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Burn ignition!
Mission control erupts in applause as communications from Cassini confirm the orbit insertion burn has begun. (60sec file)
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Burn completed
Signals from Cassini announce the conclusion of the Saturn orbit insertion burn, confirming the spacecraft has arrived at the ringed planet. (2min 15sec file)
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Post-arrival briefing
Mission officials hold a post-orbit insertion burn news conference at 1 a.m. EDT July 1 to discuss Cassini's successful arrival at Saturn. (25min 27sec file)
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International cooperation
Officials from the U.S., European and Italian space agencies discuss the international cooperation in the Cassini mission and future exploration projects during this news conference from 2 p.m. EDT June 30. (19min 35sec file)
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'Ring-side' chat
This informal "ring-side chat" from 5 p.m. EDT June 30 discusses the Cassini mission to Saturn and the future of space exploration. (49min 20sec file)
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Tranquil environment around Earth may be unusual
Posted: July 5, 2004

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.

For any planets orbiting Tau Ceti, the skies will be criss-crossed with comets and meteors will frequently strike the surface. Credit: David A. Hardy
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 BAC) 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."

Publication of the result coincides with an exhibit "Hunting for Planets in Stardust" at the Royal Society Summer Exhibition by the same science team from the UK Astronomy Technology Centre in Edinburgh and the University of St Andrews.

Tau Ceti is in the constellation Cetus. Although it is visible without a telescope, at this time of year it rises in the South East at about 3am - just before the sun, so is very hard to spot.

The Particle Physics and Astronomy Research Council (PPARC) is the UK's strategic science investment agency. It funds research, education and public understanding in four broad areas of science - particle physics, astronomy, particle astrophysics and space science.

PPARC is government funded and provides research grants and studentships to scientists in British universities, gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Organisation for Nuclear Research, CERN, the European Southern Observatory and the European Space Agency. It also contributes money for the UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh and the MERLIN/VLBI National Facility.