JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 89, NO. B5, PAGES 3381-3399, MAY 10, 1984 Venus' The Nature of the Surface from Venera Panoramas JAMES B. GARVIN, JAMES W. HEAD, MARIA T. ZUBER, AND PAUL HELFENSTEIN Department of Geological Sciences, Brown University Images of the surfaceof Venus obtained by the Soviet Venera 9, 10, 13, and 14 landers have been analyzed to providea basis for understanding the nature of geologic processes operating there.The four spacecraft landed in the Beta-Phoebe region at median elevations in the upland rolling plains province. The landing points are each separated by distances of more than a thousandkilometers. The Venera panoramaswere digitized and transformed into various perspectives in order to facilitate analysisand comparison with other planetarysurfaces. Bedrock is exposed at the Venera 10, 13, and 14 sites and is characterized by semicontinuous, flat polygonal to subrounded patchesup to severalmeters in width. The bedrock surface is often dominated by subhorizontal to horizontal layered plates with thicknesses of several centimeters and abundant linear and polygonal verticai fractui'es. Angular to subangular layered to platy blocks in the5- to 70-cm range dominate theVenera 9 site andoccur much less frequently at the other sites. Blocks appear to sharemany characteristics with the exposed bedrockand are interpreted to belargely derived fromit. Soils (particles < 1 cm) areabundant at theVenera 9, 10, and 13sites but are uncommon at Venera 14.Features indicative of a strong eolian influence (moats, dunes, windtails) are not observed. A striking aspect of the Venera landing sites is their extremesimilarity despite separation distances of thousands of kilometers. Several hypotheses are considered for the origin of the bedrock surfaces, and we investigate in detail the hypothesis that bedrock originated from surface lava flows. In this interpretation, the broadlyplaty nature of the surface is analogous to the rolling and undulating natureof terrestrial pahoehoe flowscaused by the formation and deformation of a semisolid crust. The layeringis interpretedto be formed by a combinationof upper thermal boundary layer formation and horizontal sheets formed by cooling and sheafing during flow emplacement. Vertical fractures are at- tributed largely to joint patterns formed during cooling. Thisinterpretation made on thebasis of surface morphologyis consistent with Venera 13 and 14 geochemical resultswhich reported high potassium basaltand tholeiiticbasaltcompositions, respectively. If this interpretation is correct, large regions of the Beta-Phoebe area are likely to be characterized by lava flows.The relativefreshness of features observed by Venera 14 suggests that some bedrock surfaces are geologically youngor that erosion rates are low. 1. INTRODUCTION Imagesobtained by landedspacecraft and astronauts on the moon [-Surveyor Investigation Team, 1969; Vinegrader, 1971; USSR Academyof Sciences, 1966, 1969; Swannet al., 1972; Muehlberger et al., 1972], Mars [Mutch et al., 1976a,b; Garyin et al., 1981a, hi, and Venus [Florensky et al., 1977a, b, 1982a, b] have provided fundamentalinformation about planetary surfaces at scales from milllimeters to decameters. This infor- mation providesa meansof (1) documenting the types of geo- logic materials on the surface, (2) understanding the geologic processes operatingto form and modify planetary surfaces, (3) clarifying the nature of geologicfeaturesand processes inter- preted from orbital spacecraft imagesobtained at lower reso- lution, and (4) establishing a physical basis for the understand- ing of the behavior of incident electromagnetic radiation (e.g., radar) utilized in remote sensing of planetary surfaces. The purposeof this paper is to analyze the information collected by theSoviet Venera 9, 10,13, and14lander spacecraft imag- ing systems in order to allow a systematic comparisonwith other planetary surfaces and to provide an improved under- standing of the surface of Venus.Plate 1 displays the locations of the Venerasites on a map of the topography of the Beta- Phoeberegion on Venus.Table 1 summarizes details of the Venera lander missions. In order to facilitate morphologicand morphometricanalysis of surface features, the Venera images were transformedinto various perspectives, including those utilized in the analysis of the martian surface by the Viking landers [Garvin et al., 1983a]. The array of images is described in terms of three basic characteristics: bedrock,fragments, and Copyright 1984by the AmericanGeophysical Union. Paper number 4B0162. 0148-0227/84/004 B-0162505.00 soil.Comparisons are thenmade with the surfaces of the moon• earth, and Mars to provide a basisfor the interpreta- tion of the surface of Venus. 2. IMAGING SYSTEMS AND TRANSFORMATION METHODS The cameras aboard the Venera spacecraft were digital fac- similescanning telephotometers [Florensky e t al., 1977b; Keldysli, 1979; Moro•, 1983; Bokshteyn et al., 1983]. The cam- eraswere locatedabout 90 cm abovethe baseof the spacecraft and werepointed 50 ø downward from the horizontal planeof the spacecraft. The imaging system scans in verticalsweeps of 40 ø and views 90 ø to the left and right of the subcamera point on the surface in front of the spacecraft. The camera rotates about a fixedaxisproducing an inclined cylindrical projection. This particular camera orientation wasused in order to allow boththe near-field and the far horizon to be imaged using a single, fixed viewing geometry. This viewing geo.rnet•y results in the apparentlyinclined horizon visible at the far left and right of the unrectified panoramas (Figures 1-3). Objectsin the near field directly in front of the lander impact ring are relatively undistorted, whileobjects nearest the horizon are stretched bya factor of2-3 in the horizontal direction. Vener- as 9 andi0 were each equipped withcameras on one side of the spacecraft, whileVeneras 13 and 14 were each equipped with two similar imaging •systems, located 180 ø apart. For Veneras 13 and 14 the 180 ø azimuthal COverage for each camerasystem allowed small regions of overlap in the lower corners of the panoramas so that, whenrectified, a continuous 360 ø view ofa narrow portion ofthe surface ofVenus can • produced. Veneras 9 and 10 obtained black andwhite images only, while Veneras13 and 14 obtained black and white and color images •Florensky et al., 1982a,hi. The dimensions of various spacecraft partsare listed for scale in Table 2. 3381