After a seven-year journey, the US space probe "Stardust" is scheduled to deliver to Earth on Sunday samples of rare dust it has collected from stars and comets that scientists believe could offer vital clues about the solar system's origins.

A capsule weighing 46 kilograms and carrying a teaspoonful of space dust is expected to land in a Utah desert at 1012 GMT on Sunday after flying 4.63 billion kilometres in space, or 10,000 times more than the distance separating Earth from the Moon.

The samples were collected during the first attempt to gather beyond the Moon space particles that date back to before the solar system was born, or about 4.5 billion years ago.

It also follows the 1972 mission of Apollo 17 that allowed US astronauts to bring Moon rocks back to Earth.

And it returns to Earth as NASA prepares to launch its New Horizons probe on Tuesday in a mission to Pluto.

"Locked within the cometary particles is unique chemical and physical information that could be the record of the formation of the planets and the materials from which they were made," said Don Brownlee, Stardust principal investigator at the University of Washington, Seattle.

Launched in 1999, the 385-kilogram probe, circled the Sun twice and then flew in January 2002 by comet Wild 2, which was located at the time next to Jupiter.

During the hazardous traverse, the spacecraft first deployed a shield to protect itself from gases and space dust contained in the halo of the comet.

It then flew within 240 kilometres of Wild 2, catching samples of comet particles and scoring detailed pictures of Wild 2's pock-marked surface.

The 72 pictures of Wild 2 taken by the probe show its rugged surface, including craters as well as about 20 "geysers" spewing gas and dust.

During 195 days of the flight, NASA engineers used a collector to gather interstellar dust that will allow scientists to study the make-up of stars.

The special collector contains aerogel, a unique substance that can trap the particles and store the precious cargo safely until it's returned to Earth.

Mary Cleave, associate administrator for NASA's Science Mission Directorate, said the load Stardust will return to Earth could help space explorers on many future missions.

"Comets are some of the most informative occupants of the solar system," she said. "The more we can learn from science exploration missions like Stardust, the more we can prepare for human exploration to the moon, Mars and beyond."

If everything goes according to plan, on Sunday at 0557 GMT, Stardust will release its return capsule.

About four hours later, the capsule will enter Earth's atmosphere 125 kilometres over the Pacific Ocean.

The capsule will release a parachute at approximately 32 kilometres.

Once the capsule has descended to about three kilometres, its main parachute will deploy.

The capsule is scheduled to land at a military base in Utah at 1012 GMT.

After the capsule lands, a helicopter crew will fly it to the US Army Dugway Proving Ground, Utah, for initial processing.

If the weather is inclement and helicopters cannot fly, special off-road vehicles will retrieve the capsule and return it to Dugway.

The samples will be moved to a special laboratory at NASA's Johnson Space Centre in Houston, Texas, where they will be preserved and studied.

The analysis could take scientists as long as 10 years. The work, according to one scientist, could be compared to finding 45 ants on a football field, studying five square centimetres of earth at a time.

To help the researchers, the University of California, Berkeley, has launched a drive to recruit 30,000 volunteer students, who will have access to a powerful microscope via the Internet.