THE surface of an asteroid changes colour as it ages. The finding has solved a long-standing puzzle about why meteorites, which are thought to be fresh fragments of asteroids, are not the same colour as their parents.
A team of astronomers led by Robert Jedicke of the University of Hawaii in Honolulu has measured the colour of over 8000 so-called S-type asteroids, whose approximate ages are well known (Nature, vol 429, p 275). After allowing for differences in mineral composition, the team found a clear link between age and colour, as asteroids are 鈥渨eathered鈥� over time by solar and cosmic rays.
The researchers then extrapolated the data to calculate the colour of very young rocks. Their prediction matched the colour of freshly cut lab samples of the most common meteorites, strongly supporting the idea that these were chipped off by collisions between S-type asteroids.
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