Trans-Neptunian Objects (TNOs)Describe the location and nature of ... Trans-Neptunian Objects (TNOs)
TNOs are are large bodies that orbit outside of Neptune's orbit.
Pluto was the first of these objects to be discovered followed by other bodies and some that have since been classified as dwarf planets.
Some have resonant orbits with Neptune, others are thought to be Kuiper Belt objects. Observing features in these bodies is difficult as they are so distant and reflect a small amount of sunlight.
Over 1,000 bodies have been discovered.