It's common knowledge that liquid water expands when it forms ice. Conversely, frozen water compacts as it melts. Now, a team of European researchers has made an ultrathin film of supercooled water that's much denser than normal water.
The experimenters suspect that they have created the first sample of a previously hypothesized form—or phase—of water known as high-density liquid water, or HDL.
"We do not have complete proof that we've found this phase, but we think that it looks very promising," says team member Simon Engemann of the Max Planck Institute for Metals Research in Stuttgart, Germany.
The results are "the biggest breakthrough in experimental measurements of water in a long time," comments physicist H. Eugene Stanley of Boston University. It's "the first discovery of water that's significantly denser than ordinary water. That's remarkable, whatever it means," he adds.