Trapping and dynamical evolution of interplanetary dust particles in Earth's quasi-satellite resonance

We used numerical simulations to model the orbital evolution of interplanetary dust particles (IDPs) evolving inward past Earth's orbit under the influence of radiation pressure, Poynting-Robertson light drag (PR drag), solar wind drag, and gravitational perturbations from the planets. A series of beta values (where beta is the ratio of the force from radiation pressure to that of central gravity) were used ranging from 0.0025 up to 0.02. Assuming a composition consistent with astronomical silicate and a particle density of 2.5 g cm(-3) these beta values correspond to dust particle diameters ranging from 200 pm down to 25 mu m. As the dust particle orbits decay past 1 AU between 4% (for beta = 0.02, or 25 mu m) and 40% (for beta = 0.0025, or 200 mu m) of the population became trapped in 1:1 co-orbital resonance with Earth. In addition to traditional horseshoe type co-orbitals, we found about a quarter of the co-orbital IDPs became trapped as so-called quasi-satellites. Quasi-satellite IDPs always remain relatively near to Earth (within 0.1-0.3 AU, or 10-30 Hill radii, R-H) and undergo two close-encounters with Earth each year. While resonant perturbations from Earth halt the decay in semi-major axis of quasi-satellite IDPs their orbital eccentricities continue to decrease under the influence of PR drag and solar wind drag, forcing the IDPs onto more Earth-like orbits. This has dramatic consequences for the relative velocity and distance of closest approach between Earth and the quasi-satellite IDPs. After 10(4)-10(5) years in the quasi-satellite resonance dust particles are typically less than 10R(H) from Earth and consistently coming within about 3R(H). In the late stages of evolution, as the dust particles are escaping the 1:1 resonance, quasi-satellite IDPs can have deep close-encounters with Earth significantly below R-H. Removing the effects of Earth's gravitational acceleration reveals that encounter velocities (i.e., velocities "at infinity") between quasi-satellite IDPs and Earth during these close-encounters are just a few hundred meters per second or slower, well below the average values of 2-4 km s(-1) for non-resonant Earth-crossing IDPs with similar initial orbits. These low encounter velocities lead to a factor of 10-100 increase in Earth's gravitationally enhanced impact cross-section (sigma(grav)) for quasi-satellite IDPs compared to similar non-resonant IDPs. The enhancement in agrav between quasi-satellite IDPs and cometary Earth-crossing IDPs is even more pronounced, favoring accretion of quasi-satellite dust particles by a factor of 100-3000 over the cometary IDPs. This suggests that quasi-satellite dust particles may dominate the flux of large (25-200 mu m) IDPs entering Earth's atmosphere. Furthermore, because quasi-satellite trapping is known to be directly correlated with the host planet's orbital eccentricity the accretion of quasi-satellite dust likely ebbs and flows on 10(5) year time scales synchronized with Earth's orbital evolution. (C) 2013 Elsevier Inc. All rights reserved.