🧊 Discovery of a new form of ice: water can freeze at room temperature

The recent identification of a novel molecular architecture of water, stabilized at a temperature close to our own but under immense compression, opens unexpected perspectives on the physics of icy bodies in the Solar System. This major breakthrough challenges our classical perception of aqueous solidification.

The discovery of this new solid phase, named ice XXI, is the result of an international collaboration using cutting-edge instruments. Scientists reproduced in the laboratory pressures comparable to those found in the depths of certain extraterrestrial moons. Their goal was to map the structural transitions of water during ultra-rapid compression and decompression. This dynamic approach allowed the observation of intermediate states that were previously elusive, shedding new light on crystallization mechanisms under extreme stress.

Secrets of an unusual crystallization

The experimental method relied on the combined use of diamond anvil cells and the European X-ray laser XFEL. Researchers compressed water samples to nearly twenty thousand times atmospheric pressure in just a few milliseconds. This speed of execution prevented the immediate formation of the expected stable phases, allowing the water to remain liquid in a state of exceptional overcompression.

Structural analysis performed using the PETRA III synchrotron revealed the unique molecular organization of ice XXI. Its elementary tetragonal unit cell, comprising 152 water molecules, constitutes an architecture unparalleled among known crystalline phases. This configuration emerges specifically during the transition between overcompressed water and ice VI, temporarily persisting despite its metastable character. Its persistence at room temperature represents a notable physicochemical peculiarity.

The metastability of this solid phase suggests the potential existence of other transient crystalline organizations not yet cataloged. Researchers emphasize that the crystallization pathway taken by water depends closely on the degree of overcompression reached before nucleation. This work, detailed in Nature Materials, establishes that the structural diversity of ices extends beyond the framework of low temperatures, also reaching into temperate pressurized environments.

Implications for the icy worlds of the Solar System

The presence of ice VI in the depths of certain icy moons like Europa or Ganymede has long been considered by planetary scientists. Its deformed molecular structure could serve as a precursor to metastable phases similar to ice XXI. The discovery of this new crystalline configuration strengthens the hypothesis that the icy mantles of celestial bodies harbor an unsuspected structural diversity. These molecular arrangements potentially influence their thermal and mechanical properties.

The conditions generating ice XXI could exist naturally within the subglacial oceans of Jupiter's and Saturn's natural satellites. Convective movements and pressure variations in these confined environments would partially reproduce the researchers' experimental protocol. The presence of metastable phases would modify the thermal conductivity and rheology of the icy layers, potentially affecting their internal dynamics and energy exchanges with the underlying liquid ocean.

This advance opens perspectives for interpreting data from future space missions. The European Space Agency's JUICE probe, currently en route to Jupiter, could provide observations compatible with the existence of these unusual phases. Understanding the physical properties of ice XXI and its potential counterparts would allow for refining models of the internal structure of icy bodies, particularly illuminating the mechanisms that maintain their oceans in a liquid state.