The latest issue of the journal Science (vol 333 26 August 2011 pp 1113-1131) has six articles on the Hayabusa sample return mission from the asteroid Itokawa. The first article is entitled:
Itokawa Dust Particles: A Direct Link Between S-Type Asteroids and Ordinary Chondrites
The results are from the first samples retrieved from the sample catcher. A Teflon spatula successfully swept about 10% of the sample catcher’s surface. 1534 particles have been identified with the field-emission scanning electron microscope. There were 1087 mono-mineral grains:
The remaining 447 particles bear several minerals, mostly silicates.
The sample catcher was also “tapped” to retrieve additional particles. 38 of these particles have been closely examined. Six are poorly differentiated and 32 are highly differentiated. The 32 highly differentiated particles indicate they have undergone intense thermal metamorphism. There is almost complete partitioning of the Magnesium, Iron and Calcium between pyroxenes. Ordinary chondrite meteorites exhibit thermal metamorphism ranging from unequilibrated type 3 to completely equilibrated type 6. Measurements indicate that the particles formed at a peak temperature of 800 C and cooled slowly to 600 C. The slow cooling indicates that the particles from Itokawa formed at considerable depth. This suggests that the parent body was destroyed by one or more catastrophic impacts. Remnants reformed into present day rubble pile asteroids, including Itokawa.
Petrologic data from the study shows that Itokawa is an ordinary chondrite, linking these asteroids with the corresponding meteorites.