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Research finds asteroid Itokawa is an ancient rock

Posted: March 13, 2011

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A preliminary analysis of asteroid samples returned last year by Japan's Hayabusa probe show evidence the dust grains have a similar composition to stony meteorites that commonly fall to Earth.

This image of one of Hayabusa's samples was obtained with a scanning electron microscope. Credit: JASA
Hayabusa returned to Earth last June with a fiery plunge into the Australia outback. The seven-year robotic mission surveyed asteroid Itokawa, a potato-shaped rock about the size of a city block.

The initial research also shows the samples inspected so far contain no organic molecules. Scientists also say the analysis confirms the rocks at Itokawa were formed 4.6 billion years ago at the dawn of the solar system.

Researchers believe Itokawa itself was formed when several existing smaller bodies accreted into a larger asteroid. Scientists describe such asteroids as "rubble pile" objects.

The early results were presented last week at the Lunar and Planetary Science conference in Houston.

Hayabusa was intended to approach the surface of Itokawa, fire a pellet into the regolith and collect bits of rock in a funnel leading to the spacecraft's sample chamber.

But in two sampling attempts in late 2005, the projectile didn't fire and scientists feared the mission was a failure.

A crippling fuel leak, ion engine failures, reaction wheel glitches, battery issues and a two-month communications loss challenged mission controllers during Hayabusa's flight. Officials had to delay the mission's return to Earth from 2007 until 2010 to deal with the issues.

Photo of asteroid Itokawa during Hayabusa's visit in 2005. Credit: JASA
An analysis of telemetry later showed Hayabusa landed on Itokawa for up to a half-hour during one of the sampling attempts, giving scientists renewed hope the probe may have gathered some small dust grains in its time on the asteroid.

Researchers confirmed their hopes last year when they opened Hayabusa's sample return capsule in a clean room in Sagamihara, Japan.

They found at least 1,500 individual grains, most of which were confirmed to be from asteroid Itokawa.

Most of the particles were less than 10 microns in diameter, but a few samples were 100 microns or larger, comparable to the width of a strand of human hair, according to papers presented by Japanese scientists.

Teams started their preliminary analyses of the samples in January and expect to finish their first round of examinations by June at the curation facility in Sagamihara. The material will then be distributed to other research sites for further study.

NASA will get about 10 percent of the material in return for U.S. contributions to the mission's operations and sample recovery efforts.

Hayabusa was the first mission to retrieve samples from the surface of an asteroid and bring them back to Earth.