That is not known. Eris is too far away for us to know anything about its internal structure.
rocky ic core and ice
Eris is made of rock and ice.
Eris is made mostly of ice.
Eris's moon Dysnomia, appears to be made of material similar to Eris and Eris appears almost grey.
methane
There made of Rock and something else
If you mean a large trans-Neptunian object: dwarf planet 136199 Eris then you have made a mistake. The dwarf planet Eris is thought to be quite white.
The two smallest major planets, Mercury and Mars, are both smaller than the estimated size of the Earth's core (combined inner and outer core).Mercury has a diameter of about 4879 km and Mars is about 6792 km, compared to the Earth's core which is a sphere about 6972 km in diameter.All of the dwarf planets (Pluto, Eris, Haumea, Makemake, and Ceres) are smaller in diameter than even the Earth's solid inner core (~2440 km in diameter), although Eris is almost as large and Pluto only slightly smaller than Eris.-The Earth's inner core has a thickness (radius) of about 1220 km.-The Earth's outer core has a thickness (radius) of about 2266 km.
it is mostly made up of rock
poopy! always is a primary source
As of 2021, no space crafts have visited Eris, the dwarf planet located in the outer solar system. Most of the information we have about Eris comes from observations made from telescopes here on Earth.
Eris is composed mainly of ice and rock, similar to Pluto and other dwarf planets in the outer solar system. It is thought to have a rocky core surrounded by a thick layer of frozen water, methane, and nitrogen. Additionally, Eris is also believed to have a thin atmosphere consisting of methane gas.