Samples from Itokawa

The Hayabusa spacecraft returned samples of asteroid Itokawa in June of 2010. The first results of the study of these samples was presented in March of 2011. The first wide release of papers by the Japanese researchers appear in the August 26, 2011 issue of Science. Some of their findings are listed here.

The most typical meteorite found on Earth is an ordinary chondrite. It was believed that these came from the most common type of asteroid, the S-type. That makes sense but they aren’t the same color. Instead the asteroids, such as Itokawa, were redder than expected. Study of the returned samples solved the problem. The asteroid has “nanoblobs” on the surface, opaque little bits that are about the size of the wavelength of light and that causes light to scatter. In essence, the asteroids are redder in the same way that a sunset is redder than high noon. The cause of these nanoblobs is not certain but it appears that solar winds are the cause. The analogy isn’t perfect but it seems that S-type asteroids have a sun burn.

Other research solidifies the connection between ordinary chondrite meteorites and S-type asteroids. One way to demonstrate this is to look at the detailed mineral chemistry of the returned samples. This included scanning electron microscope analyses and synchrotron-radiation x-ray diffraction. This research also shows that Itokawa is actually a “reformed” asteroid, an amalgam of pieces from the interior of a (formerly) larger asteroid.

If you are still not convinced of the source of chondrites, another study used the oxygen isotopic composition to create a kind of signature. This signature is found both in the asteroid samples and in samples from chondrites. Both are depleted in the isotope 16O relative to earth materials. Another kind of signature involved the abundance of iridium, depleted on Itokawa and ordinary chondrites compared to carbonaceous chondrites. This suggests that S-type asteroids condensed from the original solar nebula after elements like Iridium had already condensed and thus were somewhat removed from that part of the nebula. This leads one to think that the lifetime of Itokawa is something less than the age of the solar system. This is confirmed by measurements showing Itokawa loses between 10 and 100 centimeters of its surface every one million years.