Photometric signatures of highly nonconvex and binary asteroids

Abstract

We present an analysis of synthetic lightcurves of highly nonconvex single or synchronous binary asteroids, paying particular attention to the connection between the available solar phase angels and the observable degree of asteroid nonconvexity. The measure of nonconvexity of an object is defined and computed for asteroids with known shapes. We discuss the possibility of recovering global nonconvexities or binary structure of an asteroid from its lightcurves. The importance of observations at high solar phase angles is emphasized. For main-belt asteroids only binary or bifurcated shapes can be resolved (at least in a qualitative sense) - topologically star-like asteroids can be modelled as convex bodies. Concavities can be revealed only if an asteroid is observed at sufficiently high solar phase angles (α > 60°) when shadowing effects from nonconvexities become important. This can be fulfilled only for near-Earth asteroids. Reconstruction of local topographic details is in practice precluded by the uncertainty of the light-scattering properties of the surface and the scarcity of very large phase angles.