Main Belt Binary Asteroidal Systems With Circular Mutual Orbits

TL;DR

This study presents a detailed analysis of the mutual orbits of four main-belt binary asteroids, revealing predominantly circular orbits and providing insights into their densities and internal structures.

Contribution

It offers the first consistent orbital solutions for four main-belt binary systems and compares their characteristics, including densities and potential tidal evolution effects.

Findings

Mutual orbits are roughly circular.

Most systems have low bulk densities (~1 g/cm3).

Kalliope has a higher density (~3 g/cm3).

Abstract

In 2003, we initiated a long-term adaptive optics campaign to study the orbit of various main-belt asteroidal systems. Here we present a consistent solution for the mutual orbits of four binary systems: 22 Kalliope, 45 Eugenia, 107 Camilla and 762 Pulcova. With the exception of 45 Eugenia, we did not detect any additional satellites around these systems although we have the capability of detecting a loosely-bound fragment (located at 1/4 x RHill) that is ~40 times smaller in diameter than the primary. The common characteristic of these mutual orbits is that they are roughly circular. Three of these binary systems belong to a C-"group" taxonomic class. Our estimates of their bulk densities are consistently lower (~1 g/cm3) than their associated meteorite analogs, suggesting an interior porosity of 30-50% (taking CI-CO meteorites as analogs). 22 Kalliope, a W-type asteroid, has a significantly higher bulk density of ~3 g/cm3, derived based on IRAS radiometric size measurement. We compare the characteristics of these orbits in the light of tidal-effect evolution.