Deficit of primitive compositions in binary asteroids and pairs

TL;DR

This study finds that binary asteroids and pairs predominantly have mafic-silicate rich compositions, with a notable deficit of primitive types, suggesting composition influences their formation via spin-up fission.

Contribution

It provides the first comparative analysis of taxonomic class distributions between binary asteroids, pairs, and the general asteroid population, highlighting composition's role in binary formation.

Findings

Primitive asteroid types are underrepresented in binary systems.

Mafic-silicate rich asteroids are more common among binaries.

Primitive compositions are less likely to form binary systems.

Abstract

Context. Small binary asteroid systems and pairs are thought to form through fission induced by spin up via the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. This process is expected to depend on their structural strength, hence composition. Aims. We aim to determine how taxonomic classes, used as a proxy for composition, distribute amongst binary asteroids and asteroid pairs compared to the general population. Methods. We compare the distribution of taxonomic classes of binary systems and pairs with that of a reference sample of asteroids. We build this sample by selecting asteroids to reproduce the orbital and size distribution of the binaries and pairs to minimize potential biases between samples. Results. A strong deficit of primitive compositions (C, B, P, D types) among binary asteroids and asteroid pairs is identified, as well as a strong excess of asteroids with mafic-silicate rich surface compositions (S, Q, V, A types). Conclusions. Amongst low mass, rapidly rotating asteroids, those with mafic-silicate rich compositions are more likely to form multiple asteroid systems than their primitive counterparts.