Tau Ceti system, Asteroid Alley - an inhospitable neighbour


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UK astronomers studying the Tau Ceti system have discovered that it contains ten times as much material in the form of asteroids and comets as our own solar system. Their discovery, being published in Monthly Notices of the Royal Astronomical Society, suggests that even though Tau Ceti is the nearest Sun-like star, any planets that may orbit it would not support life as we know it due to the inevitable large number of devastating collisions. It also suggests that the tranquil space environment around the Earth may be more unusual than previously realised.

Tau Ceti, only 12 light years away, is the nearest Sun-like star and is easily visible without a telescope. It is the first star to be found to have a disk of dust and comets around it similar in size and shape to the disk of comets and asteroids that orbits the Sun. But the similarity ends there explains Jane Greaves, Royal Astronomical Society Norman Lockyer Fellow and lead scientist: "Tau Ceti has more than ten times the number of comets and asteroids that there are in our Solar System. We don't yet know whether there are any planets orbiting Tau Ceti, but if there are, it is likely that they will experience constant bombardment from asteroids of the kind that is believed to have wiped out the dinosaurs. It is likely that with so many large impacts life would not have the opportunity to evolve."

The discovery means that scientists are going to have to rethink where they look for civilisations outside our Solar System. Jane Greaves continues "We will have to look for stars which are even more like the Sun, in other words, ones which have only a small number of comets and asteroids. It may be that hostile systems like Tau Ceti are just as common as suitable ones like the Sun."

The reason for the larger number of comets orbiting Tau Ceti is not fully understood, explains Mark Wyatt, another member of the team: "It could be that our Sun passed relatively close to another star at some point in its history and that the close encounter stripped most of the comets and asteroids from around the Sun."

The new results are based on observations taken with the world's most sensitive submillimetre camera, SCUBA. The camera, built by the Royal Observatory, Edinburgh, is operated on the James Clerk Maxwell Telescope in Hawaii. The SCUBA image shows a disk of very cold dust (-210 C) in orbit around the star. The dust is produced by collisions between larger comets and asteroids that break them down into smaller and smaller pieces.

UK participation in the James Clerk Maxwell Telescope is provided by the Particle Physics and Astronomy Research Council (PPARC). Professor Ian Halliday, PPARC Chief Executive said "SCUBA continues to unveil the mysteries of planetary systems, in this case the "asteroid alley" that is Tau Ceti; - clearly a place you would not wish to be."

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