 This all but rules out a stony-iron composition; were Ida made of 5 g/cm3 iron- and nickel-rich material, it would have to contain more than 40% empty space.The Galileo images also led to the discovery that space weathering was taking place on Ida, a process which causes older regions to become more red in color over time.The same process affects both Ida and its moon, although Dactyl shows a lesser change.