PerspectivePlanetary Science

Bringing Part of an Asteroid Back Home

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Science  26 Aug 2011:
Vol. 333, Issue 6046, pp. 1098-1099
DOI: 10.1126/science.1212145

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Meteorites are the oldest rocks in our solar system, and therefore record the earliest stages of its evolution. On the basis of their mineralogy, petrography, bulk chemistry, and oxygen-isotope compositions, meteorites are classified into more than 70 groups. Each group is believed to represent samples of one or a few larger bodies that formed early in the solar system and may still be represented by asteroids (1) in the main asteroid belt, which lies between the orbits of Mars and Jupiter. Various types of asteroids have been identified based on their spectral properties. Linking the meteorite groups to these asteroid types is critical for assessing the meteorite data and using it as a basis for inferring, for example, the composition and growth of Earth and other planets. Because we have lacked direct samples of specific asteroids, we have had to rely on remote observations of asteroids and relate them to the meteorite groups. This has been problematic because the surfaces of asteroids have been heavily modified by space weathering, which changes their spectral properties. To establish such a connection and understand the role of space weathering, the JAXA (Japan Aerospace Exploration Agency) spacecraft Hayabusa was sent to near-Earth asteroid 25143 Itokawa, which is 0.5 by 0.3 by 0.2 km in size to collect and bring back to Earth samples of its surface (see the figure). Itokawa is an S-type asteroid, the most abundant spectral type of asteroid in the inner asteroid belt.

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