Blown Sand on Mars Can Spread Microbial Spores from Earth

We present experiments demonstrating that B. subtilis HA101 endospores (henceforth spores) may remain intact after impact by, and subsequent transport on the surfaces of, sand grains. To simulate the ricochet of windblown sand grains on a spore-contaminated surface, we constructed a pneumatic gun that accelerated sand grains to 5 m/s. The grains then impacted a spore-laden aluminum surface. They were captured after a single bounce and then imaged with scanning electron microscopy to determine whether any spores adhered to the sand grains and whether they remained intact or were crushed by the impact. Of the 187 identified spores, 74 (40%) appeared intact, which suggests that bacterial spores were not only protected during saltation impact but were also flung onto the retreating sand grain during elastic rebound. Experiments with different aluminum coatings suggested that impacts on uncoated aluminum were more likely to crush spores, whereas anodized and chromate conversion coatings better protected spores. These findings suggest that natural sand transport is a mechanism that could contaminate the environment in the vicinity of a landed spacecraft or in the process of human exploration of a remote aeolian environment, such as that on Mars.