Tensile strength and surface energy of CO2 ice in the context of planet formation

Abstract

ABSTRACT Planetesimals grow from agglomerates of small particles, either by pebble accretion or by direct growth. In both cases, the stability of macroscopic agglomerates of fine grains plays a crucial role for the growth, the evolution, and the fate of planetesimals regarding sticking, fragmentation or erosion. While in the inner protoplanetary disc silicates dominate the system, different ice species are the dominant solids in the outer parts. CO2 ice is one of the most abundant species in the outer parts of protoplanetary discs. Here, we present experiments on the stability of highly porous CO2 agglomerates. The CO2 grains are generated by adiabatic expansion of CO2 gas within a cryogenic environment. The agglomerates are compressed to cylinders and the tensile strength is measured using the Brazilian test. The dependence of the tensile strength of porous CO2 agglomerates on the volume filling is well described by a power law. With the well defined geometry, we calculate a surface energy of $\gamma = 0.060\pm 0.022\, \rm J\, m^{-2}$.