Stardust capsule returns to Earth
By Helen Briggs
BBC News science reporter
news.bbc.co.uk
Watch the landing
A capsule containing dust collected from a comet and stars has landed on Earth after a seven-year space mission.
The US probe Stardust released the capsule as it flew past Earth after a 3 billion-mile (4.7 billion km) trip.
The capsule plunged through the atmosphere and touched down in the Utah desert at 0312 (1012 GMT).
Scientists believe the pristine particles snatched from a comet and interstellar space will give insights into the origins of the Solar System.
It is the first time in history that a space mission has brought back such material.
Fiery descent
The Stardust spacecraft released the 101lb (45kg) capsule at 0557 GMT as it looped past the Earth on its return from deep space.
The capsule was visible as a dot in the sky
Mission controllers at the US space agency Nasa Jet Propulsion Laboratory in Pasadena, California, clapped and cheered as the capsule began its plunge to Earth.
Four hours after leaving the probe, the capsule entered the Earth's atmosphere 125km (410,000ft) over the Pacific Ocean.
It reached speeds of 46,660kph (29,000mph) - the fastest re-entry of any manmade probe - and was visible from parts of the American northwest as a streak of light in the sky.
At about 32km altitude (105,000 feet), the capsule released a small parachute to slow its descent.
The main parachute opened at about 3km (10,000ft), and brought the capsule down to land on a military base southwest of Salt Lake City.
"All stations, we have touchdown," an announcer declared to a jubilant control room.
First analysis
The capsule was located by helicopter almost an hour after the landing. It was then flown to a nearby army building for preliminary analysis.
In the next few days, it will be transported to a special lab at Nasa's Johnson Space Center in Houston, Texas, where scientists will get their first chance to examine the precious contents.
"I'm very confident we will have samples in there that are the first returned from beyond the Moon," former Stardust project manager, Ken Atkins, told the BBC News website.
"It is magnificent to see something that we saw leave the planet on 7 February 1999 return to the planet here on 15 January 2006."
The main probe was sent into permanent orbit around the Sun shortly after its cargo was jettisoned.
Close encounter
The highlight of Stardust's seven-year mission was its close encounter with Comet Wild 2 in January 2004.
Stardust returned 72 images from its encounter
More details
It swept up particles from the frozen body of ice and dust, as it flew to within 240km (149 miles).
As part of its trip, the probe also captured a sprinkling of dust that would have originated in distant stars.
The comet and dust molecules were trapped in cells filled with a specially-developed ultra-light foam called aerogel.
The capsule is believed to contain about a million particles of comet and interstellar dust leftover from the birth of the Solar System.
The microscopic particles represent the first solid material returned to Earth from an extraterrestrial body since 1976, when the unmanned Soviet Luna 24 mission brought back moon rocks and soil.
Technical challenge
Hundreds of scientists around the world are waiting to analyse the samples in detail, including researchers at the UK's Open University.
Stardust could provide a new window into the distant past
Dr Simon Green
Monica Grady of the Planetary and Space Science Research Institute (PSSRI) said the tiny particles from Stardust would be the most scientifically exciting and technically challenging material they had ever had the opportunity to study.
"Imagine trying to pick up a grain that is less than a hundredth of the size of the full stop at the end of this sentence," she said.
"It is amazing to think that such minute specks of dust can carry within them so much information about the origin of stars and planets."
Time capsules
Comets are thought to be cosmic "time capsules", containing material unchanged since the formation of the Sun and planets.
Stardust's mission: How Nasa's probe collected comet dust and will return it to Earth
More details
Some even think they may have seeded Earth with the chemical building blocks required for life.
"Stardust could provide a new window into the distant past," said Dr Simon Green of the PSSRI.
"Because these particles have come from inside a comet we know that essentially the particles haven't been heated since they became part of the comet, because the comet is made of ice," he told the BBC News website.
"That means that they contain information about the conditions that were present when they were incorporated into the comet.
"That time was four-and-a-half thousand million years ago, back when the Solar System formed, so what we hope to know from these particles is essentially what the Solar System looked like at that time, and essentially what we're all made of."
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