 Ida is classified as an S @-@ type asteroid based on ground @-@ based spectroscopic measurements . The composition of S @-@ types was uncertain before the Galileo flybys , but was interpreted to be either of two minerals found in meteorites that had fallen to the Earth : ordinary chondrite ( OC ) and stony @-@ iron . Estimates of Ida 's density are constrained to less than 3 @.@ 2 g / cm3 by the long @-@ term stability of Dactyl 's orbit . 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 . 
