Computer users are being invited to join the hunt for minute grains of star dust that a NASA spacecraft should return to Earth this weekend.

The Stardust spacecraft should land in Utah early Saturday, carrying in its hold a sprinkling of grains of interstellar dust scooped up during its seven-year mission.

Researchers are seeking the public's help in pinpointing the submicroscopic bits of dust, leftovers from stellar explosions perhaps millions of years old, in photos they plan to place on the Web.

Researchers should begin posting in March the first of an anticipated 1.5 million microscopic images of the collector plate that Stardust used to snag the dust grains while it orbited our sun.

The hope is that keen-eyed participants in the Stardust@home project can expedite the search for the estimated 45 interstellar dust grains Stardust is expected to have captured by helping sift through the hundreds of thousands of pictures of the roughly square-foot collector plate.

Users will have to prove their mettle before they are allowed to participate in the search.

That includes undergoing some Web-based training, passing a test and registering before being allowed to use the virtual "microscope," the University of California, Berkeley researchers behind the project said.

They unveiled the project Tuesday at the 207th meeting of the American Astronomical Society. They expect they will need 30,000 person hours to comb through all the images at least four times.

Each picture will cover an area smaller than a grain of salt. The goal is to identify tell-tale tracks left behind in the collector by the grains. Once confirmed, the researchers will target that location in their attempts to extract the nearly invisible grains for detailed study.

Scientists hope the grains will give insight into the internal processes of distant stars, including how they generate elements like carbon and oxygen that are necessary for life.

The project is similar to SETI@home, which created a virtual supercomputer through Internet-connected PCs to search for signs of extraterrestrial life.