Contrary to popular belief, liquids can actually exist below their freezing point – in what is known as a 'supercooled' state.
Now, two groups of scientists have produced what is the coldest liquid water to date, reaching temperatures of around -45 degrees Celsius, far below the normal freezing point.
So, how exactly is this possible?
When water reaches its freezing point, whether the water molecules form ice crystals or not depends on a range of factors. While water usually turns into ice below 0°C, it requires an initial crystal to form and start attracting other molecules, among other conditions.
Exploiting this knowledge, the scientists shot jets consisting of tiny micrometre-sized water droplets into a vacuum environment, which almost immediately supercools it.
The extremely low pressure of the vacuum causes water particles on the surface of each droplet to quickly evaporate, removing heat and causing the temperature to drop rapidly.
Keeping each droplet as small as possible means the water can be cooled further without it turning to ice, as well as minimising the risk that droplets will begin to crystallise around any microscopic dust particles.
Unfortunately, the researchers couldn't just measure the temperature of the droplets with a thermometer. Instead, they used advanced laser techniques.
Supercooled water is not only found in the lab. In fact, in some parts of the atmosphere, water is known to exist as liquid in temperatures of up to -31°.
Water is one of the most ubiquitous substances on our planet, but we are often unaware of how unusual it is.
For example, unlike almost any other known substance, water's solid form floats on its liquid form and water ice expands rather than contracting. It also has the highest surface tension of all known liquids. In addition, when it is super-cooled it may exist in two different states simultaneously – as the latest experiments have confirmed.