A region‐by‐region condensed description of almost all of the area that was radar‐photographed by Veneras 15 and 16 is presented. Using some generalizations, the diversity of terrain was reduced to a discrete set from which a geological‐morphological map was constructed. The predominant type of terrain of the studied area is a plain that was tentatively subdivided into five morphological types: ridge‐and‐band, patchy rolling plain, dome‐and‐butte plain, smooth plain, and high smooth plain. Stratigraphically, the ridge‐and‐band plains are the oldest and the smooth plains are the youngest. The stratigraphic position of the other types is yet to be determined. Large sections of the plains show similarities to the mare‐type basaltic plains of the moon, Mercury, and Mars. Other types of terrain are combinations of ridges and grooves in various patterns: linear parallel, orthogonal, diagonal or chevron‐like, and chaotic. In some places the ridge‐and‐groove terrain is Stratigraphically below the plain material, but in other places it appears to be plain material that has been subsequently deformed. Near the eastern and western boundaries of Ishtar Terra large (several hundred kilometers in diameter) ring‐like features can be seen that are named coronae or ovoids. Evidence of tectonic deformation and the presence of flow‐like patterns support their designation as volcano‐tectonic features. Beta Regio seems to be an uplifted plain showing evidence of rifting and volcanism. All types of terrain are sparesely peppered with craters of obvious impact morphology. Their average density gives the plain an age range of 0.5 to 1×109 years. The fact that many impact craters are still in the pristine state indicates a very low rate of surface reworking, at least for the last 0.5 to 1×109 years. No evidence for water‐erosion‐sedimentation processes has been found. The tectonic activity of Venus has no equivalent on the moon, Mercury, or even Mars, and can be compared only with that of the Earth. Intensive horizontal deformation, previously known only on Earth, occurs on Venus, but in a characteristic Venusian style.

Before the Magellan mission, the best estimates of the rotation rate and pole direction of Venus were derived from Earth‐based radar measurements. A new determination of these rotational parameters has now been made from an analysis of Magellan radar images. Control points were selected from the north polar region and measured on full‐resolution radar strips. The measurements were entered into a least squares adjustment to solve for the pole direction and rotation rate of Venus, as well as the coordinates of the control points themselves. The current data set contains 3893 measurements of 571 points on 560 radar strips. Spacecraft ephemeris errors dominate the measurement errors. One technique used to remove ephemeris errors is to adjust the averaged orbital inclination and argument of periapsis for each orbit. In a more precise technique used for selected blocks of orbits, an improved spacecraft ephemeris is computed by optimally fitting measurements of additional points at all latitudes of the radar strips together with Earth‐based spacecraft radiometric tracking measurements. In a separate experiment, measurements were made of a few points common to both Venera 15/16 and Magellan images. The long time baseline between the images should have led to an accurate determination of the rotation period and pole direction of Venus. However, the measurement residuals were unexpectedly large, and these solutions are not currently considered reliable. A rotation period estimate of 243.0185 ± 0.0001 days was determined via the ephemeris improvement technique applied simultaneously to two overlapping orbit blocks with many common points and separated by two full Venus rotations. Using this period value, the control network computations estimated the north pole direction as right ascenson = 272.76° ± 0.02° and declination = 67.16° ± 0.01° in the J2000 frame.

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A global array of 20 radio observatories was used to measure the three-dimensional position and velocity of the two meteorological balloons that were injected into the equatorial region of the Venus atmosphere near Venus midnight by the VEGA spacecraft on 11 and 15 June 1985. Initial analysis of only radial velocities indicates that each balloon was blown westward about 11,500 kilometers (8,000 kilometers on the night side) by zonal winds with a mean speed of about 70 meters per second. Excursions of the data from a model of constant zonal velocity were generally less than 3 meters per second; however, a much larger variation was evident near the end of the flight of the second balloon. Consistent systematic trends in the residuals for both balloons indicate the possibility of a solar-fixed atmospheric feature. Rapid variations in balloon velocity were often detected within a single transmission (330 seconds); however, they may represent not only atmospheric motions but also self-induced aerodynamic motions of the balloon.

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