Science & Environment

Japanese Hayabusa asteroid mission comes home

A capsule thought to contain the first samples grabbed from the surface of an asteroid has returned to Earth.

The Japanese Hayabusa container hit the top of the atmosphere just after 1350 GMT, producing a bright fireball over southern Australia.

It had a shield to cope with the heat of re-entry and a parachute for the final drop to the ground.

A recovery team later reported they had identified the landing zone in the Woomera Prohibited Range.

"We just had a spectacular display out over the Outback skies of South Australia," said Professor Trevor Ireland, from the Australian National University, who will get to work on the samples

"We could see the little sample-return capsule separate from the main ship and lead its way in; and [we] just had this magnificent display of the break-up of Hayabusa," he told BBC News.

The Hayabusa mission was launched to asteroid Itokawa in 2003, spending three months at the 500m-long potato-shaped space rock in 2005.

The main spacecraft, along with the sample-storage capsule, should have come back to Earth in 2007, but a succession of technical problems delayed their return by three years.

Even now, there is still some uncertainty as to whether the capsule really does contain pieces of Itokawa.

Although the grab mechanism failed, dust may still have found its way inside

Analysis has shown the Hayabusa spacecraft's capture mechanism malfunctioned at the moment it was supposed to pick up the asteroid rock fragments.

However, Japanese space agency (Jaxa) officials remain confident of success.

They say a lot of dust would have been kicked up when Hayabusa landed on the space rock to make the grab, and some of this material must have found its way inside the probe.

On the journey home, the Hayabusa team had to work around communication drop-outs and propulsion glitches.

But each time an issue came up, the scientists and engineers working on the project managed to find an elegant solution.

Just three hours before the spacecraft began its plunge into Earth's atmosphere, it pushed the sample capsule out in front.

The main spacecraft was destroyed during the descent, accounting for most of the spectacular light show south Australians saw in the night sky.

The container, on the other hand, was equipped with a shield made from carbon phenolic resin which is capable of enduring temperatures that were expected to reach 3,000C on the re-entry.

Radar tracking and a beacon in the canister itself were used by the recovery team to locate the parachute drop-point.

The capsule will not be approached until daylight hours.

"Tomorrow (Monday) or day after tomorrow, we will pick up the capsule itself. Maybe there is some powder or some sample in it," said Yoshiyuki Hasegawa, the associate executive director of Jaxa.

"We will package the capsule and then send it back by aircraft - it's a special aircraft - from the Woomera range to Tokyo International Airport, to go to our facility, our laboratory, where we will analyse the samples."

It could be some months before scientists are able to say with confidence that Hayabusa did indeed capture fragments of Itokawa.

"You hope for grams of sample but you can make do with much less than that," observed Dr Michael Zolensky who worked on Nasa's Stardust comet sample-return mission.

Hayabusa streaks across the sky with the Milky Way in the background

"On Stardust, the entire sample return was on the order of thousands of nano-grams. That was thousands of grains, each of which weighed about one nano-gram; and one of those grains you could spend a year studying," he told BBC News.

Such grains would provide new insight into the early history of the Solar System and the formation of the planets more than 4.5 billion years ago.

Professor Ireland said no rocks on Earth could provide this information because they had been recycled many times.

"If we look at anything on Earth it has been thoroughly through the wringer; it's been messed up by plate-tectonic processes and geochemical processes. So if we want to look at what our Earth was made of, we have to leave Earth. That's the importance of Hayabusa and going to Itokawa."

Jonathan.Amos-INTERNET@bbc.co.uk

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