Spitzer Space Telescope spectra reveal 10 micron silicate emission from circumstellar dust orbiting six externally-polluted white dwarfs. Micron-size glasses with an olivine stoichiometry can account for the distinctively broad wings that extend to 12 microns; these particles likely are produced by tidal-disruption of asteroids. The absence of infrared PAH features is consistent with a scenario where extrasolar rocky planets are assembled from carbon-poor solids.
@article{arxiv.0811.1740,
title = {Six White Dwarfs with Circumstellar Silicates},
author = {M. Jura and J. Farihi and B. Zuckerman},
journal= {arXiv preprint arXiv:0811.1740},
year = {2009}
}