COSAC (Cometary Sampling and Composition) is a system specially designed for the detection of complex organic (carbon-bearing) molecules. It was designed so that material from the surface of the comet would be fed into the instrument from the SD2 instrument, combusted, and the resultant gas fed into the analysis section, consisting of a gas chromatograph and a mass spectrometer. In principle it is similar to the Ptolemy instrument also found on the Philae lander. After landing, COSAC was the instrument chosen to receive the single drill sample available before the primary battery failed.
COSAC represents an attempt to miniaturise a considerably sized instrument to fit on a space probe while retaining similar analytical precision. The data from COSAC will help determine whether some of the organic material on Earth was brought here by comets.
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