Draft version June 6, 2018 Preprint typeset using L A T E X style emulateapj v. 11/10/09 THE OBSERVED ORBITAL PROPERTIES OF BINARY MINOR PLANETS Smadar Naoz $^{1}$,$^{2}$, Hagai B. Perets3 and Darin Ragozzine 3 Draft version June 6, 2018 Abstract Many binary minor planets (BMPs; both binary asteroids and binary Trans-Neptunians objects; TNOs) are known to exist in the Solar system. The currently observed orbital and physical properties of BMPs hold essential information and clues about their origin, their evolution and the conditions under-which they evolved. Here we study the orbital properties of BMPs with currently known mutual orbits We find that BMPs are typically highly inclined relative to their orbit around the sun, with a distribution consistent with an isotropic distribution. BMPs not affected by tidal forces are found to have high eccentricities with non-thermal eccentricity distribution peaking at intermediate eccentricities (typically 0 . 4 − 0 . 6 ). The high inclinations and eccentricities of the BMPs suggest that BMPs evolved in a dense collisional environment, in which gravitational encounters in addition to tidal and secular Kozai affects played an important role in their orbital evolution. The binary asteroids and binary Trans-Neptunian ob- jects (TNOs) discovered in recent years show a large diversity of orbital properties, showing a wide range of eccentricities, inclinations, separations and mass ratios. Many models have been suggested for the origin of these binary minor planets (BMPs) and their orbital configu- rations (Richardson & Walsh 2006). An essential com- ponent in constraining theoretical models for the origin and evolution of BMPs is understanding the distribu- tion of their orbital parameters. The number of BMPs with known orbital parameters is currently small. Nev- ertheless, 29 BMP systems already have full solutions for their mutual orbits, including 17 TNOs and 12 asteroids (we do not consider near earth objects which have much shorter lifetimes). We study the orbital properties of the 29 main belt and transneptunian binaries (which we re- fer to corporately as BMPs) to provide clues to and con- straints on their evolutionary history. Several reviews have presented the observed separations of BMPs (e.g. Richardson & Walsh 2006; Noll et al. 2008; Walsh 2009) here we focus on the distributions of eccentricities and inclinations, not shown before. In addition, we discuss the relations between the orbital parameters of BMPs, including their observed periods/separations. In the following we present and discuss the published orbital solutions of BMPs. We present the distributions of the orbital parameters of these BMPs, treating binary TNOs and binary asteroids separately. We also discuss the selection biases affecting both samples. We then briefly study the implications of our findings regarding the conditions in the early Solar system and the forma- tion and evolutionary scenarios of BMPs. There are significant observational selection effects present in the current distribution of binary TNOs and asteroids. These effects are very difficult to correct since they depend on several factors, and the currently ob- In some cases two degenerate orbital solutions were found for the BMPs; these solutions differ significantly in their derived inclinations, but have very similar ec- centricities. In these cases we detail both solutions (see table 1) and we use the published eccentricities to de- rive the eccentricity distribution (shown in Fig. 1). All published binary asteroids orbits have unique solution for the inclination (besides the binary asteroids Balam for which only the eccentricity is known) and we show their mutual inclination distribution (in cos i ; Fig. 2). Only 5 of the binary TNOs, however, have a unique non- degenerate solutions for their inclinations. We therefore can not show the true inclination distribution for binary TNOs with significant statistics (Fig. 2 shows the distri- bution of binary TNOs inclination for an arbitrary choice of one solution for each binary TNO from the two pos- sible degenerate solutions published). Nevertheless, we do consider all the possible distributions of the binary TNOs in a statistical manner (see section 3). Note that both binary TNO and binary asteroid populations are presented. Given that these two populations differed in the conditions under which they evolved, their orbital properties are presented separately. The mutual orbits of 30 BMPs have been published in the literature (see tables 1 and 2), some of them with two degenerate solutions, and a few published with no indicated inclination. Table 1 shows the physical prop- erties and orbital parameters of BMPs with known incli- nations in the solar system. In the literature the orbital parameters of BMPs are typically given with respect to the ecliptic plane, while the inner orbital parameters are given with respect to the equatorial frame of reference. For our analysis we are interested in the mutual inclina- tions between the BMP orbit around the Sun and the BMP inner orbit, therefore we used the published data to calculate these inclinations for our analysis of the dy- namical evolution (see Appendix). 1. INTRODUCTION 2. THE ORBITAL PARAMETERS OF BMPS 2.1. The data 2.2. Selection effects arXiv:1001.2558v2 [astro-ph.EP] 24 Jun 2010 1 CIERA, Northwestern University, Evanston, IL 60208, USA 2 Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel 3 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge MA 02138, USA