VENUSIAN EJECTA PARABOLAS - COMPARING THEORY WITH OBSERVATIONS

The Magellan radar imager detected approximately 60 dark (i.e., low ba ckscatter cross section) parabola-shaped features on the surface of Ve nus; each parabola is oriented with the open end toward the west and e nvelops an impact crater near its ''focus.'' In this paper, we use a m odel of parabola formation to fit the 58 venusian parabolas observed t o date, as well as 9 circular features that are similar to the parabol as; we achieve good results for similar to 65% of the 41 parabolas tha t meet the conditions for the model to apply. As a result of modeling the parabolas, we derive a quantitative description of the distributio n of small(similar to 1 cm to similar to 1 mu m in diameter) impact ej ecta over a planetary surface. Our results agree well with the distrib ution of fine impact ejecta derived for the Terrestrial impact crater Chicxulub. In addition, our results lead to a method for estimating th e quantity of fine-grained material available on Venus for surface tra nsport processes such as saltation. (C) 1998 Academic Press.