Eris

Eris is a dwarf planet of the Kuiper belt, beyond Pluto, in the outer Sol system. The Kuiper belt is the region of small icy bodies that lies beyond the orbit of Neptune.

Eris is named on the Solar War map and in almost no other source. Fandom lists it as an outer-Sol body. No garrison, battle or habitat dossier exists for it.

The location is therefore best treated as a charted trans-Neptunian body, meaning an object that orbits beyond Neptune. It is not a fortress-world, and the pin on the map records position only.