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On the Dynamical Evolution and Lifetime of NEAs

Presentation #107.02 in the session “Asteroid Dynamics: Spinning, Tumbling, Running in Circles”.

Published onOct 03, 2021
On the Dynamical Evolution and Lifetime of NEAs

Many studies show that the NEOs (Near Earth Objects) are bodies from outer regions that migrated inwards. Before, they might have been TNOs, centaurs, main-belt objects (MBO), even comets from the edges of the Solar System. Whenever they become a NEO, they have an estimated lifetime of 10 Myrs and then collide with some planet, hit the Sun or get ejected from the Solar System. These aspects mislead to think that the Solar System’s minor bodies might be at the end of their lives once they reach the NEA region. Nevertheless, that is only part of the history. Gladman et al. (2000) estimated that NEAs have a half-life (or median life) of 10 Myr. In their work, were selected 117 asteroids, with pericenter q <1.3 au. They integrated the orbits for 60 Myr. The asteroids were removed from the integration if they collided with a large body (a planet or the Sun) or if they were ejected from the Solar System. More than half of the sample was eliminated by Sun-grazing process, which means that the asteroid’s pericenter was smaller than the solar radius. In the current work, we readdress this system considering 5355 NEAs with diameter > 300 m. The goal of our study is to analyze their dynamical evolution, paths, fates and lifetimes. We performed simulations for up to 100 Myr. The asteroids were only eliminated from the simulation once they collided with a planet or the Sun, or if their orbits became hyperbolic. Our results show that ~13% of the bodies hit the Sun, ~11% collide with some planet, and only ~9% of them survive for 100 Myr. Meanwhile, the vast majority of bodies end up ejected from the Solar System. The half-life of the studied NEA population was ~8.7 Myr. That measurement includes many bodies that were not ejected from the Solar System, but stayed far away from the NEA region earlier. Considering as lifetime only the period in which the body still had not left the NEA region (pericenter <1.666 au), we found the half-life estimate is only ~4.1 Myr. Tracking the fates of the initial NEA population, we found that ~1/3 of it will end its life as a different class of minor body (MBO, JFC, and Centaur). An estimation of the most common paths among the classes will be presented.

Acknowledgments: This work was funded by Fapesp (proc. 2016/24561-0), CNPq (proc. 305210/2018-1) and CAPES - Financing Code 001.

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