Press Release

Lightsource Illuminates the Puzzle of Asteroid Itokawa

Aug 26, 2011

Tohoku University
High Energy Accelerator Research Organization (KEK)

Researchers led by Associate Professor Tomoki Nakamura at the Department of Earth and Planetary Materials Science, Tohoku University, have uncovered the dramatic early history of the small asteroid Itokawa by analyzing tiny granular samples returned to Earth by JAXA's Asteroid Explorer Hayabusa.

"We concluded that the parent body of Itokawa was initially about 20 km in diameter," says Nakamura. "The temperature at the core of the parent asteroid reached 800 deg. C, then slowly cooled down. But then another asteroid struck and smashed the original Itokawa. What we see as Itokawa now is a remnant, just a small fraction of the original, consisting of the fragments that were brought back together and recombined by their small gravity."

The team analyzed 38 tiny grains of Itokawa samples brought back to Earth by Hayabusa, using X-ray diffraction and high-resolution electron microscopy. "The KEK Photon Factory has an ideal lightsource beam line to analyze the composition of minerals in small samples, ranging from 30 to 150 micrometers," explains Nakamura. "We also used a high-resolution electron microscope to examine the structure and chemical composition of various minerals inside the samples. We found that some samples had experienced significant thermal metamorphism, indicating that they came from the high-temperature environment of the interior of the parent asteroid. We also used the other lightsource facility SPring-8 to further examine some samples containing plagioclase."

Major minerals identified in Itokawa samples are: olivine, low-Ca pyroxene, high-Ca pyroxene, and plagioclase. Less abundant but common minerals are: troilite, taenite, and chromite. This suggests that Itokawa is similar in mineral composition to chondrite meteorites, the oldest and most primitive material in the solar system.

These results, combined with other analyses of Itokawa samples, appear in the special Hayabusa issue of Science (August 25, 2011).