The Alpha Particle X-Ray Spectrometer (APXS) and Mössbauer Spectrometer will be used to make detailed measurements of the composition of martian rocks
and soils. The APXS will measure the concentrations of most of the major rock-forming elements, while the Mössbauer will be used to identify minerals
that contain iron.
The Mössbauer Group is located at Johannes
Gutenberg University. The APXS is being built at the Max Planck Institute für Chemie in Mainz.