It's easy to imagine that water must be one of best understood materials in science. After all, this liquid is possibly the best studied substance on Earth. But the truth is that many of its properties still mystify scientists.
One unsolved puzzle is its freezing point. Scientists have known for many years that you can cool liquid water well below zero degrees centigrade without it freezing. That's because water needs some nucleation event to trigger the process of ice formation. Without ice nucleation, it remains liquid.
But how low can you go?