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 “weathered” over time by solar and cosmic…
