On 22 October 2025, scientists announced they had created and detected a new form of solid water called Ice XXI. This ice remains stable at room temperature under certain conditions. Using the world’s largest X-ray free-electron laser (XFEL) facility, the team compressed water between two diamonds at pressures about 20,000 times normal atmospheric pressure. The result is a very high-density ice phase that, once formed, can remain metastable at normal temperature. This discovery shows that water’s phase diagram is more complex than previously thought. It opens new paths for materials science and planetary research.
How they did it
The researchers used a clever setup: a diamond anvil cell to compress water to extreme pressure while probing it with rapid X-ray pulses at the European XFEL. They compressed and relaxed the sample over more than 1,000 cycles, tracking structural changes every microsecond. The X-ray diffraction patterns showed a transition from a high-density ice state to a denser, previously unseen arrangement of water molecules. Once formed, the new phase remained solid even after the pressure decreased and the temperature returned to normal. This is unusual because most exotic ice phases collapse or revert when pressure is removed.
Why this matters for materials science
Ice XXI challenges our understanding of how water behaves. Materials that can switch phases or remain stable under normal conditions after extreme treatment are very valuable in materials science. This ice form may help scientists design new high-density solids, storage media, or unique molecular frameworks. It shows that hidden phases may exist in simple substances like water when subjected to conditions far beyond the ordinary.
Implications for planetary science
Beyond Earth, this discovery could change how we view icy bodies in the solar system and beyond. Moons like Europa, Ganymede, or Enceladus have layers of high-pressure ice beneath their surfaces. The existence of metastable phases like Ice XXI suggests that exotic ice structures might survive during planetary resurfacing or impact processes and could affect geological or thermal behavior. For ice-rich exoplanets, this phase may occur naturally and influence the planet’s structure or magnetic properties.
what remains unknown
Despite this breakthrough, many questions remain:
- Can Ice XXI form naturally, or does it need the controlled cycles used in the lab?
- How stable is it over long periods and in varying environments?
- What is the exact molecular structure (the X-ray data show a new lattice, but details are still being refined)?
- Are there more undiscovered ice phases at even lower pressure or higher temperature? The research suggests that water’s phase map is richer than previously thought.
Related discoveries and context
Ice has many known phases (Ih, Ic, II, III … XVIII, etc.), most of which occur under extreme pressure or very low temperatures. The fact that a new phase appears and remains metastable at normal conditions is rare. Previous extreme ice forms required maintained high pressure or cryogenic environments. This research builds on advances in high-pressure physics, X-ray lasers, and fast-cycling experiments to uncover hidden states of matter.
Why you should care
This is not just an academic curiosity. Discovering new phases of materials changes how we think about natural processes and technological possibilities. From designing new materials with unusual electrical or thermal properties to understanding how ice behaves in extreme planetary conditions, an unexpected ice phase may lead to surprising applications. Simple substances like water can still surprise us, reminding us that science is full of mysteries.
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Conclusion
The creation of Ice XXI is more than just another type of ice; it reminds us that even everyday materials hold surprising secrets. By exploring extreme pressure, temperature, and observation, scientists have revealed hidden molecular worlds.
As research progresses, Ice XXI could change how we view planetary evolution, climate science, and material design. For now, it is one of the most interesting scientific discoveries of 2025. This silent crystal shows us how much more we can learn from a drop of water.
