Last week, the small robotic Hayabusa spacecraft arrived at asteroid Itokawa and stationed itself only 20 kilometers away.
Although a long term goal is to find out how much ice, rock and trace elements reside on the asteroid's surface, a shorter term goal is to determine the mass of the asteroid by measuring the attraction of the drifting Hayabusa spacecraft.
During the next few months, Hayabusa will also image and map asteroid Itokawa as it orbits the Sun.
