Dust/ice mixing in cold regions and solid-state water in the diffuse
  interstellar medium
  Whether ice in cold cosmic environments is physically separated from the
silicate dust or mixed with individual silicate moieties is not known. However,
different grain models give very different compositions and temperatures of
grains. The aim of the present study is a comparison of the mid-IR spectra of
laboratory silicate-grains/water-ice mixtures with astronomical observations to
evaluate the presence of dust/ice mixtures in interstellar and circumstellar
environments. The laboratory data can explain the observations assuming
reasonable mass-averaged temperatures for the protostellar envelopes and
protoplanetary disks demonstrating that a substantial fraction of water ice may
be mixed with silicate grains. Based on the combination of laboratory data and
infrared observations, we provide evidence of the presence of solid-state water
in the diffuse interstellar medium. Our results have implications for future
laboratory studies trying to investigate cosmic dust grain analogues and for
future observations trying to identify the structure, composition, and
temperature of grains in different astrophysical environments.
