03/dez/21 – The paths and fates of NEOS: dynamical evolution and lifetimes (M.Sc. Luana Liberato, GDOP/UNESP)

For many years, it was believed that the outer bodies from the main belt, centaurs and even TNOS that migrated inwards to the region of the terrestrial planets were, mostly, at the end of their lives and would end as a NEO. Within approximately 10 million years, these bodies would collide with the Sun, with some terrestrial planet or, in smaller portions, be ejected from the Solar System (SS) (Gladman et. al. 2000). But that does not seem to be accurate. Therefore we aim to study the dynamical evolution of the current known NEO population and review the half-life estimate for these bodies. Analyse their paths in the SS, their fates and the most common endings and behaviours of this population. We selected all NEOs with estimated diameters of at least 300 meters resulting in a sample of 5355 bodies. We did a series of 536 simulations, each consisting of all planets, the Sun and NEOs as test particles. We ran each simulation for up to 10^8 years, and the bodies were ejected from the SS once their orbits became hyperbolic. In this work, we find that the NEO population half-life is roughly 8.695 million years, which is consistent with the previous value using the same approach as Gladman et. al. (2000). However, if we count the lifetime of NEOs only when the bodies pericenters are inside Mars’ apocenter, then the half-life is considerably smaller, with approximately 4.2 million years. Only about 14% of the initial population never leaves the NEO region. For those who leave, only about 9% is resonant. The most common fate for NEOs is the ejection from the SS, corresponding to approximately 67% of the total, followed by 13.3% of collisions with the Sun, 10.8% of collisions with planets and only about 8.9% survived for 108 years. This large number of ejections lies in the fact that the most usual path for a NEO is to enter in the a x e space of the Jupiter family comets (JFC), and being highly affected by Jupiter it is ejected. Almost 52% of our sample takes that path directly from the NEO region, and 14.8% after becoming a main-belt object (MBO) for a while. At the same time, becoming JFC is the most likely route for the bodies that collide with the Sun, followed by those that become MBO first. And finally, the most probable way to collide with planets or to survive for 10^8 years is never leaving the NEO region.