As more stick together with , they form a regular pattern, as shown here.
Simplified diagram of water ice
We see these patterns when we look at snowflakes under a microscope, or see frost on a window pane. The reason these patterns form is that the water molecules have a V shape, and hydrogen bonds form at the ends of these Vs.
As more and more molecules stick a thick layer of sticky ice grows up around each dust grain in the disc of the Galaxy. As well as water ice, many other sticky molecules stick to each grain. These molecules are not sticky on Earth, but they were in the cold dust clouds of space. and both formed ices around dust grains. We can think of the dust grains as forming the center of tiny snowballs.
eBook only $2.99
398 pages, 300 images
"I find the science fabulous...an extremely useful teaching tool."
Professor David Christian
Become a Citizen of the Universe
and get your free badge!