Huge Asteroid Impact Formed "Rubble Pile" Space Rock
Discovery among first results from Hayabusa spacecraft's dust sample.
Itokawa is what's known as a rubble-pile asteroid—a body with such low density that the object can't be a solid hunk of rock and instead is most likely made from bits of debris held together by gravity. (See "Shaking Asteroid Sorts, Instead of Sheds, Its Rubble.")
Launched in 2003 by the Japan Aerospace Exploration Agency (JAXA), Hayabusa arrived at Itokawa in 2005. The craft returned to Earth last June, sending its sample-collection capsule to land in the Australian outback while the main body was destroyed in the fiery reentry.
Scientists collected more than 1,500 grains of dust from the sample chamber, and an international team set to work analyzing the particles. (See "First Asteroid Dust Brought to Earth Holds
