Assessing the physical nature of near-Earth asteroids through their dynamical histories

•Most NEAs with Q > 4.8 au are found to move on highly stable “asteroidal” orbits.•Most of these NEAs are found in MMR with Jupiter, in particular the 2:1.•The Kozai mechanism is responsible for driving many of these NEAs toward the Sun.•Yet a small fraction of them move on highly unstable “cometary” orbits (NEACOs).•If NEACOs are of comet origin, the fraction is only ∼0.14 among NEAs with Q > 4.8 au.

We analyze a sample of 139 near-Earth asteroids (NEAs), defined as those that reach perihelion distances q<1.3au, and that also fulfill the conditions of approaching or crossing Jupiter’s orbit (aphelion distances Q>4.8au), having Tisserand parameters 24.8au of cometary origin, but it could be even lower if the NEAs in unstable orbits listed before turn out to be bona fide asteroids from the main belt. This study strengthens the idea that NEAs and comets essentially are two distinct populations, and that periods of dormancy in comets must be rare. Most likely, active comets in near-Earth orbits go through a continuous erosion process in successive perihelion passages until disintegration into meteoritic dust and fragments of different sizes. In this scenario, 289P/Blanpain might be a near-devolatized fragment from a by now disintegrated parent comet.