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Last Updated: Thursday, 22 December 2005, 11:21 GMT
Stardust targets lightning return
By Jonathan Amos
BBC News science reporter

Artist's rendering of Stardust recovery, Nasa
Stardust will touch down in the Utah desert
The US space agency (Nasa) is confident it can land samples from a comet back on Earth next month without mishap.

The Stardust mission grabbed dusty debris from around Comet Wild 2 almost two years ago and will return its precious cargo on 15 January.

A sample capsule will enter the Earth's atmosphere faster than any previous manmade object and then attempt to make a soft landing in the Utah desert.

Nasa scientists and engineers believe their parachute system will cope.

They are mindful of the problems that afflicted a previous sampling probe called Genesis, which crashed to Earth last year when its parachute system failed to open.

The Stardust team told reporters on Wednesday they were positive there would be no repeat performance - but were prepared and had trained for all eventualities.

"We took the lessons from Genesis and we went through a very rigorous and extensive process looking at the Stardust return capsule," explained Ed Hirst, mission system manager on Stardust.

"There is always some residual risk that something could go wrong on return but we think the probability of that is very low at the moment."

Tom Duxbury, the project manager, added: "Our return capsule is quite small but extremely rugged. In the event that a chute doesn't open or we have a hard landing, we know we can finish our science opportunity."

Amazing view

The Stardust probe is coming to the end of a seven-year, 4.8-billion-km (2.9 billion miles) journey around the Solar System - the highlight of which was a close encounter with Comet 81P/Wild 2 on Friday 2 January, 2004.

During the flyby, the spacecraft snapped more than 70 images and gathered a mass of data which scientists continue to scrutinise.

Stardust returned 72 images from its encounter

Its pictures were a revelation - the best close-up view at that time of a cometary nucleus ever obtained.

The images revealed a pockmarked "flying mountain" alive with jets of gas and dust that billowed in the solar wind.

"We were stunned when we got to the comet and saw incredible features - steep cliffs, overhanging cliffs, spires and many features which, oddly enough, we had never been seen on other Solar System bodies," recalled principal investigator Don Brownlee.

Stardust flew through the comet's outflow with a tennis-racket-like contraption, collecting particles in a material called aerogel, a low-density substance that is 99.8% empty space.

The samples were safely stowed in a capsule and it is this container which the main Stardust spacecraft is now about to jettison on its return flight past Earth.

Space 'library'

The 46kg (100lb) capsule will strike Earth's atmosphere at nearly 13km/s (eight miles/s) - more than 10 times faster than a speeding bullet. It will produce a huge streak of light in the sky over the American northwest as it slows in the thick air.

A parachute system should then deploy to bring the container to a gentle touchdown at the US Air Force Utah Test and Training Range - at 0312 local time (1012GMT).

Stardust's mission: How Nasa's probe collected comet dust and will return it to Earth

Researchers expect their studies of the samples grabbed 389 million km from Earth to give new insights into the construction of comets and the earliest history of the Solar System.

Chemical and physical information locked within the particles could be the record of the formation of the planets and the materials from which they were made.

"Our mission is called Stardust, in part because we believe some of the particles in the comet will be older than our Sun and planets, and formed around other stars," Dr Brownlee said.

"We're using the comet as a sort of library. It scooped up the building blocks of the Solar System, preserved them far from the Sun at low temperatures for four and a half billion years, and has now dumped them; we grabbed them two years ago and they're landing in the desert in just a couple of weeks."

See how Nasa intends to bring the Stardust samples home

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