A dynamical study of the Gefion asteroid family

The Gefion asteroid family is a group of S-type asteroids located between the 8J:-3A and 5J:-2A mean-motion resonances. The 5J:-2A resonance seems to be responsible for the absence of the right side of the V-shape of this family. We aim in this work to present a detailed study on the Gefion family, motivated by the incompatibility found in previous family age estimations and the fact that this family could be seen as one of the most probable sources of L-chondrite meteorites. After eliminating all possible taxonomical and dynamical interlopers, we use a Monte Carlo method to analyze the semi-major axis evolution of several fictitious families under the influence of the Yarkovsky and Yarkovsky-O’Keefe-Radzievsky-Paddack (YORP) effects. We also perform simulations using symplectic integrators to account for the Yarkovsky effect (diurnal and seasonal versions) and the stochastic YORP effect. We make use of the distribution of the component of the ejection velocity field (vW) perpendicular to the orbital plane and the time dependence of the asymmetry of the distribution of the target function of a fictitious family generated with ejection velocity parameter $20^{+55}_{-15}$ m s−1 to obtain an age estimate of $1030^{+19}_{-67}$ Myr. We find that 6.5% of asteroids from the Gefion family can reach orbits similar to particles in the current near-Earth objects space; 73% of them are among the Amors asteroids, and the remaining ones are among the Apollos. We only found 0.5% from the Gefion family reaching the Mars-crossing space