WIND INTERACTION WITH FALLING EJECTA - ORIGIN OF THE PARABOLIC FEATURES ON VENUS

Unusual parabolic features associated with impact craters have been ob served by Magellan on Venus. A strong correlation exists between the o rientation of the features and the zonal winds on Venus. We propose a quantitative model in which the parabolic features are produced by the interaction of the zonal winds with material ejected ballistically fr om the impact crater. As the ejecta particles fall through the atmosph ere, the winds transport them downwind from their entry point, smaller particles being transported a greater distance. Since the ejecta dist ribution is initially axially symmetric and smaller particles are thro wn farther from the crater, the winds blow the particles on the upwind side back upon one another, leading to a pile-up of material. On the downwind side, the winds disperse the ejecta particles and no pile-up occurs. The resulting thickness distribution on the Venusian surface m atches the observed parabolic features closely. The dual parabolic fea ture associated with the crater Carson is also explained by this model .