Sintering and sublimation of micrometre-sized water-ice particles: the formation of surface crusts on icy Solar System bodies

Sintering is a process driven by mass transport that leads to the formation of a sinter neck between neighbouring particles. The temporal growth of the neck area can lead to an increase of the mechanical strength and increased heat conductivity of granular icy surfaces on Solar System bodies. For water ice, sublimation is closely connected to the sinter process, because it drives the mass transport from the particles in contact to their neck region. Here, we report on novel experiments conducted to investigate the sinter and the sublimation processes of micrometre-sized water-ice particles with the help of a cryogenically cooled scanning electron microscope. Based on these experiments, we developed a sinter model based on which the sintering influence on the tensile strength, the compressive strength, and the thermal conductivity of icy surfaces on Solar System objects can be derived. Applied to comets, we find that the sinter process is faster than the typical erosion rates of cometary surfaces, implying that the uppermost icy surface layers are thermally processed. The surface of Jupiter’s moon Europa is warm enough to experience sintering during its lifetime, whereas the sinter time-scale of Saturn’s moon Enceladus is longer than the age of our Solar System.