In space, ice forms by building up a "frost-like" layer on dust grains at a temperature of –441° Fahrenheit (–263° Celsius). The layer that results is a bit like the frost that forms on a car windscreen on a (somewhat less) cold morning on Earth. In this image, the dust layer is represented by the blue colored molecules at the bottom of the image. Water molecules have two hydrogen atoms (shown here in white) and one oxygen atom (shown here in red). Here the ice forms without structure (so-called amorphous ice), quite unlike the more familiar cubes of ice that you might find in a drink. This results in pores forming in the ice — the big "hole" in the middle of this simulation. The hole here is nano-sized — about a million times smaller in diameter than the diameter of a human hair. Gases get trapped in these pores, which can have a profound effect on temperatures and densities in regions of star formation.
Helen Fraser (Open University)