Ice is a complex substance with at least 20 known forms and possibly thousands more.
Found in various environments, from icy moons to Earth’s crust, ice can be hydrogen-disordered or hydrogen-ordered.
As new forms like ice XIX and ice XX are discovered, our understanding of ice continues to grow.
There are somewhere between 20 and 74,963 forms of ice because water can do all kinds of weird stuff when it freezes.
So far, scientists have experimentally determined the crystal structures for 19 types of ice. Or maybe 20, depending on who you ask.