Astronomers may have shown how microbes from Earth could be spread throughout the galaxy taking life to other worlds. Scientists at Armagh Observatory and Cardiff University say bacteria could get into space on rocks blasted off the planet by an asteroid or comet impact. Their calculations then indicate the microbes would eventually leak out of our Solar System to seed other regions. The work is reported in two independent papers published in the Monthly Notices of the Royal Astronomical Society. The implication of the papers is that life could be widespread throughout the galaxy and may not have originated on our planet. The research advances the case for modern-day panspermia - the controversial idea that life started elsewhere in space and came to Earth when it was young. Dr Max Wallis and Professor Chandra Wickramasinghe of Cardiff University calculate how debris from Earth, thrown into space as a result of a giant impact, would become incorporated in the frozen outer layers of comets. Eventually, after hundreds of millions of years, some of these comets would reach the Edgeworth-Kuiper Belt - a region inhabited by small worlds made of rock and ice.

Because comets gradually leak into interstellar space from this region, some would eventually reach clouds of gas and dust that are new planetary systems in formation. In these systems, the trapped microbes would be liberated and, if the conditions were right, introduce life on to the surfaces of primitive planets. Wallis and Wickramasinghe are encouraged in their belief that microbes can survive on such a journey for hundreds of millions, if not billions, of years, by recent discoveries of microbes that have survived for similar periods encased in rock in the Earth.

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