Stardust sweeps up interstellar dust

Drawing of the $200 million Stardust mission craft

(CNN) -- Stardust, the first spacecraft designed to return space samples from beyond the moon, began harvesting interstellar dust this week from beyond the solar system.

The NASA robot ship, halfway into a seven-year journey, opened its waffle-shaped particle collector to catch the tiny grains, which permeate our galaxy.

"If you look at the Milky Way on a dark night you may see a black band stretching along the center," said Stardust mission scientist Don Brownlee.

"The band is interstellar dust blocking the light from distant stars. These are the particles that Stardust will be collecting," said Brownlee, an astronomy professor at the University of Washington in Seattle.

Stardust's collector contains a transparent, ultralight glass foam called aerogel, the world's lightest solid, to snag samples from a river of interstellar particles beyond the orbit of Mars.

The refrigerator-sized craft will remain in the dust stream until December. NASA scientists hope the gel will catch dozens of the fast-moving grains.

This is a sample of aerogel, which is made mostly of air and almost as light.

The dust job is a precursor to the $200 million mission's main event, snatching microscopic debris samples from comet Wild 2 during a close encounter in 2005.

Stardust has overcome numerous difficulties since its 1999 launch, including blurry vision in its navigation camera and a mysterious case of excessive thruster firing.

The probe should return to Earth with its cosmic samples in January 2006, landing via parachute in the Utah desert.

By studying what Stardust returns, scientists think they could learn if comets or interstellar dust provided the water or organic material necessary to form life.

Comets, possibly the oldest bodies in the solar system, could contain a record of the original material that formed the sun and planets 4.5 billion years ago.

Interstellar particles consist of most of the known elements and include complex carbon structures. Their exact origin remains a mystery but scientists think they are linked to young stars.