Evidence for the formation of comet 67P/Churyumov-Gerasimenko through gravitational collapse of a bound clump of pebbles

The processes that led to the formation of the planetary bodies in the Solar System are still not fully understood. Using the results obtained with the comprehensive suite of instruments on-board ESA’s Rosetta mission, we present evidence that comet 67P/Churyumov-Gerasimenko likely formed through the gentle gravitational collapse of a bound clump of mm-sized dust aggregates (“pebbles”), intermixed with microscopic ice particles. This formation scenario leads to a cometary make-up that is simultaneously compatible with the global porosity, homogeneity, tensile strength, thermal inertia, vertical temperature profiles, sizes and porosities of emitted dust, and the steep increase in water-vapour production rate with decreasing heliocentric distance, measured by the instruments on-board the Rosetta spacecraft and the Philae lander. Our findings suggest that the pebbles observed to be abundant in protoplanetary discs around young stars provide the building material for comets and other minor bodies

Data from: Random-close packing limits for monodisperse and polydisperse hard spheres

We investigate how the densities of inherent structures, which we refer to as the closest jammed configurations, are distributed for packings of 10000 frictionless hard spheres. A computational algorithm is introduced to generate closest jammed configurations and determine corresponding densities. Closest jamming densities for monodisperse packings generated with high compression rates using Lubachevsky–Stillinger and force-biased algorithms are distributed in a narrow density range from φ = 0.634-0.636 to φ ≈ 0.64; closest jamming densities for monodisperse packings generated with low compression rates converge to φ ≈ 0.65 and grow rapidly when crystallization starts with very low compression rates. We interpret φ ≈ 0.64 as the random-close packing (RCP) limit and φ ≈ 0.65 as a lower bound of the glass close packing (GCP) limit, whereas φ = 0.634-0.636 is attributed to another characteristic (lowest typical, LT) density φLT. The three characteristic densities φLT, φRCP and φGCP are determined for polydisperse packings with log-normal sphere radii distributions