Posted: Mon, May 24, 2004, 8:35 AM ET (1235 GMT)
Planetary scientists have published new evidence for a phenomenon called "space weathering" that causes the surfaces of asteroids to change color. A puzzle of asteroid research for decades has been why many asteroids have a reddish color while a class of meteorites, ordinary chondrites, have a bluish color. In a paper published in the current issue of the journal Nature, scientists measured the colors of 100,000 asteroids between six million and three billion years old and found that older asteroids were redder than younger ones, suggesting that some mechanism is changing the color of the asteroids. Scientists hypothesis that exposure to solar and/or cosmic radiation is changing the composition of the surface layers of the asteroids, creating the reddish appearance.

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•  Astronomy article
•  Honolulu Star-Bulletin article
•  SPACE.com article
•  University of Hawaii press release