INTRODUCING THE GAUSSIAN SHAPE HYPOTHESIS FOR ASTEROIDS AND COMETS

A hypothesis is presented that the irregular shapes of asteroids and c ometary nuclei can be modeled by using lognormal statistics (Gaussian random sphere). The Gaussian sphere is fully described by the mean and covariance function of the radius. A suitable covariance function is devised here for the generation of sample Gaussian spheres that closel y resemble the shapes observed for asteroids. To collect more evidence for the Gaussian hypothesis, assuming simple Lommel-Seeliger and Lamb ert scattering laws, lightcurves are computed for rotating Gaussian sp heres. The results show striking similarities to asteroid lightcurves. For example, the observed increase of lightcurve amplitude with incre asing solar phase angle appears to be at least partly explained by the numerical simulations. Making further use of the Gaussian random sphe re, a statistical model is developed for albedo variegations on astero ids, and for characterizing active regions on cometary nuclei.