You are right, Eris is close enough in size to Pluto and to the other 4 Moon-sized objects to be considered in the same class size. In the past, for a long tim

You are right, Eris is close enough in size to Pluto and to the other 4 Moon-sized objects to be considered in the same class size. In the past, for a long time the uncertainties about the sizes of Pluto and of Eris were great, so it was not clear how close in size they are to the other much better known Moon-sized bodies.