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Earth-bound meteorites come from stony asteroids

Hayabusa capsule landed at Woomera in South Australia. This image relates to the paper, "Itokawa Dust Particles: A Direct Link Between S-Type Asteroids and Ordinary Chondrites," by Tomoki Nakamura and colleagues.

Thanks to the Hayabusa space mission, researchers have gotten their first up-close look at dust from the surface of an asteroid. The unmanned Japanese spacecraft was launched in 2003 and sent to the stony, or S-type, asteroid known as 25143 Itokawa. In 2005, it landed on the surface of that asteroid and scooped up some loose dust. Hayabusa returned to Earth in 2010 and researchers from all over the world have been analyzing the asteroid dust ever since.

Studies with the dust have confirmed what researchers suspected all along: that the most common meteorites found here on Earth come from these S-type asteroids. And since the meteorites that land on Earth are among the oldest objects in our solar system, researchers suggest that asteroids have been around just as long, recording a long history of early solar system events.

Tomoki Nakamura and colleagues were among the first researchers to analyze the dust from Itokawa. They looked at the size of the dust grains and the minerals found within them and determined that the Itokawa asteroid must be made up of smaller fragments from a much larger asteroid.

Many other researchers examined the dust grains as well. Keisuke Nagao and colleagues estimate that the loose dust grains have been lying on the surface of the Itokawa asteroid for nearly eight million years. They also compared the samples to dust that was scooped off the surface of the moon long ago and found that Itokawa's dust grains haven not been through as many chemical changes as the dust grains from the moon.

Now, instead of using that moon dust to imagine what asteroid dust is like, researchers can study actual asteroid dust. It should allow researchers to look at the thousands of meteorites that have fallen to Earth and match them up with their "parent" asteroids in space.