For astronomers, probing the mysteries of “space ice”—its molecular makeup and how it formed—could be the key to understanding not just extraterrestrial geology but also the potential for alien life.
In a study published Monday in Physical Review B, researchers in England report that “space ice” likely contains countless tiny crystals inside and is less liquid-like than astronomers previously believed. At least, that’s according to computer simulations and experimental replications. The discovery resets our understanding of how ice behaves in the frigid vastness of deep space and could influence our theories about planet formation, comet chemistry—and even the origin of life.
“We now have a good idea of what the most common form of ice in the universe looks like at an atomic level,” said Michael B. Davies, a physicist at University College London (UCL) in England and the study’s lead author, in a statement. “This is important, as ice is involved in many cosmological processes, for instance, in how planets form, how galaxies evolve, and how matter moves around the universe.”
Needless to say, space is nowhere like the places we find ice here on Earth, whether it’s a freezer or Antarctica. In space, which exists in near-vacuum conditions, temperatures can get both unbelievably hot and brutally cold. As such, it made more sense to astronomers that space ice wouldn’t contain enough energy to form anything close to the neat, honeycomb-shaped crystals we see on Earth. Rather, the fluctuating conditions should—in theory—produce a strange, abstract form.
The new study challenges that conjecture by suggesting the opposite for low-density amorphous ice—the most common form in the universe—typically found on comets, icy moons, and dust clouds near young stars and planets. The team created several models imitating the temperature conditions under which the ice likely formed, and then compared the results with available X-ray data of previous measurements of actual ice samples.
Surprisingly, their best match was the model in which the ice showed some level of nanocrystal organization—tiny crystals slightly wider than a single strand of DNA—embedded inside its structure, contradicting the long-held belief that space ice is fully amorphous, or having no definite form.
Visual representation of the structure of low-density amorphous ice. Many tiny crystallites (white) are concealed in the amorphous material (blue). © Michael B Davies, UCL and University of CambridgeTo check their work, the researchers also attempted to reverse engineer real samples of amorphous ice formed in different ways, finding that each crystal had a clear “memory” of how it formed. This would only be possible if there was some initial structure to the ice crystals, the researchers concluded in the paper.
“Ice in the rest of the universe has long been considered a snapshot of liquid water—that is, a disordered arrangement fixed in place,” explained co-author Christoph Salzmann, a chemist at University College London (UCL), in the statement. “Our findings show this is not entirely true.”
The team hopes these new insights will inform future investigations into space for theorists, experimentalists, and engineers alike. For one, a better understanding of how space ice forms could help with revisions of climate models for icy moons or comets. But it could also refine our understanding of water itself, noted study co-author Angelos Michaelides in the statement. Michaelides, a chemist at Cambridge University in England, added that “[amorphous] ices may hold the key to explaining some of water’s many anomalies.”
In more practical applications, the quirkiness of space ice could make it useful as “potentially a high-performance material in space,” said Davies. “It could shield spacecraft from radiation or provide fuel in the form of hydrogen and oxygen. So we need to know about its various forms and properties.”
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