Triplicity and Physical Characteristics of Asteroid (216) Kleopatra

TL;DR

This study used high-resolution adaptive optics imaging, spectroscopy, and occultations to analyze asteroid (216) Kleopatra, revealing its shape, satellites, mass, density, porosity, and rotational characteristics, confirming its dog-bone shape and rubble-pile structure.

Contribution

First detailed high-resolution imaging and orbital analysis of Kleopatra's satellites, confirming its shape, mass, and physical properties with unprecedented precision.

Findings

Kleopatra has a dog-bone shape confirmed by AO imaging.

The asteroid's bulk density is approximately 3.6 g/cm³.

Kleopatra's physical characteristics suggest a rubble-pile structure with 30-50% porosity.

Abstract

To take full advantage of the September 2008 opposition passage of the M-type asteroid (216) Kleopatra, we have used near-infrared adaptive optics (AO) imaging with the W.M. Keck II telescope to capture unprecedented high resolution images of this unusual asteroid. Our AO observations with the W.M. Keck II telescope, combined with Spitzer/IRS spectroscopic observations and past stellar occultations, confirm the value of its IRAS radiometric radius of 67.5 km as well as its dog-bone shape suggested by earlier radar observations. Our Keck AO observations revealed the presence of two small satellites in orbit about Kleopatra (see Marchis et al., 2008). Accurate measurements of the satellite orbits over a full month enabled us to determine the total mass of the system to be 4.64+/-0.02 10^18 Kg. This translates into a bulk density of 3.6 +/-0.4 g/cm3, which implies a macroscopic porosity for Kleopatra of ~ 30-50%, typical of a rubble-pile asteroid. From these physical characteristics we measured its specific angular momentum, very close to that of a spinning equilibrium dumbbell.