astroengine writes "We care about how asteroids are made, in large part because if one were aiming to smash into us, we'd like to know what we can do about it. The structure of asteroids is also a matter of scientific curiosity, as it tells us a bit about the formation and evolution in our solar system. ... 25143 Itokawa is a relatively small near-Earth asteroid that was visited by the Japanese Habayusa spacecraft in 2005. It has also been monitored by Stephen Lowry of the University of Kent and his colleagues over a twelve year span with the 3.58 meter New Technology Telescope in La Silla, Chile. In that time span, Itokawa has made five near approaches to Earth. And what did they find? The asteroid is composed of two lobes of different densities, suggesting that Itokawa is in fact a merged binary." ESO is hosting a preprint of the paper.