in favour of roundness and solidity.

The majority of mid-sized TNOs up to about in diameter have significantly lower densities (~ ) than larger bodies such as Pluto (1.86 g/cm³). Brown had speculated that this was due to their composition, that they were almost entirely icy. However, Grundy et al. point out that there is no known mechanism or evolutionary pathway for mid-sized bodies to be icy while both larger and smaller objects are partially rocky. They demonstrated that at the prevailing temperatures of the Kuiper