Viking Lander 2 landed on a flat plain of fine‐grained sediment overlain by dispersed, evenly distributed boulders. The fine‐grained material is probably part of a high‐latitude mantle comprising material swept south from the polar regions. The boulders, which have distinctive deep pits, or vesicles, may be the residue of an ejecta deposit from the crater Mie. Alternatively, they may be the remnants of lava flows which formerly covered the region. Polygonal sediment‐filled cracks may have been formed by ice wedging, similar to the process that occurs in terrestrial permafrost regions. Alternatively, they may be desiccation polygons.

Viking 1 landed on volcanic terrain in the plains of Chryse. Stereo pictures reveal an undulating topography. Bedrock is exposed along several ridge crests. Blocks are more numerous than can be attributed to impact ejecta. The presence of an apparent variety of rock types suggests in situ weathering of extrusive and near‐surface basaltic igneous rocks along a linear volcanic vent. Fine‐grained sediment is present in drift complexes and isolated drifts. During the course of the Viking mission a small patch of fine‐grained sediment slumped down one of the drift faces. Otherwise, no morphological changes unrelated to spacecraft activity have been observed.

A total of 6315 pictures were taken by the television camera on Surveyor 3 after the lunar landing. These pictures have provided much new information about the location of the landing site on the moon, the detailed topographic and geologic characteristics of the lunar surface, and the appearance of the earth as seen from the moon, both during eclipse of the sun and during partial direct illumination by the sun. Surveyor 3 landed in a subdued crater slightly more than 200 meters in diameter, which has a low rounded rim and is about 15 meters deep. The spacecraft is situated on the east wall of the crater, about half way between the center of the crater and the rim crest. The spacecraft is inclined 14.7° ± 1.0° toward the west. The selenographic coordinates of the landing site are 2.94°S latitude, 23.34°W longitude, relative to selenodetic control adopted by the Aeronautical Chart and Information Center. Small morphologic elements of the landing site include small craters, linear ridges and troughs, and fragmental debris. The craters and fragmental debris resemble those observed at the Surveyor 1 landing site, both in distribution of shape and in distribution of size. Most of the craters in Surveyor 1 and 3 pictures are inferred to be of impact origin. Their size‐frequency distribution corresponds to the distribution that would be produced by repetitive bombardment by meteoroids, a bombardment sufficiently prolonged that the crater population has reached a steady state or has come to equilibrium. Some of the craters observed at the Surveyor 3 landing site are inferred to be of secondary impact origin, and some probably have been formed either by subsidence or by drainage of fragmental debris into cracks or fissures in the subsurface. Fragmental debris at the landing site is inferred to have been derived primarily by the same process of repetitive bombardment that produced the majority of craters. The inferred volumetric size‐frequency distribution of fragments, derived from the observed size distribution of fragments on the surface, is similar to the distribution that would be produced by repetitive bombardment of coherent rocks by meteoroids with a mass‐frequency distribution like that found from observed meteors and recovered meteorites on earth. Two prominent strewn fields of blocky debris were observed around two craters, 13 and 15 meters across, at the Surveyor 3 site. The 13‐meter crater has a sharp raised rim, and the 15‐meter crater has a more subdued rounded rim. The blocks associated with the subdued crater have twice as high a mean roundness as the blocks associated with the raised‐rim crater, and they are much more deeply buried. The size‐frequency distribution function for the fragments in each of the strewn fields of blocks resembles the size‐frequency distribution for fragments ejected by impacts in strong rock, such as Meteor Crater, Arizona. Most of the fragments at the surface of the Surveyor 3 landing site are evidently part of a layer of fragmental material of low cohesion that is at least 1 met...

The aureole of grooved terrain that surrounds the large shield volcano Olympus Mons consists of several overlapping roughly circular sheets, each 0.5 to 1.5 km thick. The surfaces of these materials bear abundant curvilinear ridges and troughs 10 to 100 km long and 1 to 5 km wide, which form anastomosing patterns that vary in length and width over the aureole. The aureole is asymmetric to Olympus Mons, extending almost 1000 km northwest from the center of the volcano but only 600 km southeast. The lobate form of the deposits, the pressure ridges on their surfaces, and the deflection of aureole material around barriers indicate that the deposits were emplaced as viscous flows. High‐resolution Viking orbiter pictures show the aureole material to be unstratified, and it is inferred to contain randomly distributed large dark blocks whose weathering products form dark streaks in the talus on the flanks of ridges. A pyroclastic origin is proposed for the aureole. The following sequence is suggested. At least six great pyroclastic eruptions occurred prior to the construction Olympus Mons, they formed very fluid ash flows that became viscous during late stages of emplacement, and pressure ridges formed on the surfaces of the deposits before they finally came to rest. The oldest and most extensive aureole deposit (finely grooved terrain) was considerably modified by erosion prior to being partly covered by later eruptions. A positive gravity anomaly over the Olympus Mons area may define the site of a near‐surface magma chamber that was the source of the pyroclastic eruptions.

Surveyor 7, the last spacecraft of the Surveyor series, landed about 30 km north of the rim crest of Tycho, one of the most prominent and well-known features in the southern part of the moon. About 21,000 pictures were transmitted during two lunar days of operation. At the Surveyor 7 site, the cumulative size-frequency distribution of craters 13 cm to 3 meters in diameter follows closely the distribution of craters observed at the other Surveyor sites in the lunar maria. This distribution of small craters is believed to be a steady-state distribution. The cumulative size-frequency distribution of craters 8 to 128 meters in diameter lies significantly below the steady-state distribution, however, and has a steeper slope. The upper limiting crater diameter for the steady-state distribution at the Surveyor 7 site is about 3 meters.On the basis of the crater distribution, the predicted median thickness of the regolith is 9 cm; the thickness of the regolith based on the depths to coherent material encountered by the surface sampler instrument is 2.5 to 15 cm.Rock fragments near Surveyor 7 range from less than i mm to several meters across. Fragments coarser than I mm in diameter occupy about 18% of the surface; fragments coarser than 10 cm in diameter occupy about 10% of the surface and are an order of magnitude more abundant than fragments of similar size at the Surveyor 6 landing site in Sinus Medii. The over-all particle size distribution must have at least two modes, one in the submillimeter range and one in the resolvable range. The rocks at the Surveyor 7 landing site exhibit a far greater variety of textural and structural characteristics than the rocks observed at any mare site. Some are plain, but other fragments are spotted. Some fragments appear to be massive, but others exhibit well-developed linear structures on their surfaces, which probably correspond to internal planar or linear structures. Most fragments appear to be relatively dense, but some are clearly vesicular. Some rocks scattered about Surveyor 7 exhibit one or more sets of intersecting linear ridges and grooves on their surfaces. The presence of intersecting sets of structures suggests that the fragments have been dynamically metamorphosed. The combined evidence of dynamic metamorphism and melting, observed in a number of fragments at the Surveyor 7 site, suggests these fragments have been shockmetamorphosed.The normal albedo of the undisturbed fine-grained material near the s?acecraft is 13.4%, whereas the rock fragments scattered over the surface have normal albedos ranging from 14 to 22%. Material ejected by the spacecraft footpads and excavated by the surface sampler has a normal albedo of 9.6%. The polarimetric properties of the fine-grained material near Surveyor 7 were found to be similar to those observed with the telescope for large parts of the lunar highlands. Various rock surfaces, however, exhibited much different. polarizing properties. Preliminary polarization measurements of the earth by Surveyor 7 indicate that the polarized c...