How the morphology of dusts influences packing density in small solar system bodies

Abstract:

Large planetary seedlings, comets, and nanoscale soot particles are made from rigid, aggregated subunits that are compacted under low compression into larger structures spanning over 10 orders of magnitude in dimensional space. Here, we demonstrate that the packing density (Φ_f) of compacted rigid aggregates is independent of spatial scale for systems under weak compaction, a regime that includes small solar system bodies.  The Φ_f of rigid aggregated structures across 6 orders of magnitude were measured using nanoscale spherical soot aerosol composed of aggregates with ≈ 17 nm monomeric subunits and aggregates made from uniform monomeric 6 mm spherical subunits at the macroscale. We find Φ_f = 0.36 ± 0.02 at both the nano- and macroscale. These values are remarkably similar to q_f observed for comet nuclei and measured values of other rigid aggregated systems across a wide variety of spatial and formative conditions. We present a packing model that incorporates the aggregate morphology and show that Φ_f is independent of both monomer and aggregate size. These observations suggest thatq_f of rigid aggregates is independent of spatial dimension across varied formative conditions ranging from interstellar space to pharmaceutical manufacturing.