地球質量
The Moon-to-Earth mass ratio of 0.01230 (≈ ) is also notably close to 1 when compared to all other satellite-to-planet ratios. Consequently, some scientists view the Earth-Moon system as a double planet as well, though this is a minority view. Eris's lone satellite, Dysnomia, has a radius somewhere around that of Eris; assuming similar densities (Dysnomia's compositional make-up may or may not differ substantially from Eris's), the mass ratio would be near , a value intermediate to the Moon–Earth and Charon–Pluto ratios.