Italian-built infrared spectrometer optimized for atmospheric studies of Mars and Venus over a wavelength range of 1.2–45 microns. The 31.4 kg instrument consists of four units—an interferometer with electronics, a control unit, a power supply, and a pointing device—and is currently in use aboard two European Space Agency missions: Mars Express and Venus Express. The instrument’s most critical function centres on the 15 µm waveband, which is strongly absorbed by carbon dioxide. As carbon dioxide makes up more than 98% of the Martian atmosphere, the measurements will form the basis of global atmospheric temperature and pressure studies.