 However, Mike Brown claims that these numbers are only right for rocky bodies like asteroids, and that icy bodies like Kuiper Belt objects reach hydrostatic equilibrium at much smaller sizes, probably somewhere between 200 and 400 km in diameter.It all depends on the rigidity of the material that makes up the body, which is in turn strongly influenced by its internal temperature.Assuming that Methone's shape reflects the balance between the tidal force exerted by Saturn and the moon's gravity, its tiny 3 km diameter suggests Methone is composed of icy fluff.