Water droplets

Supercooled water was made by spraying microscopic water droplets into a vacuum.

Physics

The coldest liquid water ever measured

Droplets in a vacuum are supercooled to –42.6 degrees Celsius.

Physicists have observed a record low temperature for liquid water.

Under strict conditions, water can exist in a liquid state well below its freezing point. But reliably measuring the temperature of ‘supercooled’ water is challenging. To do so, Robert Grisenti at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany, and his colleagues sprayed micrometre-sized droplets of water into a vacuum. Molecules of water evaporated from the surface of the droplets, making them smaller and colder.

The droplets cool in proportion to how much they shrink, which enabled the researchers to determine the water’s temperature by measuring droplet size with a laser. The team calculated the water’s temperature to be –42.6 degrees Celsius.

Because supercooled water occurs naturally in Earth’s upper atmosphere, gaining a better understanding of its properties, as well as how and when it transforms into ice, could help researchers to develop more reliable climate models, say the authors.