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An age–colour relationship for main-belt S-complex asteroids


Asteroid collisions in the main belt eject fragments that may eventually land on Earth as meteorites1,2,3. It has therefore been a long-standing puzzle in planetary science that laboratory spectra of the most populous class of meteorite (ordinary chondrites, OC) do not match the remotely observed surface spectra of their presumed (S-complex) asteroidal parent bodies. One of the proposed solutions to this perplexing observation is that ‘space weathering’ modifies the exposed planetary surfaces over time through a variety of processes (such as solar and cosmic ray bombardment, micro-meteorite bombardment, and so on). Space weathering has been observed on lunar samples4, in Earth-based laboratory experiments5,6, and there is good evidence from spacecraft data that the process is active on asteroid surfaces7,8. Here, we present a measurement of the rate of space weathering on S-complex main-belt asteroids using a relationship between the ages of asteroid families and their colours9. Extrapolating this age–colour relationship to very young ages yields a good match to the colour of freshly cut OC meteorite samples, lending strong support to a genetic relationship between them and the S-complex asteroids.

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Figure 1: The relationship between the mean colour of S-complex asteroid families and their ages.
Figure 2: The distribution of colours for S- and C-complex asteroids detected by the SDSS and the average colours of eight types of ordinary chondrite meteorites.

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We thank C. Chapman and J. Taylor for providing background on the S-complex conundrum and B. Clark for useful discussions and further studies. D.N. thanks NASA PG&G and the SwRI Quicklook programmes for providing support. Funding for the creation and distribution of the SDSS Archive has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the US Department of Energy, the Japanese Monbukagakusho, and the Max Planck Society. The SDSS website is

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Correspondence to Robert Jedicke.

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Supplementary Information

Contains Supplementary Table 1 giving the ages and colours of S-complex asteroids as well as two methods sections summarizing the techniques used for asteroid family identification and age determination. (DOC 60 kb)

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Jedicke, R., Nesvorný, D., Whiteley, R. et al. An age–colour relationship for main-belt S-complex asteroids. Nature 429, 275–277 (2004).

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