Asteroid families in the first order resonances with Jupiter (1104.4004v1)

Abstract: Asteroids residing in the first-order mean motion resonances with Jupiter hold important information about the processes that set the final architecture of giant planets. Here we revise current populations of objects in the J2/1 (Hecuba-gap group), J3/2 (Hilda group) and J4/3 (Thule group) resonances. The number of multi-opposition asteroids found is 274 for J2/1, 1197 for J3/2 and 3 for J4/3. Using both hierarchical clustering technique and colour identification we characterise a collisionally-born asteroid family around the object (1911) Schubart in the J3/2 resonance. There is also a looser cluster around the largest asteroid (153) Hilda. Using N-body numerical simulations we prove that the Yarkovsky effect (infrared thermal emission from the surface of asteroids) causes a systematic drift in eccentricity for resonant asteroids, while their semimajor axis is almost fixed due to the strong coupling with Jupiter. This is a different mechanism from main belt families, where the Yarkovsky drift affects basically the semimajor axis. We use the eccentricity evolution to determine the following ages: (1.7+-0.7) Gyr for the Schubart family and >~4 Gyr for the Hilda family. We also find that collisionally-born clusters in the J2/1 resonance would efficiently dynamically disperse. The steep size distribution of the stable population inside this resonance could thus make sense if most of these bodies are fragments from an event older than ~1 Gyr. Finally, we test stability of resonant populations during Jupiter's and Saturn's crossing of their mutual mean motion resonances. In particular we find primordial objects in the J3/2 resonance were efficiently removed from their orbits when Jupiter and Saturn crossed their 1:2 mean motion resonance.

Asteroid Families in First Order Resonances with Jupiter

The paper of asteroid populations within the Jovian first-order mean motion resonances provides insight into the dynamical evolution of both these small bodies and the giant planets themselves. This paper, authored by M. Brož and D. Vokrouhlický, revises the analysis of asteroid families located in the J2/1 (Hecuba-gap group), J3/2 (Hilda group), and J4/3 (Thule group) resonances with Jupiter.

The authors have identified 274 multi-opposition asteroids in the J2/1 resonance, 1197 in the J3/2, and 3 in the J4/3. Notably, the inclusion of (186024) 2001 QG207 and (185290) 2006 UB219 in the Thule group confirms it as a genuine group rather than an outlier. Using a combination of hierarchical clustering and color identification, the paper characterizes the collisional Schubart family among the Hilda group and indicates the existence of a looser cluster around (153) Hilda.

One key investigation involves the Yarkovsky effect, which induces a drift in eccentricity for resonant asteroids while maintaining a near-constant semimajor axis due to the strong gravitational influence of Jupiter. This contrasts with the primary belt families, where the Yarkovsky effect mainly shifts the semimajor axis. The paper estimates the ages of the Schubart family at approximately 1.7±0.7 Gyr, while the Hilda family is determined to be over 4 Gyr old. The researchers also find that collisionally-born clusters in the J2/1 resonance disperse efficiently, suggesting that the stable population's steep size distribution is consistent with fragmentation from an event older than roughly 1 Gyr.

The paper also addresses the stability of populations during the dynamical history of the giant planets. Essentially, the authors test the stability of asteroid families as Jupiter and Saturn crossed their mutual mean motion resonances. The findings suggest that primordial objects in the J3/2 resonance were effectively removed when these planets crossed the 1:2 mean motion resonance. The potential upheaval from planetary migration models like the Nice model significantly impacts resonant populations, resulting in rapid depletion or migration of primordial groups into these zones.

The implications extend to both practical and theoretical considerations, providing benchmarks for potential collisional origin and generating insights into the primordial configurations and stability of the early Solar System. The paper also lays groundwork for future computational and observational efforts, particularly the influence of smaller-size populations under resonant conditions and the role of non-gravitational forces such as YORP in further destabilizing resonant bodies. Moreover, this work underlines the necessity of high-precision models for planetary migration mechanisms to understand the broader architecture and evolution of our Solar System's structure.

The exploration of these asteroid families not only contributes to understanding the intricate dynamics within the Solar System but also aids in tracing the historical trajectory of planetesimal populations influenced by the ongoing evolution of the planetary orbits.