Asteroid Itokawa is a Rubble Pile (Porosity of 40%, like sand)

"A small near-Earth asteroid recently visited by a Japanese spacecraft is little more than a "rubble pile" of loosely-pack debris from other asteroid collisions, scientists conclude. In papers published in this week's issue of the journal Science, planetary scientists said studies of the asteroid Itokawa by the Japanese spacecraft Hayabusa showed that the asteroid's surface was littered with small boulders and gravel, leading scientists to conclude that the asteroid is not a monolithic rock but instead debris from a previous asteroid collision held together by its own gravity. The asteroid has a porosity of 40%, further evidence that the object is loosely packed together. Spectroscopic analysis of the asteroid turned up evidence of iron and minerals such as olivine and pyroxene, although no signs of differentiation."

Link: SpaceToday