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Scientists have captured reversible changes in the structure of supercooled water for the first time, using pulsed laser heating and infrared spectroscopy. Credit: Timothy Holland, Pacific Northwest National Laboratory

Supercooled water is really two liquids in one. That's the conclusion reached by a research team at the U.S. Department of Energy's Pacific Northwest National Laboratory after making the first-ever measurements of liquid water at temperatures much colder than its typical freezing point.

The finding, published today in the journal Science, provides long-sought experimental data to explain some of the bizarre behavior water exhibits at extremely cold temperatures found in outer space and at the far reaches of Earth's own atmosphere. Until now, liquid water at the most extreme possible temperatures has been the subject of competing theories and conjecture. Some scientists have asked whether it is even possible for water to truly exist as a liquid at temperatures as low as -117.7 F (190 K) or whether the odd behavior is just water rearranging on its inevitable path to a solid.

The argument matters because understanding water, which covers 71 percent of the Earth's surface, is critical to understanding how it regulates our environment, our bodies and life itself.