An international team of astronomers has found a possible explanation for why the amino acids in all living creatures are "left-handed", and why all sugars are right-handed - a mystery that has puzzled scientists for 150 years. Molecules with the same chemical composition can exist in two different forms, each the mirror image of the other. When molecules are created in the laboratory, left- and right-handed forms are created in equal number. Now astronomers using the Anglo-Australian Telescope have found evidence that left-handedness was imprinted in organic molecules in interstellar space before the formation of the Solar System (Jeremy Bailey et al 1998 Science 281 672).
Fred Hoyle was the first to suggest that organic molecules developed in outer space and then fell to the earth, but it was not until the discovery of large quantities of left-handed amino acids in a meteorite last year that biologists seriously started to think about an extraterrestrial origin for the left-handedness of amino acids. If an equal amount of left- and right-handed molecules are bombarded by circularly polarized ultraviolet light, the molecules would take on the same orientation of the light. Although circularly polarized light comes in left- and right-handed version, it is rarely encountered in nature. The Sun, for example, emits unpolarized light.
Bailey et al. observed part of the Orion nebula called OMC-1, a region containing many organic molecules in conditions similar to when the solar system formed. They found that infrared light in this region had been circularly polarised by dust grains. According to their calculations, a similar polarization effect could occur at ultraviolet wavelengths. The observations suggest that the suitability of the Earth for life may be as much a consequence of the environment in which the solar system was formed as of the local conditions on the early Earth.
