The long term dynamical stability of the known Neptune Trojans

The long term dynamical stability of the known Neptune Trojans

The Neptune Trojans are a population of small bodies that librate around the L4 and L5 Lagrange points of Neptune’s orbit. Shortly after the discovery of the first such object, 2001 QR322, simulations suggested that the body moved on a dynamically stable orbit. Following this, further discovered objects were generally assumed to also be stable. In recent years, the situation has proved to be more complicated than previously thought. Two of Neptune’s Trojans have been found to exhibit orbital instability on billion year timescales, with another being revealed as a temporarily captured interloper. Here, the results of detailed dynamical simulations of the orbital evolution of the eleven known Neptunian Trojans are presented, examining the influence of their initial orbital semi-major axes and eccentricities on their stability. The results reveal the importance of considering the orbital stability of newly discovered objects on a case-by-case basis, with some members showing highly unstable behaviour, whilst others seem likely to be primordial in nature.
The earlier finding that 2001 QR322 and 2008 LC18 are primordial in nature but unstable on billion year timescales are confirmed. In both cases, their stability is a strong function of their semi-major axis, with the two lying on the
boundary between stable and unstable regions. In addition we reveal the stability of eight other Neptune Trojans. Six of the known Trojans move on highly stable orbits. In contrast, two objects, 2004 KV18 and 2010 EN65, are confirmed to be temporarily captured members of the Neptune's Trojan
population. While one, 2012 GX17, is found to be a misidentified Trans-Neptunian Object.