Dumb-bell-shaped equilibrium figures for fiducial contact-binary asteroids and EKBOs

TL;DR

This paper explores the equilibrium shapes of dumb-bell-shaped models for contact binary asteroids and EKBOs, proposing a better fit for observed data and estimating their physical properties.

Contribution

It introduces a new class of dumb-bell-shaped equilibrium figures that improve modeling of contact binary asteroids and EKBOs, with applications to observed light curves and physical property estimation.

Findings

Dumb-bell shapes fit observed light curves of specific asteroids.

New estimates of bulk density and size for Kleopatra and Hektor.

Dumb-bell models outperform traditional Roche binary approximations.

Abstract

In this work, we investigate the equilibrium figures of a dumb-bell-shaped sequence with which we are still not well acquainted. Studies have shown that these elongated and nonconvex figures may realistically replace the classic "Roche binary approximation" for modeling putative peanut-shaped or contact binary asteroids. The best-fit dumb-bell shapes, combined with the known rotational period of the objects, provide estimates of the bulk density of these objects. This new class of mathematical figures has been successfully tested on the observed light curves of three noteworthy small bodies: main-belt asteroid 216 Kleopatra, Trojan asteroid 624 Hektor and Edgeworth-Kuiper-belt object 2001 QG298. Using the direct observations of Kleopatra and Hektor obtained with high spatial resolution techniques and fitting the size of the dumb-bell-shaped solutions, we derived new physical characteristics in terms of equivalent radius and bulk density. In particular, the growing inadequacy of the radar shape model for interpreting any type of observations of Kleopatra (light curves, AO images, stellar occultations) in a satisfactory manner suggests that Kleopatra is more likely to be a dumb-bell-shaped object than a "dog-bone".