Extraterrestrial clue to left-handedness

ASTRONOMERS HAVE found evidence to support the controversial theory that the building blocks of life originated in outer space and were carried to Earth on comets about 4 billion years ago.

Scientists have discovered a phenomenon in the region of the Giant Nebula, a massive cloud of gas in the Orion constellation, which could explain why biological molecules on Earth are all ''left handed''.

Organic molecules necessary for life, such as amino acids, can exist in one of two forms, which are both right and left-handed mirror images of each other. But in practice they only occur in the left-handed form.

For the past 150 years, scientists have found it difficult to explain why the buildings blocks of life should all be left-handed when it is just as easy to make the right-handed mirror image.

One possible explanation for the origin of biological left-handedness is that it had an extraterrestrial source which meant that the earliest life forms began using left-handed molecules and, once they started, could never use the right-handed forms.

Early support for the idea came with the discovery of an abundance of left-handed amino acids in a meteorite which fell in 1969 in the Murchison area near Victoria in New South Wales, Australia.

Scientists also found that the Murchison meteorite was about 4.5 billion years old, confirming that left-handedness in space predated the origin of life on Earth which occurred about 3.8 billion years ago.

This suggested that the organic molecules necessary for early lifeforms on Earth could have come from space, riding on the back of comets or meteors during the period when the early world was heavily bombarded.

Another feature of left-right symmetry in biological molecules was discovered in the 1930s. Scientists found that a type of light, called circularised polarised light, which can rotate either clockwise or anti-clockwise, can selectively destroy either right-handed or left-handed molecules depending on the direction the light is rotating.

A team of researchers, which included Professor James Hough of the University of Hertfordshire, report in the current issue of the journal Science that they have now found a region of circularised polarised infrared light in a region of the Giant Nebula called the Orion Molecular Cloud 1.

''We know that new stars are being formed here, and we also know that organic molecules are present. This region may well be similar to the region in which our own solar system formed,'' Professor Hough said.

''The circular polarised light in the region we investigated could imprint a preferred handedness in any organic molecules in the region, including those in a cloud beginning to collapse to form a star and its planets,'' he said.

''These results therefore suggest that the suitability of our planet for life may be as much a consequence of the environment in which our solar system formed as of the local conditions on the early Earth.''

Professor Hough said that although the discovery falls short of proof that life's building blocks came from outer space. ''We believe it's the most plausible explanation to date.''

The astronomers made their discovery using the Anglo-Australian Telescope near Coobabaraban in New South Wales and using instruments made at Hertfordshire University.