surface layers in these maria are type. relatively small. Lunar surfacematerial of high magnetic sus- Surveyor 5 was the first soft-landing lunar ceptibility adhered to the magnet. The quantity spacecraft to obtain information about the of magnetic material observed on the mag- chemical nature of the hmar surface. This infor- net is comparableto that expectedif the mag- mation was obtained through two experiments, net came in contact with pulverized basalt with one giving the gross chemical compositionby 10 to 12% magnetite and not more than 1% an a-particle backscattering instrument, and admixed metallic iron. Particle size of material attracted by the magnet was less than 1 mm. Surveyor 5 landed in a dimple-shaped,9- • Jet Propulsion Laboratory, California Institute X 12-meter rimlesscrater, which is the largest of Technology, Pasadena, California 9,1103. member of a small chain of rimless craters; a 2 Dynamic Loads Division, NASA Langley Re- parallel row of very small craters also occurs search Center, Hampton, Virginia 23361. a NASA Headquarters, Washington, D.C. 20546. within the large crater. The long axis of the • Planetology Branch, Ames Research Center, large crater and the crater chain are approxi- Moffet Field, California 94035. mately parallel with the dominant linear fea- 5 Division of Engineering and Applied Science, tures in the highlandswest of Mare Tranquil- California Institute of Technology, Pasadena, Cali- fornia 91109. litatis and with many other elongate craters • Branchof Astrogeology,U.S. Geol•)gicalSur- and crater pairs in nearby parts of the mare. vey, Flagstaff, Arizona 86001. On the basisof its shapeand the alignmentof * Itawaii Institute of Geophysics,University of small associated craters, the crater in which Itawaii, Honolulu, Hawaii 96822. 8 Enrico Fermi Institute for Nuclear Studies and Surveyor 5 landed may have been formed by Department of Chemistry,University of Chicago, drainage of surfieial fragmental debris into a Chicago,Illinois 60637. northwest-trending fissure. 7165 7166 JAFFE ET AL.

Observationsof blocky rimmed craters,rela- of particlesby exhaustgases blowing along the tively nearby, indicate that the local thickness surface,and explosiveblowout of entrappedgas of the layer of fragmental debris with low co- and soil from directly beneath the nozzle im- hesion is not more than 5 meters. The walls of mediatelyfollowing engine shutdown. Analyses the Surveyor5 crater provideexposures of the of the disturbance indicate the material has a upper meter of this debrislayer. •Differenttypes permeability to gasesof between I X 10-8 and of fragments are revealed in the pictures of 7 X 10-8 cm•', which is comparableto the per- the debris dislodgedfrom the walls during the meability of terrestrial silts. landing and in the pictures of the undisturbed As for Surveyorsi and 3, the landingpro- parts of the wall. The types of fragments in- duced interactions with the surface. Various elude: analysesof phenomenaassociated with the land- ing and with the firing of the vernier rocket 1. Bright, angular objects,which are in- engines have provided these additional esti- ferred to be piecesof dense,rocky material. 2. •Dark, rounded objects, which are prob- matesof surfaceproperties. ably aggregates of very fine-grained particles. Static bearingstrength: 3. ])ark, lumpy objects, which appear to For upperfew millimeters,<104 dynes/cm 2. be aggregatesof aggregates. Averagedover upperfew centimeters,•3 X 105dynes/cm 2. The aggregatecharacter of some of the loose Angle of internal friction: consistentwith Sur- ejected fragments is well demonstratedby the veyor 3 results (37ø). presenceof bright angular chips set in a dark Pressuredeveloped by the soilagainst the foot- fine-grained matrix. At depths greater than pad in resistingthe slideduring landing was about 10 cm, most of the debris layer appears about7 X 104dynes/cm •', which agrees with to be composedof slightly compressedaggre- results obtained from the soil mechanicssurface gates, ranging from a few millimeters up to 3 samplerexperiment on Surveyor3. The esti- cm in diameter, set in a matrix of less-coherent mate of permeabilityindicates that most of the finer particles. Rocky chips and fragments particlesare in the 2- to 60-/•size range; this larger than a millimeter are dispersed as a valuesagrees with results from photographic ob- subordinate constituent of the debris. servationsof the disturbedareas, the matchof The estimated normal albedo (normal lumi- Surveyor5 footpadtrenches to trenchespro- nance factor) of the undisturbed parts of the ducedexperimentally in pulverized basalts, and lunar surface near Surveyor 5 is 7.9 ---+1.0%, analysesof Surveyor3 footpadimprints. Clods somewhat lower than observedat the Surveyor observedin the disturbedareas appear to be 3 landing site. Debris ejected on the lunar sur- similarto the onesobserved in previousmis- face in front of the footpads has a normal sions,indicating a similar cohesion. In general, albedo of 7.5 _4-1.0%, which is only about one- thesoil at thissite appears similar to, butsome- twentieth lower than the albedo of the undis- whatweaker than, the soil at theother Surveyor turbed surface but is similar to the albedo of the landing sites. material disturbedby the footpadsat the Sur- The lunar day temperaturesderived from veyor 3 landing site. Surveyor5 observationsare in fair agreement New photometric evidenceobtained from the with predictionsbased on telescopicobserva- Surveyor 5 pictures showsthat the bright an- tions. The temperaturesof the lunar surface gular fragments are denser or at least less after sunsetand duringtotal eclipsesuggest porous than the dark fine-grained surficial ma- that the surface material has an effective re- terial and dark aggregates.The surfacesof the ciprocalthermal inertia of approximately500 bright angular fragmentshave a photometric cm•' sec '/2 øK/g cal,in goodagreement with Sur- function more like that of a lambertian scat- veyor 3 eclipse data. This value differs from terer than like that of the fine-grainedlunar a value of approximately1000 obtained from material. data derived on earth. A spacecraftvernier engine firing against The evidence that the lunar surface material the lunar surface produced observable erosion at the Surveyor5 landing site is basalticin resulting from two mechanisms' the removal compositionand the fact that this Surveyor5 SURVEYOR 5--PRINCIPAL SCIENCE RESULTS 7167 site appearsto be typical of the mare areas are corona) at distancesof 10 to 30 solar radii from consistentwith the hypothesisthat the mare the center of the sun. Since the brightness is basins are filled with extensive basaltic volcanic producedby the scatteringof particulate matter flows. If such flows have occurred,some of the betweenthe earth and the sun, it shouldprove processesand products of lunar magmatic ac- possibleto derive density measurementsof par- tivity are apparently similar to those of the ticulate matter at distances out to one-third the earth. The results suggest that differentiation radius of Mercury's orbit. A good determination has occurred in the moon, probably owing to of the density distribution with height above internal sources of heat. the eclipticplane can be made. Surveyor 5 provided the first measurements (Received March 29, 1968; of the brightnessof the solar corona (the F revised July 15, 1968.)