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Coagulation models assume a higher sticking threshold for micrometer-sized ice particles than for micrometer-sized silicate particles. However, in contrast to silicates, laboratory investigations of the collision properties of micrometer-sized ice particles (in particular, of the most abundant water ice) have not been conducted yet. Thus, we used two different experimental methods to produce micrometer-sized water ice particles, i. e. by spraying water droplets into liquid nitrogen and by spraying water droplets into a cold nitrogen atmosphere. The mean particle radii of the ice particles produced with these experimental methods are $(1.49 pm 0.79) , mathrm{mu m}$ and $(1.45 pm 0.65) , mathrm{mu m}$. Ice aggregates composed of the micrometer-sized ice particles are highly porous (volume filling factor: $phi = 0.11 pm 0.01$) or rather compact (volume filling factor: $phi = 0.72 pm 0.04$), depending on the method of production. Furthermore, the critical rolling friction force of $F_{Roll,ice}=(114.8 pm 23.8) times 10^{-10}, mathrm{N}$ was measured for micrometer-sized ice particles, which exceeds the critical rolling friction force of micrometer-sized $mathrm{SiO_2}$ particles ($F_{Roll,SiO_2}=(12.1 pm 3.6) times 10^{-10}, mathrm{N}$). This result implies that the adhesive bonding between micrometer-sized ice particles is stronger than the bonding strength between $mathrm{SiO_2}$ particles. An estimation of the specific surface energy of micrometer-sized ice particles, derived from the measured critical rolling friction forces and the surface energy of micrometer-sized $mathrm{SiO_2}$ particles, results in $gamma_{ice} = 0.190 , mathrm{J , m^{-2}}$.
Models and observations suggest that ice-particle aggregation at and beyond the snowline dominates the earliest stages of planet-formation, which therefore is subject to many laboratory studies. However, the pressure-temperature gradients in proto-pl
Water ice is one of the most abundant materials in dense molecular clouds and in the outer reaches of protoplanetary disks. In contrast to other materials (e.g., silicates) water ice is assumed to be stickier due to its higher specific surface energy
An atom moving in a vacuum at constant velocity and parallel to a surface experiences a frictional force induced by the dissipative interaction with the quantum fluctuations of the electromagnetic field. We show that the combination of nonequilibrium
The geophysics of extrasolar planets is a scientific topic often regarded as standing largely beyond the reach of near-term observations. This reality in no way diminishes the central role of geophysical phenomena in shaping planetary outcomes, from
Planetary science beyond the boundaries of our Solar System is today in its infancy. Until a couple of decades ago, the detailed investigation of the planetary properties was restricted to objects orbiting inside the Kuiper Belt. Today, we cannot ign