Po-Yen Liu (National Central University, Institute of Astronomy); Wing-Huen Ip (National Central University, Institute of Astronomy)
Triton is known to be the largest satellite of Neptune and is unique for its retrograde and circular orbit which lies between other small inner prograde satellites and exterior satellites with both prograde and retrograde orbits. Previous works have shown that this unusual configuration is more likely to be explained by a mechanism called "binary-planet gravitational encounter" (Agnor & Hamilton, 2006), suggesting that Triton was once a member of a binary system of trans-Neptunian objects (TNOs) and was captured by Neptune, while the other member was expelled during the process. This scenario provides a pathway to explore the original population of the TNOs in the early Solar System. In this study, we numerically investigate the close encounter events of the potential candidates of being captured by Neptune, which include Centaurs and scattering disk objects (SDOs). Centaurs are the minor bodies in the outer Solar System whose perihelia are between the orbits of the four giant planets, and they are believed to be the transitional population between the Kuiper belt and the Jupiter-family comets (JFCs). On the other hand, SDOs are the minor bodies which have orbits just slightly beyond Neptune and are thus under its gravitational influence. Given that TNOs must first become SDOs or Centaurs to have cross orbits with Neptune, our investigation of the capture efficiency of Triton is able to speculate the original population of the TNOs. The statistical results from this numerical simulation will be presented here.