Neptune Trojan - Dynamics and Origin

Dynamics and Origin

The orbits of Neptune trojans are highly stable; Neptune may have retained up to 50% of the original post-migration trojan population over the age of the Solar System. Neptune currently cannot efficiently capture trojans even for short periods. Neptune's L₅ can host stable trojans equally well as its L₄.

It is possible for Neptune trojans to librate up to 30° from their associated Lagrangian points with a 10,000-year period.

The unexpected high-inclination trojans are the key to understanding the origin and evolution of the population as a whole. The existence of high-inclination Neptune trojans points to 'freeze-in' capture or variations on this process, or during a slow, smooth migration, instead of in situ or collisional formation, as the origin of Neptune trojans. The captured population already had to be dynamically excited for high-inclination trojans to exist. While resonant trans-Neptunian objects are thought to have been captured by sweeping resonances during planet migration, this process would cause the escape of Neptune trojans. Irregular planetary migration would result in the depletion of the associated trojan reservoir. The estimated equal number of large L₅ and L₄ trojans indicates that there was no gas drag during capture and points to a common capture mechanism for both L₄ and L₅ trojans. The original population of trojans probably contained many objects on dynamically unstable orbits, and the current trojan population continues to contribute centaurs. On the other hand, a trojan on a stable orbit need not be primordial.