Gas permeability and mechanical properties of dust grain aggregates at hyper- and zero-gravity

TL;DR

This study investigates how gravitational forces affect gas permeability and mechanical properties of dust aggregates, providing insights into planetary formation processes and regolith behavior in low-gravity environments.

Contribution

It introduces experimental measurements of gas permeability in dust aggregates under varying gravity conditions, revealing how compaction influences permeability and mechanical strength.

Findings

Permeability decreases with increased gravitational confinement.

Pressure gradients can determine tensile strength of regolith simulants.

Flow symmetry breaks when dust moves against pressure gradients, even at low Reynolds numbers.

Abstract

Particle-particle and particle-gas processes significantly impact planetary precursors such as dust aggregates and planetesimals. We investigate gas permeability ($\kappa$) in 12 granular samples, mimicking planetesimal dust regoliths. Using parabolic flights, this study assesses how gravitational compression -- and lack thereof -- influences gas permeation, impacting the equilibrium state of low-gravity objects. Transitioning between micro- and hyper-gravity induces granular sedimentation dynamics, revealing collective dust-grain aerodynamics. Our experiments measure $\kappa$ across Knudsen number (Kn) ranges, reflecting transitional flow. Using mass and momentum conservation, we derive $\kappa$ and calculate pressure gradients within the granular matrix. Key findings: 1. As confinement pressure increases with gravitational load and mass flow, $\kappa$ and average pore space decrease. This implies that a planetesimal's unique dust-compaction history limits sub-surface volatile outflows. 2. The derived pressure gradient enables tensile strength determination for asteroid regolith simulants with cohesion. This offers a unique approach to studying dust-layer properties when suspended in confinement pressures comparable to the equilibrium state on planetesimals surfaces, which will be valuable for modelling their collisional evolution. 3. We observe a dynamical flow symmetry breaking when granular material moves against the pressure gradient. This occurs even at low Reynolds numbers, suggesting that Stokes numbers for drifting dust aggregates near the Stokes-Epstein transition require a drag force modification based on permeability.