Imagine ice, not just as cubes or crushed, but as a peculiar substance with a molecular structure akin to liquid water. Researchers have made a groundbreaking discovery, unveiling a new form of ice known as medium-density amorphous ice (MDA). This unique ice not only mimics the disordered molecular arrangement of liquid water but also shares a similar density, filling a previously unknown gap in ice’s density spectrum. This discovery, published in Science, has significant implications for our understanding of water and its various anomalies.
Bridging the Density Gap in Ice
Scientists have long known about 20 crystalline forms of ice and two main types of amorphous ice: high-density and low-density. The prevailing belief was that no ice existed between these two density extremes. “The accepted wisdom has been that no ice exists within that density gap,” explains Christoph Salzmann, a materials scientist at University College London and co-author of the study. “Our study shows that the density of MDA is precisely within this density gap, and this finding may have far-reaching consequences for our understanding of liquid water and its many anomalies.”
Creating MDA: Shaking Ice to its Core
The creation of MDA involved a rather unconventional method: vigorously shaking ordinary ice in a container filled with steel balls at a temperature of approximately -376 degrees Fahrenheit (-200 degrees Celsius). This technique, known as ball milling, utilizes mechanical force to break down the ice’s crystalline structure. “We shook the ice like crazy for a long time and destroyed the crystal structure,” describes Alexander Rosu-Finsen, lead author of the study and researcher at UCL. “Rather than ending up with smaller pieces of ice, we realized that we had come up with an entirely new kind of thing, with some remarkable properties.” The resulting MDA appears as a white powder, solid in form but possessing the molecular disarray of liquid water.
Unveiling MDA’s Unique Properties and Implications
The discovery of MDA challenges existing scientific understanding of water’s behavior under extreme conditions. One particularly intriguing characteristic of MDA is the significant amount of heat it releases when it recrystallizes back into ordinary ice. This property has potential geophysical implications for icy celestial bodies, such as Jupiter’s moon Europa, which NASA’s Europa Clipper mission, scheduled for launch in 2024, will explore.
“Amorphous ice in general is said to be the most abundant form of water in the universe,” notes Angelos Michaelides, a chemist at the University of Cambridge and co-author of the study. “The race is now on to understand how much of it is MDA.”
Expanding Our Understanding of Ice
This discovery follows other recent breakthroughs in ice research, including last year’s identification of Ice-VIIt, a form of ice with a tetragonal crystal structure, created by compressing water ice using a diamond anvil. This contrasts with the typical hexagonal symmetry of ordinary water ice, known as Ice-I. The discovery of MDA underscores the complex and fascinating nature of water and its solid forms, prompting further investigation into its diverse manifestations throughout the universe.
Conclusion
The discovery of medium-density amorphous ice opens up exciting new avenues for scientific exploration. Understanding the properties and prevalence of MDA could revolutionize our understanding of water’s role in the universe, from the icy moons of our solar system to the vast expanse of interstellar space. This groundbreaking research encourages further investigation into the hidden secrets of this fundamental substance.
