Ice comes in more forms than what you’ll find in a freezer or a glacier. Since 1900, scientists have observed more than 20 phases of ice, many of them shaped under extreme conditions. The growing list includes hot ice and even ice that conducts electricity. Ice is the name for any phase of water that is solid and crystalline, meaning that it has a repeating molecular structure. Over the past decade, computer simulations have predicted tens of thousands of possible forms of ice. Though uncommon on our planet, exotic ice may exist in off-Earth environments, from cold and amorphous comet tails to the hot and crushing cores of icy planets. As physicists put water to the test with improved experimental techniques, they keep finding surprises.…