On the Dynamic Evolution of the Population of Near-Earth Asteroids

Abstract

We consider some aspects of the dynamic evolution of the population of near-Earth asteroids (NEAs): the change of the rate of NEA depletion with time, including the dependence of the rate on the initial parameters of the NEA orbits, the efficiency of various channels of NEA depletion, and diffusion of NEA orbits. We studied both real asteroids and a simulated population. For the study, 3024 real asteroids larger than 1 km with a perihelion distance $q < 1.6$ A.U. were selected, of which 833 NEAs had $q < 1.3$, i.e., we explored almost all large NEAs. For some tasks, the population of NEAs was also modeled using NEOPOP (ESA) code. The orbits were integrated for 10 Myr using the REBOUND numerical complex. The solar gravitational field and field of planets, as well as the possibility of collisions, were considered. It is shown that the total population of NEAs has the median time of depletion ${{t}_{{{\text{NEA}}}}} \simeq 3.5$ Myr; this rectifies the estimates of other authors. The main advantage of the present study is that, for the first time, the dependence on the initial values ​​of the orbital parameters—semi-major axis of the orbit and eccentricity was investigated. It is shown that this dependence is very strong: for the subset of asteroids with large $a$ and $e$, ${{t}_{{{\text{NEA}}}}}$ it is dozens of times lower than for the subset with small $a$ and $e$. Obtained qualitative estimates of the dependence ${{t}_{{{\text{NEA}}}}}(a,\;e)$ are important for the quantitative analysis regarding the various model adequacy of mechanisms of replenishing the population of NEAs. The details of the diffusion (mixing of parameters) of the asteroid orbits in the plane “a–e” in the process of evolution have been studied. During the integration time, 10% of the NEAs were ejected from the Solar System, 1.5% fell onto the planets (including 0.2% onto the Earth), 17% fell onto the Sun, and 12.5% ​​left the NEAs zone.