Observing the Glass and Jamming Transitions of Dense Granular Material in Microgravity

The present Letter investigates a weakly pulsed granular system of polystyrene spheres under longtime microgravity conditions on the International Space Station. The spheres are measured using diffusing wave spectroscopy (DWS) and are described by mean square displacements (MSDs). Our aim is to use this technique to provide the first experimental evidence for glassy dynamics in dense granular media in microgravity and subsequently compare these results with ground-based measurements to see how the nature of these dynamics changes without the influence of gravity. Our results show that as we densify the sample in microgravity, glassy dynamics appear at a volume fraction 1.6% lower than on ground. We also show how the influence of gravity can affect how dense a granular system one can prepare by comparing the final jamming point of our sample on the ISS compared to our ground setup. We show that jamming occurs at a volume fraction 0.5% lower in space compared to on ground, showing that we can create denser states when a granular system is in the presence of a stronger gravitational field.