Dynamic evolution scale of NEA population: dependence on the initial orbital parameters.

The history of crater formation on the Moon idicates that the number of NEAs larger than 50 m practically did not change over the past 2–3 Gyr. On the other hand a dynamic scale of the NEA population, which could be characterized by the depletion time by half t NEA , is many orders of magnitude shorter. There are significant variations of t NEA estimates by other authors. It is important to know this value more precisely, since this knowledge imposes restrictions on the mechanisms of replenishment of the NEAs, the lifetime of the Main Asteroid Belt, etc. In the Zolotarev & Shustov (2021) we have estimated t NEA as 3.5 million years. We noted either that t NEA for subgroups of NEAs depends on the initial orbital parameters of the subgroups. In the current study we considered this dependence quantitively. We have integrated orbits of 10 000 asteroids larger than 1 km and q <1.72 AU over 20 Myr. These sample essentially includes all large NEAs (>1km). The NEA subsample is considered to be complete. We made integrations with the REBOUND software package using the MERCURIUS hybrid scheme (Rein et al. (2019)). To reveal dependence of t NEA on orbital parameters t NEA (a, e, i) we divided the NEA subsample into 18 subgroups according to their orbital parameters. We found that t NEA is substantially higher for subgroups with higher i and e. There is strong dependence of t NEA on a. All these dependencies are explained by a different number of close approaches of asteroids from NEA subgroups to planets. We found that depletion of total NEO population can be approximated remarkably well with the following expression: N(t)/N 0 = exp (−0.5× t 0.33)where N 0 is an initial number and N(t) – a current number of NEAs. [ABSTRACT FROM AUTHOR]