Scientists can't be sure what forces shake up Itokawa. One theory holds that impacts from other objects play a role.
"We show that meteoroids as small as centimeter-scale can shake the entire asteroid sufficiently to create landslides," study leader Miyamoto said.
(Related news: "Asteroids Spin Faster Due to Solar Power, Studies Show" [March 7, 2007].)
And if, as some experts think, Itokawa was once a binary asteroid, shaking could also have been induced when the two objects merged.
Erik Asphaug is a planetary scientist at the University of California, Santa Cruz, who was unaffiliated with the research.
He said the new ideas are convincing but sure to be controversial.
"This is just one more example of an asteroid laughing in our faces," he said.
"We keep thinking we understand asteroids, and then we take a closer look and find them to be stranger than before."
Near-Earth asteroids like Itokawa are of special interest to scientists.
They may contain unchanged remnants from the ancient clusters of cosmic rock that formed Earth and other solid planets some 4.5 billion years ago.
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