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Impact Craters of Venus with D>5 km Classified Based on Degree of Preservation of the Associated Radar-Dark Deposits

Introduction. This is a further continuation of work [1], which studied craters ≥30 km in diameter. That work used the approach of [2] to subdivide craters based on character of the associated radar dark deposits. It was suggested by [2] and then confirmed by [3] that the most pristine deposits of that sort are radar-dark parabolas. Non-parabolic radar-dark halos represent the next stage of the deposit evolution and then with time they disappear. So presence and character of crater-associated dark deposit can be used for estimates of the crater age and then for dating other features. Previous work [1] classified craters into: 1) craters with dark parabola (DP), 2) with clear dark halo (CH), 3) with faint halo (FH) and 4) with no dark halo (NH). It was found that abundances of craters superposed on regional plains (whose mean age is close to the planet mean surface age T) and belonging to DP, CH, FH and NH classes were correspondingly 15, 30, 30 and 25%. From that it was concluded that DP craters are not older than 0.1-0.15T; CH craters formed during the time interval from ~0.5T until 0.1-0.15T ago, and the FH and NH craters formed prior to ~0.5T ago (see details in [1]). It was shown that the DP, CH, FH and NH percentages show only slight apparent dependence on the crater geographic latitudes and no noticeable dependence on the crater size. The present study analyzes a much larger population (all D≥5 km craters) to investigate better the latitude effect and to study if within this larger crater population the size effect exists. First results of this extended approach were presented in [4]. The data analyzed. All craters ≥5 km in diameter imaged on the Magellan C1-MIDRPs and listed in database [5] were classified into DP, CH, FH and NH classes (Fig. 1).