While the number of asteroids with known shapes has drastically increased over the
past few years, little is known on the time-evolution of shapes and the underlying
physical processes. Here we propose an averaged abrasion model based on micro-collisions,
accounting for asteroids not necessarily evolving toward regular spheroids, rather
(depending on the fall-back rate of ejecta) following an alternative path, thus confirming
photometry-derived features, e.g., existence of large, relatively flat areas separated
by edges. We show that our model is realistic, since the bulk of the collisions falls
into this category.