SAM: An International Endeavor
The SAM instrument suite is the result of collaboration between NASA, a number of university partners, and international partners. The French Space Agency supported the development of SAM’s Gas Chromatograph, and several French scientists are part of the SAM science team. This blog entry was contributed by Maëva Millan, a Ph.D. student in France who is supporting SAM laboratory research.
The SAM instrument contributes to the Curiosity’s scientific goal to characterize the potential past or present habitability of Mars. The first three soil and rocks samples collected by Curiosity were partly delivered to SAM and analyzed with the Gas Chromatograph-Mass spectrometer (GCMS) during the first martian year of the Mars Science Laboratory (MSL) mission. Analyzing the GCMS runs, SAM scientists reported the detection of chlorinated organic compounds above instrument background levels in the Cumberland drill hole sample, leading to the first time detection of organic materials in a Mars sample – ever. A very important result! Some of these compounds originate from reactions between oxychlorine salts, widely spread at Mars’ surface, with organic carbon preserved in the rocks.
Before claiming identification of these chemical species, a lot of hard laboratory work was done. In particular, laboratory experiments on spare part
Gas chromatography (GC) coupled with mass spectrometry (MS) allows the physical separation of the compounds, and their identification, by combining structural information (mass) given by the MS and the time it takes for different chemical species to move through the GC (retention time). SAM GCMS signatures are often complex. Information from both the GC and MS are required to ensure the identification.
This is the reason why the French GC team carefully determines the retention times of a wide range of organic molecules, which have been detected on Mars. This method allowed the clear identifications of all chlorohydrocarbons present in martian solid samples, such the chlorobenzene and the dichloroalkanes.
Laboratory measurements are also used to predict the retention times of molecules that may have been delivered to the surface of Mars by meteorites, or involved in prebiotic chemistry and possible indicators of life. Compiling a database of this information will allow us to know where to look for these types of molecules in SAM analyses, and be able to identify them if they are present. The laboratory calibrations are of primary importance because they are the only way to ensure that we understand the data SAM returned from Mars.