Testing the veracity of LIBS analyses on Mars using the LIBSSIM program

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• As grain size increases relative to beam size, composition accuracy decreases.
• Sampling density takes on greatest importance in coarse-grained samples.
• Mineralogy can have a strong determinative effect on the calculated composition.

The LIBSSIM program was developed to aid in understanding data returned by the laser-induced breakdown spectrometer (LIBS) on Mars Science Laboratory (MSL). The program models the effects of rock grain size, mineralogy, sampling density, and beam size on inferred bulk chemical analyses using Martian basaltic compositions. The relationship between grain size and beam size was found to be the most important factor in producing a representative LIBSSIM-predicted bulk composition. As grain size increases relative to beam size, accuracy of calculated bulk compositions decreases, but chemical information about the nature of the component grains is improved. Sampling density takes on greatest importance in coarse-grained samples with large compositional differences among grains, where many analyses are required to reduce standard deviations to acceptable levels. These results stress the importance of careful sampling strategies for the LIBS at the MSL landing site at Gale crater.