The estimated masses of planets b – f fall in the range between those of Earth and Neptune. Their estimated densities, all lower than that of Earth, imply that none of them have an Earth-like composition; a significant hydrogen/helium atmosphere is predicted for planets c, d, e, f, and g, while planet b may be surrounded by a steam atmosphere or perhaps by a hydrogen atmosphere. The low densities likely result from high-volume extended atmospheres that surround cores of iron, rock, and possibly H2O. The inner constituents of the Kepler-11 system were, at the time of their discoveries, the most comprehensively understood extrasolar planets smaller than Neptune. Currently, observations do not place a firm constraint on the mass of planet g (<25 ME). However, formation and evolution studies indicate that the mass of planet g is not much greater than about 7 ME.