SAM GC
SAM is an instrumental suite whose objective is the in-situ analysis of the soil and near underground of Mars. Its principle is based on the coupling between a solid or gaseous sampling preparation module and a gaseous phase analysis module. A direct sampling of the atmosphere will also be performed.
The SAM suite is composed of different sub-systems (solid sample manipulation, sample preparation (pyrolysis, deriving, combustion, enrichment) and pumping means) and of three instruments: a Quadrupole Mass Spectrometer (QMS), a Gas Chromatograph (GC) from the Service d'Aéronomie, and a Tunable Laser Spectrometer (TLS).
The Gas Chromatograph (GC) separates and detects the compounds present in the gaseous samples. The separation is made in chromatographic columns (CC, metallic capillary tubes). Six columns were used so as to analyze simultaneously a wide variety of organic and inorganic compounds. Each column is connected upstream to the helium circuit and downstream to the detectors. Their temperature is individually controlled between about 30°C and 250°C.
The SAM GC instrument and detail of a chromatography column
The detection is performed in series using thermal conductivity detectors (TCD) with a dynamic and linear response area, suited to melting ratios ranging from a few hundreds to a few ppm (part per million). The resulting signal is a peak corresponding to each molecule present in the gas. The detectors used by SAM are nano-TCD (similar to those used by the COSAC instrument on board ROSETTA/Philae). An advantage of these detectors is that, by being non-destructive, a mass spectrometer, with a lower detection threshold, can be placed after the detectors, ensuring a partial redundancy.
The use of injection traps (IT) enables gas enrichment through the columns, thus improving specie detection sensitivity.
From the mechanical point of view, the GC is composed of a support plate on which are fixed 6 analysis modules.
Paul Mahaffy, PI from NASA's Goddard Space Flight Centre (GSFC) NASA, is responsible for the SAM instrumental suite .
Michel Cabane, Co-PI from LATMOS (ex-Service d'Aéronomie), is responsible for the French contribution to SAM (SAM-GC).
