Granular Matter in Space

The investigation of granular matter benefits from experiments in microgravity in several ways and may be categorized into three regimes of increasing density: (1) Granular gases [1] are dilute systems and subject to sedimentation which can be avoided in microgravity. Their agitation by magnetic excitation allows for the study of cooling, velocity distributions and the onset of particle agglomeration.(2) Granular fluids [2] are denser than granular gases and are monitored by scattering techniques. On Earth, granular fluids are anisotropic and inhomogeneous. In microgravity, agitated homogeneous granular fluids can be prepared for densities up to the jamming transition. (3) Granular packings [3] close to the jamming transisionexperience a large pressure gradient on Earth which is absent in microgravity. Hence, sound transmission can be studied at very low confinement. Similarly, microgravityoffers unique opportunities for the rheology on dense granular systems.