Asteroid little more than a bulky pile of rubble
Asteroid Itokawa is little more than a loosely gravitationally held heap of debris, apparently left over from an early collision between two smaller asteroids. This was the result of the analysis of the data collected by the Japanese space probe Hayabusa. Hayabusa had made several attempts to briefly land on Itokawa and collect soil samples in November 2005. However, the landing maneuvers failed, and a leak in the fuel supply eventually led to the loss of control of the probe. Before that, however, Hayabusa had been able to send some data about the topology and gravity of the irregularly shaped, 535-meter-long chunk, as well as carried out spectrographic studies.
Itokawa therefore consists of the usual primary building blocks of the planets in the solar system, such as olivine, pyroxene and iron. However, the materials have never melted, which only happens with larger objects with higher gravity. The density of the astonishingly 40 percent porous body is very low. The structure of the asteroid also explains why hardly any impact craters can be seen on it, according to the researchers responsible at the space organization JAXA: A hit would be similar to the impact of a pebble on a sand surface, after which the crater edges are quickly filled in again. Overall, the composition of Itokawa, a so-called "S-type" asteroid, differs greatly from that of other previously studied asteroids, all of which appear to be rather solid rocky bodies.
The currently-failing Hayabusa probe is to be revived with a contingency plan, using a 2007 launch window to Earth with its possibly undamaged ion drive. If no further setbacks occur, the probe could drop its sample container on Earth in 2010. Until then, there is also hope that the uncontrolled landing attempt will fill it with asteroid samples.