35th Meeting of the AAS Division on Dynamical Astronomy, April 2004
Session 6 Asteroids \& TNOs
Oral, Thursday, April 22, 2004, 2:15-6:50pm,

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[6.05] Yarkovsky-driven origin of the unstable population of asteroids in the 2:1 mean motion resonance with Jupiter

M. Broz, D. Vokrouhlicky (Charles Univ., Prague), A. Morbidelli (OCA, Nice), D. Nesvorny (SwRI, Boulder), F. Roig (IAG, Univ. de Sao Paulo, Sao Paulo)

The 2:1 mean motion resonance with Jupiter harbours a small population of asteroids; today, we know about 100 bodies with sizes between 2 and 30 km. Dynamical studies [1] allowed to classify these objects into three groups, namely those residing on stable, weakly unstable or highly unstable orbits (in comparison with the Solar System age). Their overall size distribution is much steeper (dN/N(>D) ~ D-4) than the size distribution of the adjacent, much larger population of main belt asteroids (with the cumulative slope -2.6). Moreover, differences in the size distribution are observed among the three dynamical classes of objects inside the 2:1 resonance - most importantly, the highly unstable population has a shallower slope -3.4 of the cumulative size distribution [1].

This may suggest (see also [2]), that the Yarkovsky effect can play a role in the transport of the asteroids from outside the 2:1 resonance onto the highly unstable orbits located inside this resonance. We investigate this scenario and consider three possible sources of asteroids: Themis family, Hygeia family and the background population. We use two different methods: (i) we determined orbital evolution paths and dynamical lifetimes of the asteroids pushed into the resonance by the Yarkovsky effect by direct N-body simulations, and (ii) a simpler semianalytic steady-state model was constructed to calculate the absolute number of expected resonant asteroids residing on the highly unstable orbits and their expected size distribution. The results of both approaches match very well properties of the highly unstable asteroid population in the 2:1 resonance, thereby suggesting our scenario for their origin is correct. On the other hand, stable and weakly unstable 2:1 populations cannot be explained by the Yarkovsky transport from the main belt and one needs a different mechanism to explain them.

[1] F. Roig et al. (2002) Mon. Not. R. Astron. Soc., 335(2), 417. [2] A. Morbidelli and D. Vokrouhlicky (2003) Icarus 163, 120.

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