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For those who have always believed in life on other planets, the discovery of an amino acid in space is probably no big deal. Hardened sceptics may simply find the announcement hard to swallow. But the fact remains that American radio astronomers have found this fundamental building block of life in a dense cloud of interstellar gas and dust near the centre of our Galaxy.

The amino acid was found in a star-forming region, about a light year across, where the stars have not yet ‘switched on’, says Lewis Snyder of the University of Illinois at Urbana-Champaign. His group has detected spectral lines characteristic of many large molecules in the cloud, called Sagittarius B2, as well as glycine, the simplest of the amino acids which link up to form proteins.

Two of his students, Yanti Miao and Yi-Jehng Kuan, reported the findings last week at a meeting of the American Astronomical Society in Minneapolis.

The discovery is important because it may explain crucial early steps in the origin of life. Most theories assume that chemical reactions on the early Earth produced increasingly complex molecules, and eventually generated living things. However, scientists have been puzzled by the apparent speed with which life appeared, only a few hundred million years after the planet’s crust solidified.

Over the past few years, astronomers have in fact discovered more than 100 molecules in space. Some have up to 13 atoms, making them more complex than glycine, which has only 10 atoms. Some people claim to have detected even bigger and more complex molecules further along the road to life, but their observations have not been confirmed. The discovery of glycine in space ‘shows that the chemistry of prebiotic early Earth is the common chemistry of the Galaxy’, says Snyder.

The idea that space contains many complex molecules was heretical when the astrophysicist Fred Hoyle and astronomer Chandra Wickramasinghe advanced it in the 1970s. Now the theory is widely accepted. ‘It’s been a long hard struggle,’ says Hoyle. ‘In the 1950s nobody would hear even a word that there could be even simple molecules in space. It was all atomic hydrogen or ionised hydrogen. You were just a maverick if you suggested molecules in space.’ Astronomers have yet to verify another of Hoyle’s more controversial suggestions, that primitive life may have originated in space and then seeded the Earth and other planets.

Wickramasinghe, who is based at the University of Wales at Cardiff, says that the discovery was ‘no surprise at all’. He believes it is only a matter of time before other amino acids, together with nucleotide bases, the components of nucleic acids that make up genetic material, are found in space. ‘This is just the tip of the iceberg,’ he says. ‘I would fully expect a vast array of life molecules to be discovered in space, and then there would be no doubt as to where terrestrial life began.’

In the past 70 years, astronomers have been puzzled by about a hundred ‘diffuse’ absorption features in the visible and near-infrared spectra of stars. Although large molecules produce such features, they cannot be identified from them. ‘In the next decade, I expect us to discover many of the molecules responsible,’ says Wickramasinghe. But identifying really complex biological molecules in space, such as proteins, will be very difficult, he says. ‘Their spectra will be complex, making identification ambiguous.’

The abundance of complex molecules in space may also indicate that life is widespread in the Galaxy. The intense radiation emitted by young stars and the gravitational energy released during the formation of the planets would probably destroy most molecules exposed to them. However, Snyder says that even if a planet starts off barren, asteroids, comets and interplanetary dust could carry the initial molecular building blocks of life to its surface. In fact, there have been disputed claims that amino acids are present in some meteorites. They would give an early start to the processes which give rise to living things.

Snyder’s evidence comes from three years of painstaking observations at frequencies of 85 to 115 gigahertz, the region where large molecules have characteristic spectral lines, with the Berkeley-Illinois-Maryland Array of radio dishes in northern California. He cautions that the results are not definitive, and he wants to make another run of observations to check for other spectral lines from glycine. However, among the phenomenal amount of raw data he gathered from the same cloud he has also found 25 other lines of ‘large floppy molecules’, including ethyl cyanide, vinyl cyanide, and methyl formate. The detection of these molecules makes the presence of glycine, which is of similar size and complexity, seem credible.