Japanese scientists say they're certain that particles captured by the Hayabusa spacecraft are indeed from the Itokawa asteroid.
Japan's space agency, Jaxa, says that scanning electron microscope analysis of the 1,500 particles collected by the probe proves they can't be of terrestrial origin.
The particles are tiny, mostly lesss than ten micrometers across, and include the minerals olivine, pyroxene and plagioclase.
"The mineral phases among the collected 1,500 particles, their relative abundance ratios and their elemental compositions agree with a class of primitive meteorite, and they do not correspond to any rock type on the surface of the Earth," says Jaxa. "The minerals are consistent with the surface material predicted by the remote sensing instruments carried on board Hayabusa."
It's the first time material has ever been collected from an asteroid - or, indeed, from any non-terrestrial body other than the moon.
In a seven-year mission - three years longer than planned, thanks to a series of defective parts - the probe collected samples in 2005. It returned to Earth in June, but at the time Jaxa warned that there might be nothing inside - or that any material might simply represent contamination from Earth.
Jaxa hopes that the sample will provide information on how and when Itokawa was formed, what exactly it's composed of, and whether it's been in contact with any other bodies.