A Neptune Trojan is an asteroid which is in the same orbit as the planet Neptune.
Their name comes from the Trojan asteroids which have the same orbital period as a planet. As of March 2007, there are six[1][2] known Neptune Trojans. They lie in the elongated, curved region around the L4 Lagrangian point 60° ahead of Neptune. The six Neptune Trojans are 2001 QR322, 385571 Otrera, 2005 TN53, 385695 Clete, 2006 RJ103 and 2007 RW10.
The discovery of 2005 TN53 in a high inclination (>25°) orbit is significant because it suggests a ‘thick’ cloud of Trojans.[3] It is believed that large (radius ≈ 100 km) Neptune Trojans could greatly outnumber the Jupiter Trojans.[4][5]
The New Horizons spacecraft passed through the L5 Neptune region in 2014. It was preparing to observe Pluto and did not observe any asteroids there.