World's most powerful X-ray laser spots warm ice under pressure

Researchers using the world’s most powerful X-ray laser at the European XFEL, along with DESY’s PETRA III photon source, have discovered a new metastable phase of ice called ice XXI. This form of ice emerges when water is rapidly compressed to extreme pressures—up to two gigapascals—while maintained at room temperature. Unlike previously known ice phases, ice XXI has a unique tetragonal crystal structure with large repeating units and forms through rapid compression that prevents water from crystallizing into the expected ice VI phase. The discovery challenges existing models of ice formation and suggests that additional high-temperature metastable ice phases may exist. The experiments employed a diamond anvil cell to simulate the extreme pressures found inside icy moons and exoplanets, such as Titan and Ganymede, where ice VI is believed to be stable. By compressing water extremely quickly within milliseconds, the researchers captured the crystallization process using ultrafast X-ray pulses from the European XFEL, effectively filming atomic-scale transitions in