 Amalthea 's irregular shape and large size led in the past to a conclusion that it is a fairly strong , rigid body , where it was argued that a body composed of ices or other weak materials would have been pulled into a more spherical shape by its own gravity . However , on 5 November 2002 , the Galileo orbiter made a targeted flyby that came within 160 km of Amalthea and the deflection of its orbit was used to compute the moon 's mass ( its volume had been calculated previously — to within 10 % or so — from a careful analysis of all extant images ) . In the end , Amalthea 's density was found to be as low as 0 @.@ 86 g / cm3 , so it must be either a relatively icy body or very porous " rubble pile " or , more likely , something in between . Recent measurements of infrared spectra from the Subaru telescope suggest that the moon indeed contains hydrous minerals ( or organic materials ) , indicating that it cannot have formed in its current position , since the hot primordial Jupiter would have melted it . It is therefore likely to have formed farther from the planet or to be a captured Solar System body . Unfortunately , no images were taken during this flyby ( Galileo 's cameras had been deactivated due to radiation damage in January 2002 ) , and the resolution of other available images is generally low . 
