Venus: Crater distributions at low northern latitudes and in the Southern Hemisphere from new Arecibo observations

Abstract

Arecibo high resolution radar data covering approximately 23% of the surface of Venus was analyzed for circular features with crater‐like appearances. Overlapping Venera 15/16 radar data, with its more normal to the surface viewing geometry, was used to verity crater diameters measured from the Arecibo data. A comparison of the diameter‐frequency distribution of the possible impact features in the Arecibo data for northern latitudes south of 40°N and for the southern hemisphere with the distribution from the Venera 15/16 data for the northernmost quarter of the planet indicated similar distributions for large crater‐like features with diameters > approximately 30 km, but a deficiency of smaller craters in the Arecibo data. The average crater density measured for all craters in the northernmost quarter of the planet from the Venera 15/16 data was 1.27 per 106 km2 while the average for the 106 ×l06km2 covered by the Arecibo data was 0.95 per 106 km2. For craters with diameters less than 22km, the densities were 0.59 per million square kilometers for the Venera data compared with 0.33 per 106 km2 for the average of the two Arecibo data regions. All circular features in the Arecibo data with a crater‐like appearance that could not be excluded as being impact features were used in this study so the result represents an upper limit on the crater densities in the size interval considered. One possible process responsible for the density differences of small craters is a difference in the rate of volcanic resurfacing. An increase in the resurfacing rate of approximately 50% would explain the lower density of small craters in the area covered by the Arecibo data compared with the Venera data, but would not account for the differences being confined to the < 30 km crater diameter range.