Space probe on comet quest

The rocket carrying Stardust lifted off under clear skies, achieving an elliptical orbit around the Sun around 26 minutes later.

The launch had been delayed from Saturday due to a slight power fluctuation in a radar beacon used for tracking the spacecraft's Boeing Delta II rocket after lift-off.

Stardust is intended to cross paths with the Comet Wild-2 in January 2004, some 285m kilometres (178m miles) from Earth.

A comet is a flying mountain of rock, ice and frozen gasses.

If it nears the Sun, it begins to warm and the so-called nucleus - Wild-2's is estimated to be 9.5 km (6 miles) wide - becomes a bubbling mass of geysers and jets erupting from its surface.

The comet becomes enveloped in a cloud of dust and gas, some of which trails away from it, pushed by the pressure of sunlight. These are the comet's tails.

As the comet sweeps past the probe, Stardust will collect microscopic particles of cometary debris.

Once Stardust has collected the samples, it will return them to Earth in 2006 for a parachute landing in the Utah Salt Flats.

Scientists believe the materials released by the comet have been frozen for billions of years and could provide a unique glimpse into the origins of life on Earth and, perhaps, elsewhere in the Solar System.

The last time extra-terrestrial samples were returned to Earth was in 1976 when the Soviet Lunar 24 mission brought back 170g of lunar material to the Earth.