In laboratories designed to simulate the impossible, scientists have coaxed water into a form that defies its own nature — a solid that holds its shape above 2,000 degrees Celsius. This so-called superionic ice, long predicted by theory but never before witnessed in experiment, may be the hidden substance shaping the interiors of Neptune and Uranus, two worlds that have resisted our understanding for generations. The discovery reminds us that the most familiar substance on Earth still holds secrets, and that the cosmos routinely operates by rules we are only beginning to read.