Tuesday, January 3, 2012

Physics & Math

Nobel prizewinning quasicrystal fell from space

It came from outer space <i>(Image: Luca Bindi and Paul Steinhardt)</i>
It came from outer space (Image: Luca Bindi and Paul Steinhardt)
A Nobel prizewinning crystal has just got alien status. It now seems that the only known sample of a naturally occurring quasicrystal fell from space, changing our understanding of the conditions needed for these curious structures to form.
Quasicrystals are orderly, like conventional crystals, but have a more complex form of symmetry. Patterns echoing this symmetry have been used in art for centuries but materials with this kind of order on the atomic scale were not discovered until the 1980s.
Their discovery, in a lab-made material composed of metallic elements including aluminium and manganese, garnered Daniel Shechtman of the Technion Israel Institute of Technology in Haifa last year's Nobel prize in chemistry.
Now Paul Steinhardt of Princeton University and colleagues have evidence that the only known naturally occurring quasicrystal sample, found in a rock from the Koryak mountains in eastern Russia, is part of a meteorite.

Nutty conditions

Steinhardt suspected the rock might be a meteorite when a team that he led discovered the natural quasicrystal sample in 2009. But other researchers, including meteorite expert Glenn MacPherson of the Smithsonian Institution of Washington DC, were sceptical.
Now Steinhardt and members of the 2009 team have joined forces with MacPherson to perform a new analysis of the rock, uncovering evidence that has finally convinced MacPherson.
In a paper that the pair and their teams wrote together, the researchers say the rock has experienced the extreme pressures and temperatures typical of the high-speed collisions that produce meteoroids in the asteroid belt. In addition, the relative abundances of different oxygen isotopes in the rock matched those of other meteorites rather than the isotope levels of rocks from Earth.
It is still not clear exactly how quasicrystals form in nature. Laboratory specimens are made by depositing metallic vapour of a carefully controlled composition in a vacuum chamber. The new discovery that that they can form in space too, where the environment is more variable, suggests the crystals can be produced in a wider variety of conditions. "Nature managed to do it under conditions we would have thought completely nuts," says Steinhardt.


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