Earth-Based Radar Imagery of Venus

Observations with the 12.6-cm radar system at the Arecibo Observatory in 1975 and 1977 have yielded images covering approximately 25% of the surface. The resolutions of these images range from 5 to 20 km. Most of the apparent large features correlate to some degree with features in the Pioneer Venus altimetry data. The correlation is especially good for the continental-sized elevated region, Ishtar Terra, in the north and Beta Regio at 30 N latitude, for which a volcanic origin has been suggested. Over 30 circular features have been observed and tentatively identified as craters. Whether they are of volcanic or impact origin cannot be determined at the relatively poor resolution attained here. A comparison of their characteristics and statistics with those of known impact craters on the moon, Mercury, and Mars suggests that at least some of them may be of impact origin. Assuming that all of them are impact craters and that we have detected most of the larger ones with diameters above 100 km, the small number found indicates that Venus may have a relatively young surface.