Geology and distribution of impact craters on Venus: what are they telling us?

Abstract

Magellan has revealed an ensemble of impact craters on Venus that is unique in many important ways. A data base describes 842 craters on 89% of Venus' surface mapped through orbit 2578. The data indicate that the plant's cratering record was erased by a global resurfacing event or events, the latest ending about 0.5Ga, after which volcanic activity declined. Since the last resurfacing event, a maximum of 10% of the planet has been resurfaced and only about 4% of the craters have been obliterated. The data also confirm quantitatively the expectation that the dense atmosphere of Venus has strongly affected the production of craters. Large impactors have been relatively unaffected, intermediate-sized ones have been fragmented and have produced overlapping or multiple craters, a narrow size range has produced shock-induced "splotches' but no craters, and the smallest bodies have had no observable effect on the surface. The number of craters eliminated by the "atmospheric filter' is enormous. Unique crater-related features such as parabolas and outflow deposits demonstrate the roles of Venus' high atmospheric density and temperature in modifying the crater formation process. Finally, heavily fractured craters and lava-embayed craters are found to have higher than average densities along the major fracture belts and rifted uplands connecting Aphrodite Terra and Atla, Beta, Themis, and Phoebe regiones. -from Authors