How Are Diamond-Shaped Asteroids Sculpted

Abstract:

Rapidly spinning and loosely aggregated rubble-pile asteroids appear to take on diamond-shaped profiles, with elevated poles as well as equators. We derive an analytic expression for the shapes of such rapidly spinning rubble piles based on the principle that as rubble is deposited it assumes a critical angle of repose at which forces exactly balance. We show that this expression correctly reproduces diamond shapes, in accord with observations. We also use particle-based simulations to show that the characteristic diamond shape results from the redistribution of deposited debris guided by centrifugal forces. Our results imply that the shapes of such asteroids were produced during their early evolution, and were not a result of later reshaping.