Smallest round world

Saturn's tiny moon Methone is the smallest known world in the solar system to be rounded under its own gravity. The egg-shaped world, which was discovered in images taken by the Cassini orbiter on the day of its arrival at Saturn, is 3.88 by 2.58 by 2.42 kilometers in size and appears almost perfectly smooth. The shape is not perfectly spherical because its gravity is so low that its rotation flattens it north-to-south, and tidal forces from Saturn's gravity elongate it toward and away from the planet. Bodies as small as Methone are not usually so smooth, because the inherent strength of the material that makes up such a small moon is usually greater than the tiny force of its self-gravity. Methone's shape indicates that it's likely covered with a deep layer of very fine dust that has no inherent strength.