According to new observations, Eris is not only close to Pluto in size, it's also so highly reflective that it's one of the brightest objects in the solar system.

We can't see Eris with the naked eye due to its great distance. Right now, the tiny world is almost at its farthest point from the sun, roughly 9 billion miles (14.5 billion kilometers). By contrast, Pluto's farthest distance from the sun is just over 4.5 billion miles (7.3 billion kilometers).

Still, combined with other data, the dwarf planet's brightness suggests that Eris once had a Pluto-like atmosphere that's frozen solid, existing as a thin layer of frost on the surface, astronomers say.

(See "Pluto Has Toxic Carbon Monoxide in Its Atmosphere.")

Eris