An instrument aboard the Viking space probe to the planet Mars that looked for signs of organic life forms. After a robot arm scooped out samples, the automated, miniaturized GCMS could separate any organic compounds in its gas chromatograph section and then identify them in the mass spectrometer. The GCMS was sensitive enough to detect a few parts of any organic compound in one billion parts of soil. However, it (and two other related experiments) found no signs of life on the planet.