Scientists unlock cosmic ice riddle
Strange substance Scientists have discovered the mechanism behind an unusual material that shrinks when heated and expands when subjected to pressure.
The finding could help in understanding the icy moons of the outer solar system, as well as lead to composite materials that maintain their shape in a range of temperatures.
Reporting in the journal Science, Dr Dominic Fortes of the University College London and colleagues used neutron radiation beams to study the chemical structure of methanol monohydrate - a one to one mix of water and methanol.
They found that when they heated methanol monohydrate, the crystalline structure of the oxygen atoms shorten along their axis, causing them to contract. If subjected to pressure, the oxygen atoms are forced further apart, extending the chains.
Fortes says there are only a handful of materials known to have these properties.
"My suspicion is that, if we look for more, we'll find lots more. The structural motif in methanol monohydrate, which leads to the behaviour, is likely to occur in other substances, so it's only a matter of time," he says.
Benefits for astronomy
Fortes' interest in methanol monohydrate stems from his research into the sub-surface oceans thought to exist on moons in the outer solar system.
"Saturn's moon Enceladus is actively venting water vapour and ice crystals from its South Pole and this is thought to come from an underground sea," he says.
Fortes says methanol monohydrate, which remains a liquid down to temperatures of -103°C, could be acting as a type of 'anti-freeze', keeping the undersurface water liquid.
In a commentary appearing in the same issue of Science, Professor Joseph Grima and colleagues from the University of Malta, believe this new insight into methanol monohydrate could have other implications for astronomy.
"Composites made from NTE (negative thermal expanding) and conventional materials can be designed to exhibit a zero thermal expansion coefficient for use as mirror substrates in various telescope and satellite applications," they write.
"Similarly, negative compressibility materials can be used in applications requiring extremely sensitive pressure detectors."