Horseshoe co-orbitals of Earth: current population and new candidates

Abstract

ABSTRACT Most co-orbital objects in the Solar system are thought to follow tadpole-type orbits, behaving as Trojans. However, most of Earth’s identified co-orbitals are moving along horseshoe-type orbits. The current tally of minor bodies considered to be Earth co-orbitals amounts to 18; of them, 12 are horseshoes, 5 are quasi-satellites, and 1 is a Trojan. The semimajor axis values of all these bodies librate between 0.983 and 1.017 au. In this work, we have studied the dynamical behaviour of objects following orbits with semimajor axis within this range that may be in a 1:1 mean-motion resonance with Earth. Our results show that asteroids 2016 CO246, 2017 SL16, and 2017 XQ60 are moving along asymmetrical horseshoe-type orbits; the asteroid 2018 PN22 follows a nearly symmetric or regular horseshoe-type orbit. Asteroids 2016 CO246, 2017 SL16, and 2017 XQ60 can remain in the horseshoe co-orbital state for about 900, 3300, and 2700 yr, respectively. Asteroid 2018 PN22 has a more chaotic dynamical behaviour; it may not stay in a horseshoe co-orbital state for more than 200 yr. The horseshoe libration periods of 2016 CO246, 2017 SL16, 2017 XQ60, and 2018 PN22 are 280, 255, 411, and 125 yr, respectively.