ABSTRACT: Impact Craters on Venus: A Pristine and Young Population

SCHABER, GERALD G., U.S. Geological Survey, Flagstaff, AZ

Impact craters on Venus are unique in the solar system because (1) they exhibit unusually pristine morphologies, (2) their size-frequency distributions are remarkably uniform from area to area across the entire planet, (3) craters larger than 35 km in diameter have unusually low densities, and (4) craters smaller than 35 km have densities that decrease rapidly with decreasing diameter. A total of 817 impact craters have been found on 89% of Venus's surface. Crater diameters range from about 2 km to 275 km. The crater data provide a basis for interpreting the age of the Venusian surface, geologic processes on Venus, and the effect of the dense atmosphere on impact cratering.

The degrees and styles of degradation of impact craters on Venus are unlike those on other planets. Sixty-three percent of the known craters are pristine, 33% are modified by fractures, and only 4% are embayed by lavas. Recent tectonic activity is implied by the fractured craters, which occur primarily in broad zones of topographic complexity in the Equatorial Highlands and northern latitudes. Pervasive resurfacing of the Venusian surface declined about 0.5 +/- 0.3 billion years ago, as indicated by crater density and estimated impacting rates of observed Venus-crossing asteroids. A rapid decline in volcanism accompanied the decline in resurfacing, as demonstrated by the small number and lack of variety of embayed craters. Study of Venus's crater population--because it is pristine--sh uld help us decipher Earth's much more complex cratering record.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)