Warren B. Hamilton, Department of Geophysics, Colorado School of Mines, Golden, Colorado 80401, USA, firstname.lastname@example.org
Venus displays thousands of circular structures, typically rimmed depressions, with pristine to variably degraded or buried morphology of types expected for impact origins. The overwhelming consensus among Venusian specialists is that only the 1000 small pristine structures among these record impacts, all others being products of plumes and other hypothetical endogenic processes younger than 1 Ga. This consensus is based on a chain of questionable conjectures regarding planetary evolution, rather than on analysis of structures. There are all gradations from the pristine structures to the most deeply eroded or buried ones. Four of the best preserved of the pre-pristine circular structures are gigantic, with topographic rims 800-2000 km in diameter, and if indeed of impact origin must, by lunar analogy, be ~3.9 Ga. That Venus retains a landscape from late-stage planetary accretion accords with other information from the planet itself, but not with conventional interpretations of its geology and dynamics.
Figure 3. Variably preserved impact craters, numbered in order of increasing age. 1, pristine Cohn Crater. 2, Isabella Crater, second-largest pristine crater on planet, rimcrest diameter 175 km; apron of radial lobate debris flows; long runout to SE fluidized by water in target sediments? 3, deep crater, partly covered by debris from 2, 60 km rim (conventional endogenic Noti Corona). 4, tiny rim-only (but "pristine") Alimat Crater. 5, 6, and 7, rim diameters ~50 km each, ignored in conventional analysis. 8, endogenic Epona Corona of conventional interpretation.
Download complete paper as a PDF file, with Magellan radar imagery analysis
Two Related Papers
" An Alternative Earth " -- A radical new look at geodynamics past and present. Published in GSA Today, November 2003.
" Plumeless Venus has ancient impact-accretionary surface " -- A similarly radical view of Venus (a not-quite-final version of a paper to be published in mid 2005 in Geological Society of America Special Paper 388):