Japan's Hayabusa probe returns to Earth today, releasing a capsule into the atmosphere that scientists hope will contain samples from asteroid Itokawa. No-one really knows whether Hayabusa succeeded in grabbing samples from Itokawa's surface during a 2005 visit. Hayabusa was launched in 2003 and used ion engines to propel itself out to Itokawa, a 500 meter-long potato-shaped rock which drifts between the orbit of Earth and beyond Mars.