Nasa takes off in search of stardust

AN AMBITIOUS attempt to capture the floating stardust of interstellar space will begin this weekend with the launch of the first spacecraft to bring back extraterrestrial material to Earth since the Apollo rockets of the early Seventies.

The Stardust spacecraft - named after the lyrics of "Woodstock" sung by Joni Mitchell - will chase a distant comet and capture the minute particles of material in its tail. It will also collect interstellar dust from deep space.

Scientists hope to study the interstellar particles and cometary dust when they are returned to Earth in seven years' time to learn more about the evolution of the solar system and how life began on Earth.

Stardust, an international mission led by the American National Aeronautics and Space Administration (Nasa), is scheduled for lift-off on Saturday and will make contact with comet Wild-2 (pronounced "Vilt-2") in January 2004.

The spacecraft will fly by the comet at a speed of 14,000mph and use an instrument shaped like a tennis racket and coated in aerogel, a material known as "frozen smoke" because it is the lightest man-made solid, to capture the delicate dust.

Tony McDonnell, professor of space physics at the University of Kent at Canterbury, which has helped to build a set of microphones to listen to the sound of the stardust being caught, said the dust has been preserved in a pristine state since the solar system was created about 4.7 billion years ago. "We've come from a similar cloud of interstellar dust and gas that condensed to form the planets. The cometary material may have brought the life-sustaining elements - the carbon and water-based chemicals - to Earth," he said.

Donald Brownlee, professor of astronomy at the University of Washington in Seattle, who devised the idea for the mission in 1980, said bringing stardust back to Earth for analysis could help to explain the evolution of life. "The building blocks of life have long been thought to have come from further out in the solar system, out further away from the Sun, and these would be materials from asteroids and comets," he said.

"People have long suspected that comets play a role in the origin of life. No one really knows this because no one knows how life began.

"But we do know that comets are the most carbon-rich materials in the solar system, and we know they're full of organic compounds and they fall on the Earth all the time."

The cometary particles that are found on Earth have suffered too much damage during their journey through the atmosphere to be of much use in learning about the state of matter at the beginning of time. Comet Wild- 2 is perfect to search for the best-preserved material because it has rarely passed near to the Sun and so has not suffered the damaging effects of solar radiation, Professor Brownlee said.

"There hasn't been time enough for the Sun's heat to destroy the characteristics of particles that have been preserved in the cryogenic deep freeze of space for billions of years."

The stardust spacecraft will be the first mission since Apollo 17 in 1972 to return extra- terrestrial samples from space, and the first to bring back material from beyond the Moon.

The stellar dust caught up in a comet's tail is the only known physical clue to the events that led to the formation of planets and the evolution of life, Professor Brownlee said. "You can at least look at what the starting materials were. So that's what Stardust is going to do."

Professor Brownlee said the lyrics of "Woodstock" - "We are stardust, we are golden, we are 2 billion-year-old carbon" - are apt for the mission.

"Many of the carbon atoms in our bodies were in comets early in the history of the solar system. So one of the bylines of the Stardust mission is that we are stardust. Our bodies are actually made of stardust," he said.

However, despite the affiliation to "Woodstock", Nasa plans to play Hoagy Carmichael's "Stardust" for the countdown.