The Composite InfraRed Spectrometer (CIRS for "Composite InfraRed Spectrometer") is one of the instruments on board the Cassini probe. The Cassini probe was inserted in orbit around Saturn on July 2004, six and half years after its launch. The spectrometer was built as a joint effort of CEA-Dapnia, the Goddard Space Flight Center at Washington, the Oxford University, the Queen Mary’s College In UK and the Paris Observatory.
This instrument allows to analyze the infrared light emitted by the planet Saturn but also by its famous rings and satellites, with a resolution (sharpness of details) and sensibility much better than that of its precursor : the IRIS instrument embarked on the VOYAGER probe in the 80s.
The infrared spectrometer CIRS is located at the focus of a telescope Cassegrain of 50 cm in diameter. It consists of two Michelson interferometers, moved by the same actuator. The first one covers the so-called "sub-millimetre” domain (wavelength from 20 to 1000 micrometers). The other, more classic, contains a raw of ten detectors semi-conductors of tellure of mercury and cadmium (HgCdTe) and is sensitive in the mid infrared (7 to 18 micrometers).