Granular Matter in Space: Microgravity Experiments and Implications for Regolith Behaviour

Understanding the behaviour of planetary regolith under low-gravity conditions is essential for the design of future exploration systems and surface operations. Over the past two decades, the European Space Agency (ESA) has conducted various microgravity experiments on granular matter, combining vibration-driven dynamics and compaction studies across sounding rockets, parabolic flights, and long-duration investigations onboard the International Space Station (ISS).

Sounding rocket and parabolic experiments have enabled the study of dilute granular gases under near-weightless conditions, revealing strongly non-equilibrium behaviours such as the breakdown of energy equipartition and modifications of collisional dynamics in anisotropic particle systems. Complementary parabolic flight campaigns have provided insights into dense granular regimes relevant to regolith, demonstrating three-dimensional compaction, non-linear collision scaling, and vibration-driven convection phenomena, while also quantifying the influence of residual accelerations. 

More recently, ISS experiments have enabled systematic investigations of granular systems subjected to controlled vibration forcing over extended durations. These studies have highlighted key mechanisms such as segregation, convection-like transport driven by energy gradients, and the transition between dilute and dense regimes. Such observations provide direct analogues to processes expected in planetary regolith exposed to mechanical perturbations, including rover interactions, drilling, or seismic shaking. 

These multi-platform results will be presented, bridging the gap between fundamental granular physics and the behaviour of regolith in planetary environments, supporting the development of predictive models and technologies for surface mobility, sampling, and in-situ resource utilisation on the Moon, Mars, and small bodies.