Context : Irregular satellites of Jupiter with their highly eccentric , inclined and distant orbits suggest that their capture took place just before the giant planet migration .

Aims : We aim to improve our understanding of the surface composition of irregular satellites of Jupiter to gain insight into a narrow time window when our Solar System was forming .

Methods : We observed three Jovian irregular satellites , Himalia ( JVI ) , Elara ( JVII ) , and Carme ( JXI ) , using a medium-resolution 0.8-5.5 \mu m spectrograph , SpeX on the National Aeronautics and Space Administration ( NASA ) Infrared Teselscope Facility ( IRTF ) .
Using a linear spectral unmixing model we have constrained the major mineral phases on the surface of these three bodies .

Results : Our results confirm that the surface of Himalia ( JVI ) , Elara ( JVII ) , and Carme ( JXI ) are dominated by opaque materials such as those seen in carbonaceous chondrite meteorites .
Our spectral modeling of NIR spectra of Himalia and Elara confirm that their surface composition is the same and magnetite is the dominant mineral .
A comparison of the spectral shape of Himalia with the two large main C-type asteroids , Themis ( D \sim 176 km ) and Europa ( D \sim 352 km ) , suggests surface composition similar to Europa .
The NIR spectrum of Carme exhibits blue slope up to 1.5 \mu m and is spectrally distinct from those of Himalia and Elara .
Our model suggests that it is compositionally similar to amorphous carbon .

Conclusions : Himalia and Elara are compositionally similar but differ significantly from Carme .
These results support the hypotheses that the Jupiter ’ s irregular satellites are captured bodies that were subject to further breakup events and clustered as families based on their similar physical and surface compositions .