Neither: Eris is a dwarf planet in the kyper belt and is known as a KBO or Kyper belt object.

Asteroid and Kuiper (or Kyper)

Nothing obvious, but more than likely the answer is Kyper Belt (Kuiper belt),

The Kyper Belt is the region far outside the orbit of Neptune where objects, also known as transneptunian objects, orbit the sun. These objects can differ from dwarf planets, like Pluto, to asteroids or other debris. Their origin is believed to be that they are leftovers from when the solar system was very young and were thrown out there by the gravity of the current planets.

Considering the Kyper belt is part of the Solar System the question cannot be answered.