Densities of Solar System Objects from Their Rotational Lightcurves

We present models of the shapes of four Kuiper belt objects (KBOs) and Jovian Trojan (624) Hektor as ellipsoidal figures of equilibrium and Roche binaries. Our simulations select those figures of equilibrium whose lightcurves best match the measured rotational data. The best fit shapes, combined with the knowledge of the spin period of the objects provide estimates of the bulk densities of these objects. We find that the lightcurves of KBOs (20000) Varuna and 2003EL61 are well matched by Jacobi triaxial ellipsoid models with bulk densities 992 −15 kgm −3 and 2551 −10 kgm , respectively. The lightcurves of (624) Hektor and KBO 2001 QG298 are well-described by Roche contact binary models with densities 2480 −80 kgm −3 and 590 −47 kgm , respectively. The nature of 2000GN171 remains unclear: Roche binary and Jacobi ellipsoid fits to this KBO are equivalent, but predict different densities, ∼2000 kgm and ∼650 kgm , respectively. Our density estimates suggest a trend of increasing density with size. Subject headings: Kuiper Belt objects — minor planets, asteroids — solar system: general