Space probe flies into comet's tail in search of icy evidence

A spacecraft that has travelled two billion miles through space yesterday flew into the tail of a comet in the hope of bringing a sample back to Earth. The Stardust skimmed past comet Wild 2 with the aim of capturing some of the ice and dust that flows out in a long tail or "coma" from the nucleus of the comet.

A spacecraft that has travelled two billion miles through space yesterday flew into the tail of a comet in the hope of bringing a sample back to Earth. The Stardust skimmed past comet Wild 2 with the aim of capturing some of the ice and dust that flows out in a long tail or "coma" from the nucleus of the comet.

Tom Duxbury, the Stardust programme manager at Nasa's Jet Propulsion Laboratory in Pasedena, California, said this will be the first time anyone has tried to bring back fragments of comet material for analysis.

"Just like in Star Trek we have our shields up. The spacecraft has entered Wild 2's coma, which means at any time we could run into a cometary particle," Dr Duxbury said. Stardust's protective shields are needed because it is travelling at 3.8 miles per second and a collision with even the smallest rock could spell disaster for the spacecraft, he said.

The shielding system includes two bumpers at the front, which protect Stardust's delicate solar panels, and another shield protecting the main body. Each shield is built around panels designed to disperse particles as they collide.

A special particle-catcher shaped like a tennis racket and filled with a lightweight material called aerogel is designed to stick out from the Stardust spacecraft to collect samples of material which will be brought back to Earth.

The aerogel is made of pure silicon dioxide ­ like sand and glass ­ but is a thousand times less dense because it is 99.9 per cent air, allowing it to capture tiny cometary particles without damaging them. The passage through the most intensive rain of particles is expected to last about eight minutes.

Don Brownlee of the University of Washington, the principal investigator on the mission, said that the project sets new goals in exploring the nature of the material that makes up comets.

"In recent decades, spacecraft have passed fairly close to comets and provided us with excellent data. Stardust, however, marks the first time that we have collected samples from a comet and brought them back to Earth for study. The samples we will collect are extremely small and can only be adequately studied in laboratories with sophisticated analytical instruments."

In addition to catching particles, the spacecraft has a sophisticated camera that will be active during the flyby and should be able to beam back images of the comet's nucleus taken from within its tail.

After the samples are collected, the collecting instrument is designed to fold down into a return capsule which will close like a clamshell to make sure that it is protected during its soft landing on Earth.

Scientists hope that studying the cometary material will provide valuable insights into the process whereby the Solar System was formed.

Astronomers believe comets are "builders' rubble" left over from the creation of the planets more than four billion years ago. Stardust is scheduled to return to Earth in January 2006.