There exists ice that does not melt even at hundreds of degrees, and it seems that entire planets stand on it. Under normal pressure, ice has to be cold. But if you compress water tens of thousands of times stronger than atmospheric pressure, the molecules have nowhere to go, and the pressure itself compresses them into a crystalline lattice, causing the water to “freeze,” even while being scalding hot. Not supercooled, not tricky—just simultaneously solid and hot. It’s called “Ice VII”. At a pressure of about 10 GPa, it remains a crystal at temperatures above +300°C.
This type of ice has been found in nature. In 2017, its tiny crystals were discovered locked inside diamonds that had been lifted from the depths of the Earth’s mantle—the water was sealed in there under monstrous residual pressure. And if you compress and heat water even more—to hundreds of GPa and thousands of degrees—it transitions into an even more bizarre phase: superionic ice. Oxygen atoms sit in a rigid lattice while protons flow freely through it like a fluid. This ice conducts electricity and, according to calculations, appears black and incandescent. It was momentarily produced in the laboratory with laser shock waves, and models suggest that significant portions of the interiors of Uranus, Neptune, and many “water” exoplanets are composed of it—this particularly explains their strange, skewed magnetic fields.
Our domestic experience of “ice = cold” is a narrow special case at one atmosphere of pressure. Science already knows about twenty crystalline forms of ice, and in the interiors of planets, water can easily be both solid and hot at the same time.
Hi, I'm Rauf Aliev. 