Trans-Neptunian object

Eris and its moon Dysnomia are both Trans-Neptunian Objects

Trans-Neptunian object or TNO is a name astronomers give to any minor planet in the Solar System which orbits (travels around) the Sun beyond the planet Neptune. There are over a thousand Trans-Neptunian objects.[1] Many are in the Kuiper belt.

References

  1. Minor Planet Center. [1]