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Space Weathering on Main Belt Asteroids

Tuesday, May 4, 2004
Robert
Jedicke - Inst. for Astronomy, University of Hawaii

Asteroid collisions in the Main Belt eject fragments that may eventually land on Earth and be identified as meteorites. Given this meteorite progeny it has 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 'space weathering' that modifies the spectrum of exposed planetary surfaces over time through a variety of processes such as solar and cosmic ray bombardment, the cumulative effects of micro-meteorite bombardment and regolith 'gardening' in larger impacts. Space weathering has been observed on lunar samples, in Earth-based laboratory experiments and there is good evidence from spacecraft data that the process is active on asteroid surfaces. Here we present the first measurement for the rate of space weathering on Main Belt asteroids using a relationship between the ages of asteroid families and their colors as measured by the Sloan Digital Sky Survey. Extrapolating this age-color relationship to very young ages yields a good match to the color of freshly cut OC meteorite samples thereby lending strong support to a genetic relationship between them and the S-complex asteroids.

Asteroid collisions in the Main Belt eject fragments that may eventually land on Earth and be identified as meteorites. Given this meteorite progeny it has 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 'space weathering' that modifies the spectrum of exposed planetary surfaces over time through a variety of processes such as solar and cosmic ray bombardment, the cumulative effects of micro-meteorite bombardment and regolith 'gardening' in larger impacts. Space weathering has been observed on lunar samples, in Earth-based laboratory experiments and there is good evidence from spacecraft data that the process is active on asteroid surfaces. Here we present the first measurement for the rate of space weathering on Main Belt asteroids using a relationship between the ages of asteroid families and their colors as measured by the Sloan Digital Sky Survey. Extrapolating this age-color relationship to very young ages yields a good match to the color of freshly cut OC meteorite samples thereby lending strong support to a genetic relationship between them and the S-complex asteroids.

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