Experiments in particle resuspension and transport for the assessment of terrestrial-borne biological contamination of the samples on the mars 2020 mission

Abstract

A collection of first-principles models of all known contamination vectors has been developed to assess our ability to meet the stringent requirements for the biological contamination of the soil and rock samples that will be collected during the Mars 2020 mission. The largest contributors to the contamination are the vectors associated with the dislodgement and transport of terrestrial particles from the rover to the surrounding soil, since such particles can carry biological signatures. In this article, we report on the results of particle resuspension experiments performed to both guide and validate these models. In the experiments we employed several pairs of particles and substrates that included idealized microspheres, dust, and biological particles, on surfaces made of glass, kapton or aluminium. We also used a substrate coated with white paint, which exhibited the highest average surface roughness compared to all other substrates. We found that despite the higher relative roughness associated with 40–80 ​μm dust particles on any of the substrates, the removal fractions of ~70-μm glass microspheres from a glass substrate were the highest when they were subjected to the same (lateral) aerodynamic shear stress. We also found that when we exposed ~1-μm biological and non-biological particles to the same aerodynamic shear stresses no removal occurred from a glass substrate. The shear stresses to which these particles were exposed were over three orders of magnitude higher than those associated with the mean wind speeds on Mars.