Asteroid Itokawa | Japan's Hayabusa Spacecraft
Why are parts of this asteroid's surface so smooth?
The answer seems likely to do with the dynamics of an asteroid that is a loose pile of rubble rather than a solid rock. The unusual asteroid Itokawa was visited by the Japanese spacecraft Hayabusa in 2005 that imaged and documented its unusual structure and mysterious lack of craters. Analyses of the border regions between smooth and rugged sections indicate that jostling of the asteroid might be creating segregation between large and small rocks near the surface, like the "Brazil nut" effect.
25143 Itokawa (provisional designation 1998 SF36) is a sub-kilometer near-Earth object of the Apollo group and also a potentially hazardous asteroid. It was discovered by the LINEAR program in 1998 and later named after Japanese rocket engineer Hideo Itokawa. The peanut-shaped S-type asteroid has a rotation period of 12.1 hours and measures approximately 330 meters (1,100 feet) in diameter. Due to its low density and high porosity, Itokawa is considered to be a rubble pile, consisting of numerous boulders of assorted sizes, rather than a single solid body.
The robotic Hayabusa actually touched down on one of the smooth patches, dubbed the MUSES Sea, and collected soil samples. These samples were returned to Earth and are not only giving clues to the ancient history of this unusual asteroid, but also about the early years of our Solar System. Computer simulations show that 500-meter asteroid Itokawa may impact the Earth within the next few million years.
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