Pore Accessibility in Amorphous Solid Water

The porous nature of amorphous solid water (ASW) can significantly effect the chemical evolution of any planetary or astrophysical surface it forms on due to its ability to trap and retain volatiles. The amount of volatiles that can enter an ASW grain or mantle is limited by how interconnected the pores are to each other and to the exterior surface. Previous laboratory studies examined the interconnectivity of ASW pores in thin ASW films relevant to ice mantles on interstellar grains. Here, we investigate to what extent the interconnectivity of pores and subsequent gas absorption properties of ASW change as one moves toward thicker samples (up to ~10¹⁹ H₂O cm^-2 or ~4 μm) more representative of icy material found in the outer solar system. We find that for all film thicknesses studied, the internal pores are accessible from the sample's surface, and the amount of gas needed to fill the pores increases linearly with the ASW column density. This linear relation supports that the interconnectivity to the surface will persist in ices that are much thicker than those we were able to study, suggesting that the amount of contaminant gas trapped within ASW can significantly alter the chemical evolution of a variety of ASW-rich surfaces in the outer solar system.