Cross Contamination of Martian Rock Samples

This paper presents the results of theoretical analyses conducted to investigate potential of various particle removal techniques. The purpose is to limit the extent of cross contamination caused by the small particles generated through in situ handling and processing of the simulated Martian rock. Since the same hardware would be used to process several rocks, the cross contamination is defined as particles transferred from sample to sample as a particulate contaminant. For the purpose of analysis, we assume that during handling and processing step, rock is crushed using a jaw crusher set at 1 mm gap. The particle distribution of crushed rock is estimated by a Weibull technique. The estimated mass distribution shows that particles in the range of 10 to 100 pm are approximately 0.5 weight percent and they are the major source of the cross contamination. Particles larger than 100 pm are large and easily removed by gravity alone. Removal can be further improved by use of a conductive mechanical brush. Particles less than 10 pm are approximately 0.0001 weight percent. These particles do not cross contaminate because they are generally held strongly at the surface. Therefore, maximum possible cross contamination is 0.5 weight percent if we do not use a cleaning technique other than a mechanical brush. Our theoretical analysis has shown that a high pressure Con jet set at delivery pressure of 13.5 Torr and ultrasonic vibration techniques have potential to remove particles in this size range from a grounded conductive surface and may limit cross contamination to less than 0.1 weight percent.