A BIZARRE form of matter that might be floating 90 kilometres above Earth鈥檚 surface could help explain one of life鈥檚 enduring mysteries: why are the building blocks of the living world mostly left-handed?
Many biomolecules, including proteins and amino acids, are 鈥渃hiral鈥�: they can have two distinct 鈥渉anded鈥� forms which are mirror images of one another. For some reason, life on Earth shows a preference for left-handed proteins and amino acids, but no one knows quite why.
What we do know is that exposing a mixture of equal parts left and right-handed molecules to circularly polarised radiation will destroy one while leaving the other intact. Now , a chemist at the University of Gothenburg, Sweden, thinks circularly polarised light could be generated naturally by a rare form of matter called .
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First hypothesised in the 1930s by the physicist Enrico Fermi, a Rydberg atom is typically an alkali metal, such as sodium, in which the outer electron orbits an unusually long way out from the nucleus. Rydberg matter is an alkali metal cloud formed from clusters of these atoms.
When Holmlid created such a cloud in a vacuum chamber in his lab and shone a linearly polarised laser through it, he found that 50 per cent of the light that emerged was circularly polarised (Astrobiology, ). He suggests that something similar could be happening in a atoms that exists at an altitude of 90 kilometres above Earth. If so, it could be the origin of light that gives biomolecules the handedness that we see.
鈥淐ircularly polarised light could be generated in a layer of sodium atoms 90 kilometres above Earth鈥�
Holmlid says this is a more likely explanation than some that have been offered in the past, such as radiation from neutron stars. He admits, however, that there are a lot of 鈥渕aybes鈥� with his scenario. For instance, we don鈥檛 know if the sodium layer above Earth does in fact consist of Rydberg matter, which is difficult to detect outside a lab. There is some evidence to suggest that such clouds exist in the atmosphere of Mercury.
The idea is 鈥渁 totally new thing鈥�, says , an astrobiologist at NASA鈥檚 Ames Research Center at Moffett Field, California. He cautions, however, that the work only roughly approximates conditions in space or the upper atmosphere. Still, Bernstein says he finds the idea exciting. 鈥淭hey鈥檝e shown that, in principle, this could happen,鈥� he says.