The origin of long-lived asteroids in the 2:1 mean-motion resonance with Jupiter

• Published in: Monthly notices of the Royal Astronomical Society 2015-08, Vol.451 (3), p.2399-2416
• Main Authors: Chrenko, O., Brož, M., Nesvorný, D., Tsiganis, K., Skoulidou, D. K.
• Format: Article
• Language: English
• Subjects: Asteroids; Astronomy; Islands; Jupiter; Jupiter (planet); Mathematical models; Migration; Orbital resonances (celestial mechanics); Orbits; Origins; Physical properties; Planets
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stv1109

The 2:1 mean-motion resonance with Jupiter harbours two distinct groups of asteroids. The short-lived population is known to be a transient group sustained in steady state by the Yarkovsky semimajor axis drift. The long-lived asteroids, however, can exhibit dynamical lifetimes comparable to 4 Gyr. They reside near two isolated islands of the phase space denoted A and B, with an uneven population ratio B/A ≃ 10. The orbits of A-island asteroids are predominantly highly inclined, compared to island B. The size–frequency distribution is steep but the orbital distribution lacks any evidence of a collisional cluster. These observational constraints are somewhat puzzling and therefore the origin of the long-lived asteroids has not been explained so far. With the aim to provide a viable explanation, we first update the resonant population and revisit its physical properties. Using an N-body model with seven planets and the Yarkovsky effect included, we demonstrate that the dynamical depletion of island A is faster, in comparison with island B. Then we investigate (i) the survivability of primordial resonant asteroids and (ii) capture of the population during planetary migration, following a recently described scenario with an escaping fifth giant planet and a jumping-Jupiter instability. We also model the collisional evolution of the resonant population over past 4 Gyr. Our conclusion is that the long-lived group was created by resonant capture from a narrow part of hypothetical outer main-belt family during planetary migration. Primordial asteroids surviving the migration were probably not numerous enough to substantially contribute to the observed population.