Four temporary Neptune co-orbitals: (148975) 2001 XA255, (310071) 2010 KR59, (316179) 2010 EN65, and 2012 GX17

Abstract

Numerical simulations suggest that Neptune primordial co-orbitals may outnumber the equivalent population hosted by Jupiter, yet the objects remain elusive. Since the first discovery in 2001 just 10 minor planets have been identified as Neptune co-orbitals. On the other hand, some simulations predict that a negligible fraction of passing bodies are captured into the 1:1 commensurability with Neptune today. Hundreds of objects have been discovered in the outer solar system during the various wide-field surveys carried out during the past decade, and many of them have been classified using cuts in the pericentre and other orbital elements. This leads to possible misclassifications of resonant objects. Here, we explore this possibility to uncover neglected Neptune co-orbitals. We confirm that 4 objects previously classified as Centaurs by the MPC currently are temporary Neptune co-orbitals. (148975) 2001 XA255 is the most dynamically unstable of the four. It appears to be a relatively recent (50 kyr) visitor from the scattered disk in its way to the inner solar system. (310071) 2010 KR59 is following a complex horseshoe orbit, (316179) 2010 EN65 is in the process of switching from leading to trailing Trojan, and 2012 GX17 is a promising trailing Trojan candidate in urgent need of follow-up. The four objects move in highly inclined orbits and have significant eccentricities. These dynamically hot objects are not primordial 1:1 librators, but are captured and likely originated from beyond Neptune.