Binary asteroids in mean-motion resonances

TL;DR

The study investigates whether binary asteroids preferentially occupy mean-motion resonances (MMRs) by analyzing over 700 objects from the Johnston Archive and Gaia DR3 binary candidates with a resonance-identification algorithm that includes planetary perturbations. Using 100 kyr integrations (10 Myr for TNOs) and classifications into libration or transition, the authors identify 82 newly resonant binaries across dynamical classes, with trans-Neptunian objects showing the highest resonant fraction (~30%) and main-belt binaries around ~11%. The results suggest resonances may contribute to both the formation and long-term survival of binary systems, particularly in the TNO region, while NEA populations exhibit elevated yet predominantly transient resonances. Overall, binary asteroids show a higher incidence of resonances than the general asteroid population, highlighting resonances as a potential driver of binary evolution and prompting further, longer-timescale studies and expanded catalogs.

Abstract

The purpose of this study is to investigate the relation between binary asteroids and mean motion resonances (MMRs). For more than 700 asteroids from two catalogues, the Johnston Archive [Johnston, 2024] and the Gaia DR3 VizieR list of binary candidates from Liberato et al. [2024], we applied a resonance identification algorithm, treating all planetary perturbations. Our results showed that the presence of binary asteroids in MMRs largely depends on their dynamical class. The highest percentage, more than 30%, is found in the Trans- Neptunian region, where most of these objects have exhibited resonant librations longer than 10 Myr. For the main-belt asteroid pairs, this percentage is about 10-12%. Contrary to expectations, the more unstable region populated with NEOs, showed a higher percentage of resonant pairs (above 17%), but with temporal resonant captures. These results could indicate that the mean motion resonances, particularly the stronger ones, could play a role in the evolution and formation of binary systems. Finally, we highlight that in the present paper, 82 resonant binary asteroids are newly identified.

Figures (2)

• Figure 1: The left plot illustrates the case of pure libration of the asteroid 119067 in the 4N-7 MMR with Neptune. The first two rows show that the resonant angle $\sigma$ and its filtered value $\sigma_f$ librate during the whole interval of 100 Kyr, while $a$ oscillates with the same frequency (row 3). The two periodograms (rows 4 and 5) indicate that the dominant period for both $\sigma$ and $a$ aligns at approximately 16,000 years. The last row displays the change in eccentricity with approximately the same period. The right panel shows the so-called transition status for the asteroid 20037 in the 8M-11 MMR with Mars. The asteroid is trapped in the resonance in several episodes between $t= \{[14,24], [28,42], [48,60], [63,98] \}$ Kyr when $\sigma$ and $\sigma_f$ (rows 1 and 2) librate, and $a$ oscillates with somewhat larger amplitudes (row 3). The two periodograms (rows 4 and 5) show a dense period distribution for times less than 5000 years, with the most dominant peaks at 2 kyr, 2.5 Kyr, and 3 Kyr. The eccentricity of the asteroid (row 6) illustrates a periodic change, but also a slight average increase in the first 50 Kyr.
• Figure 2: Binary resonant (red triangles), binary non-resonant (green triangles), and non-binary numbered (grey dots) asteroids in the TNO region. The vertical dashed lines mark the positions of semi-major axes for the most dominant MMRs in the region. The largest concentration of resonant binaries is found in the most populated TNO region between 44 and 45 AU, and in the most populated 2N-3 MMR in the region.