The answer definitely isn't 32 degrees Fahrenheit, even if that's the freezing point of water. If the conditions are right, water can remain liquid all the way down to minus 55 degrees. Just another way water is bizarrely amazing.
Chemists at the University of Utah have found that -55 degrees is when water absolutely must start changing its molecular structure. The molecules start forming tetrahedron shapes, where each water molecule becomes loosely bonded to four others. This creates a form of water known as "intermediate ice", and though it hasn't yet taken on all the properties of full-blown ice, it can no longer be considered water.
But up to that point, there's still 87 degrees below the traditional freezing point at which water can remain liquid. And even then, the researchers say liquid water could conceivably still be there below -55 degrees...it's just that such water wouldn't last long enough for its presence to be detected by our instruments.
All this isn't just a bit of molecular bookkeeping. It's crucial to our understanding of global warming that we know precisely at what temperatures and at what rates water freezes and crystallizes into ice. This is because atmospheric water and atmospheric ice absorb different amounts of solar radiation, so we need to know how much of either is in the atmosphere with as much accuracy as possible.
Water is probably the liquid we humans are most familiar with, and yet it behaves almost nothing like a typical liquid. That's part of the reason why it can remain liquid so far below its freezing point. Researcher Valeria Molinero explains:
"hat makes water so strange is that the way liquid water behaves is completely different from other liquids. For example, ice floats on water while most solids sink into their liquid forms because they are denser than the liquids. [The property that] is most fascinating is that you can cool it down well below 32 degrees Fahrenheit and it still remains a liquid.
If you have liquid water and you want to form ice, then you have to first form a small nucleus or seed of ice from the liquid. The liquid has to give birth to ice. For rain, you have to make liquid from vapor. Here, you have to make crystal [ice] from liquid. [In very pure water], the only way you can form a nucleus is by spontaneously changing the structure of the liquid. When you cool down water, its structure becomes closer to the structure of ice, which is why the density goes down, and this should be reflected in an increased crystallization rate."
For more, check out the University of Utah website.
Image by qgil on Flickr.