NASA probe to collect comet dust

A NASA spacecraft will fly through the tail of a comet on Friday, the climax of its five-year mission.

Scientists at NASA's Jet Propulsion Laboratory said the probe is on track to pass within 300 kilometres of the comet Wild 2's "tail" of gas and debris.

The bookcase-sized probe, called Stardust, is expected to take photographs, collect data and scoop up dust particles.

It will be the first time scientists have collected samples from a comet and brought them back to Earth for analysis.

"We are literally collecting preserved samples of the building blocks of our solar system and our Earth and even ourselves," said Donald Brownlee, a University of Washington astronomer who is the mission's chief scientist.

Shimmering gas boils from a comet's surface as it is warmed by the sun.

Scientists want to study the pristine particles, which were preserved for 4.6 billion years in the cold of space.

Stardust has two specially designed bumpers to protect its solar panels and instruments from the debris.

The spacecraft's "catcher's mitt" will snag the tiny debris as it passes through the comet at about 22,000 kilometres per hour.

Since Stardust was launched in 1999, it has orbited the sun three times en route to comet Wild 2. Astronomer Paul Wild discovered the dusty celestial wanderer in 1978.

Stardust will return the mitt and its extraterrestrial contents in January 2006.