Rubble Pile in Space

摘要

The Hayabusa spacecraft landed on the Itokawa near-Earth asteroid in 2004 and took crystal-clear pictures of the surface that resolve gravels just centimeters in size. Miyamoto et al. (p. 1011, published online 19 April; see the Perspective by Asphaug) analyzed the surface distribution of the boulders and gravels to document granular processes at work such a low-gravity environment. The regolith appears to have been sorted by shaking, such that the finest material congregates in areas of lowest local gravity. Clumping of larger rocks suggests Itokawa is also stirred up from below by convection of grains.