Orbital mobility of asteroids in the Inner Main Belt: A closer look at gravitational diffusion

Gravitational (aka chaotic) diffusion (GD) that modifies the eccentricity and inclination of Main Belt asteroids independently of size is an important driver of gradual MB erosion and of delivery of MB material to near-Earth space. GD competes with Yarkovsky radiation forces causing semimajor axis drift for < 40 km asteroids and of meteorite-dropping fragments. With observational surveys continuing to improve our knowledge of the Belt, understanding the relative efficiency of these mechanisms is crucial to interpret the new observations and constrain its genealogy and evolution. Here we make a fresh appraisal of GD in the inner MB (2.1 < a < 2.5 au), using simulations of test particles with precisely-controlled initial orbits near the 1M-2A mean motion resonance. We find that the proper e and I of chaotically-diffusing asteroids follow a zero-mean gaussian distribution with a dispersion that grows as a power-law of time and a fixed exponent that is independent of starting location. We use our findings to show that (i) high-I asteroids are dynamically isolated from the rest of the IMB and from the observed asteroid families, and (ii) resonances facilitate exchange of material between neighbouring families.