Most of the Universe's Water Is a Glass, Not Ice

The ice in your freezer is crystalline: its water molecules lock into a tidy, repeating lattice. But that orderly arrangement is rare in the wider cosmos. By far the most abundant frozen water in the Universe is low-density amorphous ice, a disordered, glassy solid in which the molecules are frozen into a jumbled, non-repeating mess.

This glassy ice forms the bulk material of comets, coats icy moons, and pervades the cold clouds of dust where new stars and planets are born. It exists because space is so cold that water vapour freezes almost instantly on contact with grains, leaving molecules no time to settle into a crystal.

Most of the water that has ever existed isn’t liquid or ordinary ice — it’s a glass.

In 2025, researchers at UCL and the University of Cambridge reported in Physical Review B that this ice isn’t perfectly disordered after all: simulations and experiments suggest it hides tiny crystals just nanometres wide. The finding could reshape ideas about how water — and perhaps life’s ingredients — travelled to early Earth aboard comets.